Hereditary sensory and autonomic neuropathy type III (HSAN III, Riley–Day syndrome, Familial Dysautomia) is characterised by elevated thermal thresholds and an indifference to pain. Using microelectrode recordings we recently showed that these patients possess no functional stretch-sensitive mechanoreceptors in their muscles (muscle spindles), a feature that may explain their lack of stretch reflexes and ataxic gait, yet patients have apparently normal low-threshold cutaneous mechanoreceptors. The density of C-fibres in the skin is markedly reduced in patients with HSAN III, but it is not known whether the C-tactile afferents, a distinct type of low-threshold C fibre present in hairy skin that is sensitive to gentle stroking and has been implicated in the coding of pleasant touch are specifically affected in HSAN III patients. We addressed the relationship between C-tactile afferent function and pleasant touch perception in 15 patients with HSAN III and 15 age-matched control subjects. A soft make-up brush was used to apply stroking stimuli to the forearm and lateral aspect of the leg at five velocities: 0.3, 1, 3, 10 and 30 cm/s. As demonstrated previously, the control subjects rated the slowest and highest velocities as less pleasant than those applied at 1–10 cm/s, which fits with the optimal velocities for exciting C-tactile afferents. Conversely, for the patients, ratings of pleasantness did not fit the profile for C-tactile afferents. Patients either rated the higher velocities as more pleasant than the slow velocities, with the slowest velocities being rated unpleasant, or rated all velocities equally pleasant. We interpret this to reflect absent or reduced C-tactile afferent density in the skin of patients with HSAN III, who are likely using tactile cues (i.e. myelinated afferents) to rate pleasantness of stroking or are attributing pleasantness to this type of stimulus irrespective of velocity.
•C-tactile afferents in hairy skin are believed to mediate affective touch.•They are sensitive to slow brushing stimuli, which are perceived as pleasant.•It is not known whether C-tactile afferents are affected in HSAN III.•Ratings of pleasantness were reduced in 15 HSAN III patients compared to controls.•We suggest that the density of C-tactile afferents is reduced in HSAN III.
Affective touch; CT afferents; Pleasant touch; Tactile sensation
Hereditary sensory and autonomic neuropathy type III features a marked ataxic gait that progressively worsens over time. We assessed whether proprioceptive disturbances can explain the ataxia. Proprioception at the knee joint was assessed using passive joint angle matching in 18 patients and 14 age-matched controls; 5 patients with cerebellar ataxia were also studied. Ataxia was quantified using the Brief Ataxia Rating Score, which ranged from 7 to 26/30. Neuropathy patients performed poorly in judging joint position: mean absolute error was 8.7±1.0° and the range was very wide (2.8–18.1°); conversely, absolute error was only 2.7±0.3° (1.6–5.5°) in the controls and 3.0±0.2° (2.1–3.4°) in the cerebellar patients. This error was positively correlated to the degree of ataxia in the neuropathy patients but not the cerebellar patients, suggesting that poor proprioceptive acuity at the knee joint is a major contributor to the ataxic gait associated with hereditary sensory and autonomic neuropathy type III.
congenital insensitivity to pain; familial dysautonomia; joint sense; hereditary sensory & autonomic neuropathy; muscle spindles; proprioception; Riley-Day syndrome
Peripheral neuropathies are a heterogeneous group of diseases affecting peripheral nerves. The causes are multiple: hereditary, metabolic, infectious, inflammatory, toxic, traumatic. The temporal profile includes acute, subacute and chronic conditions. The majority of peripheral neuropathies cause mainly muscle weakness and sensory loss, positive sensory symptoms and sometimes pain. When pain is present, however, it is usually extremely intense and among the most disabling symptoms for the patients. In addition, the neurological origin of the pain is often missed and patients receive inadequate or delayed specific treatment. Independently of the disease causing the peripheral nerve injury, pain originating from axonal pathology or ganglionopathy privileges neuropathies affecting smaller fibres, a clinical observation that points towards abnormal activity within nociceptive afferents as a main generator of pain. Natural activation of blood vessels or perineurial nociceptive network by pathology also causes intense pain. Pain of this kind, i.e. nerve trunk pain, is among the heralding symptoms of inflammatory or ischemic mononeuropathy and for its intensity represents itself a medical emergency. Neuropathic pain quality rekindles the psychophysical experience of peripheral nerves intraneural microstimulation i.e. a combination of large and small fibres sensation temporally distorted compared to physiological perception evoked by natural stimuli. Pins and needles, burning, cramping mixed with numbness, and tingling are the wording most used by patients. Nociceptive pain instead is most often described as aching, deep and dull. Good command of peripheral nerve anatomy and pathophysiology allows timely recognition of the different pain components and targeted treatment, selected according to intensity, type and temporal profile of the pain.
Pain; neuropathic; polyneuropathy; small fibres neuropathy; diabetic neuropathy; post herpetic neuralgia; paraneoplastic polyneuropathy; hereditary neuropathy
Twenty-eight mechanoreceptive units identified as primary or secondary spindle afferents were sampled from muscle nerve fascicles in the median, peroneal, and tibial nerves of healthy adult subjects. The responses of these units to sustained passive muscle stretch, to passive stretching movements, to tendon taps, and electrically-induced muscle twitches were studied while the subject performed repeated Jendrassik manoeuvres involving strong voluntary contractions in distant muscle groups. The manoeuvres had no effect upon the afferent spindle discharges as long as there were no EMG signs of unintentional contractions occurring in the receptor-bearing muscle and no mechanotransducer signs of unintentional positional changes altering the load on that muscle. Unintentional contractions in the receptor-bearing muscle frequently occurred during the manoeuvres, however, and then coactivation of the spindle afferents was observed. Multiunit afferent responses to Achilles tendon taps, led off from tibial nerve fascicles, were in a similar way uninfluenced by the Jendrassik manoeuvres, even when these resulted in marked reinforcement of the calf muscle tendon jerk. The results provide no evidence for fusimotor sensitization of spindles in muscles remaining relaxed during the Jendrassik manoeuvre, and reflex reinforcement occurring without concomitant signs of active tension rise in the muscles tested is presumed to depend upon altered processing of the afferent volleys within the cord.
Five members of a single family presented with neuropathic deformities and ulceration of the feet developing in the first and second decades of life, and progressed slowly over many years. In this form of hereditary sensory and autonomic neuropathy, there was minimal tendon reflex impairment, cutaneous sensory impairment was restricted to the feet, and there was no autonomic dysfunction. The only neurophysiological abnormality was that of reduced or absent sural nerve sensory action potentials. Sural nerve biopsies taken from two affected family members showed changes of a chronic neuropathy with loss of myelinated fibres, particularly affecting those of small diameter. Unmyelinated fibres were present in normal numbers. This condition differed from other forms of hereditary sensory and autonomic neuropathy having an X-linked recessive mode of inheritance.
Congenital insensitivity to pain with anhidrosis, also known as hereditary sensory and autonomic neuropathy type IV, is an autosomal recessive disorder characterized by the congenital lack of pain sensation, inability to sweat, episodes of recurrent hyperpyrexia, mental retardation, and self-mutilating behavior. It is an extremely rare disorder with only a handful of reports from India. A five- year- old boy, born to second-degree consanguineous parents after uneventful antenatal period, presented to us with history of recurrent unexplained fever, recurrent ulcers in the lower limbs, insensitivity to painful stimuli (like injections, vaccination) and self-mutilating behavior from early childhood. Cutaneous examination showed multiple ulcers, loss of teeth, loss of tip of the tongue (due to biting), scarring of finger tips, xerosis and lichenification. Sensory examination showed complete loss of pain and temperature sensations, but fine touch and vibration were preserved. Deep tendon reflexes were normal. Evaluation for Hansen's disease was non-contributory. An intradermal injection of histamine did not show any flare response. Based on clinical as well as compatible histological features a diagnosis of congenital insensitivity to pain with anhidrosis was made. The ulcers were treated with appropriate antibiotics and daily dressings. The parents were counseled about appropriate care of the child.
Congenital insensitivity to pain with anhidrosis; hereditary sensory and autonomic neuropathy type IV; self-mutilation
The hereditary sensory and autonomic neuropathies (HSAN) encompass a number of inherited disorders that are associated with sensory dysfunction (depressed reflexes, altered pain and temperature perception) and varying degrees of autonomic dysfunction (gastroesophageal reflux, postural hypotention, excessive sweating). Subsequent to the numerical classification of four distinct forms of HSAN that was proposed by Dyck and Ohta, additional entities continue to be described, so that identification and classification are ongoing. As a group, the HSAN are rare diseases that affect both sexes. HSAN III is almost exclusive to individuals of Eastern European Jewish extraction, with incidence of 1 per 3600 live births. Several hundred cases with HSAN IV have been reported. The worldwide prevalence of HSAN type II is very low. This review focuses on the description of three of the disorders, HSAN II through IV, that are characterized by autosomal recessive inheritance and onset at birth. These three forms of HSAN have been the most intensively studied, especially familial dysautonomia (Riley-Day syndrome or HSAN III), which is often used as a prototype for comparison to the other HSAN. Each HSAN disorder is likely caused by different genetic errors that affect specific aspects of small fiber neurodevelopment, which result in variable phenotypic expression. As genetic tests are routinely used for diagnostic confirmation of HSAN III only, other means of differentiating between the disorders is necessary. Diagnosis is based on the clinical features, the degree of both sensory and autonomic dysfunction, and biochemical evaluations, with pathologic examinations serving to further confirm differences. Treatments for all these disorders are supportive.
Hereditary sensory neuropathy type I (HSN I) is a slowly progressive neurological disorder characterised by prominent predominantly distal sensory loss, autonomic disturbances, autosomal dominant inheritance, and juvenile or adulthood disease onset. The exact prevalence is unknown, but is estimated as very low. Disease onset varies between the 2nd and 5th decade of life. The main clinical feature of HSN I is the reduction of sensation sense mainly distributed to the distal parts of the upper and lower limbs. Variable distal muscle weakness and wasting, and chronic skin ulcers are characteristic. Autonomic features (usually sweating disturbances) are invariably observed. Serious and common complications are spontaneous fractures, osteomyelitis and necrosis, as well as neuropathic arthropathy which may even necessitate amputations. Some patients suffer from severe pain attacks. Hypacusis or deafness, or cough and gastrooesophageal reflux have been observed in rare cases. HSN I is a genetically heterogenous condition with three loci and mutations in two genes (SPTLC1 and RAB7) identified so far. Diagnosis is based on the clinical observation and is supported by a family history. Nerve conduction studies confirm a sensory and motor neuropathy predominantly affecting the lower limbs. Radiological studies, including magnetic resonance imaging, are useful when bone infections or necrosis are suspected. Definitive diagnosis is based on the detection of mutations by direct sequencing of the SPTLC1 and RAB7 genes. Correct clinical assessment and genetic confirmation of the diagnosis are important for appropriate genetic counselling and prognosis. Differential diagnosis includes the other hereditary sensory and autonomic neuropathies (HSAN), especially HSAN II, as well as diabetic foot syndrome, alcoholic neuropathy, neuropathies caused by other neurotoxins/drugs, immune mediated neuropathy, amyloidosis, spinal cord diseases, tabes dorsalis, lepra neuropathy, or decaying skin tumours like amelanotic melanoma. Management of HSN I follows the guidelines given for diabetic foot care (removal of pressure to the ulcer and eradication of infection, followed by the use of specific protective footwear) and starts with early and accurate counselling of patients about risk factors for developing foot ulcerations. The disorder is slowly progressive and does not influence life expectancy but is often severely disabling after a long duration of the disease.
OBJECTIVE—To develop a
method for the detection of bilateral Horner's syndrome in patients
with bilateral interruption of the cervical sympathetic pathway or
widespread autonomic neuropathy.
pupil diameters and redilatation times during light reflexes have been
recorded with infrared TV pupillometry in 65 healthy subjects, 47 patients with unilateral Horner's syndrome, and 20 patients with
bilateral Horner's syndrome. The aetiologies of the last group were
diabetic autonomic neuropathy (three cases), amyloidosis (four), pure
autonomic failure (PAF) (four), dopamine-β-hydroxylase deficiency
(two), and one case each of hereditary sensory and autonomic neuropathy
(HSAN) type III, carcinomatous sympathetic neuropathy, familial
dysautonomia, multiple system atrophy, Anderson-Fabry disease, and
anterior spinal artery thrombosis at C5,6 and one had had bilateral
diameters on the affected side were below normal in 12 patients with
unilateral Horner's syndrome, the measurement yielding only 26%
sensitivity for detection of the condition. By contrast, the time taken
to reach three quarter recovery in the light reflex (T3/4)
was abnormally prolonged (redilatation lag) in 33 of the same eyes. The
measurement yielded 70% sensitivity and 95% specificity for detection
of the condition. In 20 cases, diagnosed on clinical grounds as having
bilateral Horner's syndrome of various aetiologies, pupil diameters
were abnormally small on both sides in five and on one side in three
patients. Fourteen of these patients had significant redilatation lag
in both eyes, five patients in one eye, and one patient had it in
neither eye. Measurement of redilatation lag was therefore a more
sensitive diagnostic test than pupil diameter in both unilateral and
bilateral Horner's syndrome.
that the pupils are not tonic, bilateral Horner's syndrome can be
diagnosed on the basis of redilatation lag. It occurs clinically in
some generalised autonomic neuropathies and with interruption of the
local sympathetic nerve supplies to the two eyes.
Peripheral neuropathy refers to disorders of the peripheral nervous system. They have numerous causes and diverse presentations; hence, a systematic and logical approach is needed for cost-effective diagnosis, especially of treatable neuropathies. A detailed history of symptoms, family and occupational history should be obtained. General and systemic examinations provide valuable clues. Neurological examinations investigating sensory, motor and autonomic signs help to define the topography and nature of neuropathy. Large fiber neuropathy manifests with the loss of joint position and vibration sense and sensory ataxia, whereas small fiber neuropathy manifests with the impairment of pain, temperature and autonomic functions. Electrodiagnostic (EDx) tests include sensory, motor nerve conduction, F response, H reflex and needle electromyography (EMG). EDx helps in documenting the extent of sensory motor deficits, categorizing demyelinating (prolonged terminal latency, slowing of nerve conduction velocity, dispersion and conduction block) and axonal (marginal slowing of nerve conduction and small compound muscle or sensory action potential and dennervation on EMG). Uniform demyelinating features are suggestive of hereditary demyelination, whereas difference between nerves and segments of the same nerve favor acquired demyelination. Finally, neuropathy is classified into mononeuropathy commonly due to entrapment or trauma; mononeuropathy multiplex commonly due to leprosy and vasculitis; and polyneuropathy due to systemic, metabolic or toxic etiology. Laboratory investigations are carried out as indicated and specialized tests such as biochemical, immunological, genetic studies, cerebrospinal fluid (CSF) examination and nerve biopsy are carried out in selected patients. Approximately 20% patients with neuropathy remain undiagnosed but the prognosis is not bad in them.
Axonal demyelination; diagnosis; nerve conduction; peripheral neuropathy
Spinal integration of sensory signals associated with hip position, muscle loading, and cutaneous sensation of the foot contributes to movement regulation. The exact interactive effects of these sensory signals under controlled dynamic conditions are unknown. The purpose of the present study was to establish the effects of combined plantar cutaneous afferent excitation and hip movement on the Hoffmann (H) and flexion reflexes in people with a spinal cord injury (SCI). The flexion and H-reflexes were elicited through stimulation of the right sural (at non-nociceptive levels) and posterior tibial nerves respectively. Reflex responses were recorded from the ipsilateral tibialis anterior (TA) (flexion reflex) and soleus (H-reflex) muscles. The plantar cutaneous afferents were stimulated at three times the perceptual threshold (200 Hz, 24-ms pulse train) at conditioning–test intervals that ranged from 3 to 90 ms. Sinusoidal movements were imposed to the right hip joint at 0.2 Hz with subjects supine. Control and conditioned reflexes were recorded as the hip moved in flexion and extension. Leg muscle activity and sagittal-plane joint torques were recorded. We found that excitation of plantar cutaneous afferents facilitated the soleus H-reflex and the long latency flexion reflex during hip extension. In contrast, the short latency flexion reflex was depressed by plantar cutaneous stimulation during hip flexion. Oscillatory joint forces were present during the transition phase of the hip movement from flexion to extension when stimuli were delivered during hip flexion. Hip-mediated input interacts with feedback from the foot sole to facilitate extensor and flexor reflex activity during the extension phase of movement. The interactive effects of these sensory signals may be a feature of impaired gait, but when they are appropriately excited, they may contribute to locomotion recovery in these patients.
H-reflex; Flexion reflex; Locomotion; Reflex circuits; Rehabilitation; Sensorimotor integration
Spinal manipulation (SM) is a form of manual therapy used clinically to treat patients with low back and neck pain. The most common form of this maneuver is characterized as a high velocity (duration < 150ms), low amplitude (segmental translation < 2mm, rotation < 4°, and applied force 220-889N) impulse thrust (HVLA-SM). Clinical skill in applying an HVLA-SM lies in the practitioner's ability to control the duration and magnitude of the load (i.e., the rate of loading), the direction in which the load is applied, and the contact point at which the load is applied. Control over its mechanical delivery presumably related to its clinical effects. Biomechanical changes evoked by an HVLA-SM are thought to have physiological consequences caused, at least in part, by changes in sensory signaling from paraspinal tissues.
If activation of afferent pathways does contribute to the effects of an HVLA-SM, it seems reasonable to anticipate that neural discharge might increase or decrease in a non-linear fashion as the thrust duration thrust approaches a threshold value. We hypothesized that the relationship between the duration of an impulsive thrust to a vertebra and paraspinal muscle spindle discharge would be non-linear with an inflection near the duration of an HVLA-SM delivered clinically (<150ms). In addition, we anticipated that muscle spindle discharge would be more sensitive to larger amplitude thrusts.
A neurophysiological study of spinal manipulation using the lumbar spine of a feline model.
Impulse thrusts (duration: 12.5, 25, 50, 100, 200, and 400 ms; amplitude 1 or 2mm posterior to anterior) were applied to the spinous process of the L6 vertebra of deeply anesthetized cats while recording single unit activity from dorsal root filaments of muscle spindle afferents innervating the lumbar paraspinal muscles. A feedback motor was used in displacement control mode to deliver the impulse thrusts. The motor's drive arm was securely attached to the L6 spinous process via a forceps.
As thrust duration became shorter the discharge of the lumbar paraspinal muscle spindles increased in a curvilinear fashion. A concave up inflection occurred near the 100ms duration eliciting both a higher frequency discharge compared to the longer durations and a substantially faster rate of change as thrust duration was shortened. This pattern was evident in paraspinal afferents with receptive fields both close and far from the midline. Paradoxically, spindle afferents were almost twice as sensitive to the 1mm compared to the 2mm amplitude thrust (6.2 vs 3.3 spikes/s/mm/s). This latter finding may be related to the small vs large signal range properties of muscle spindles.
. The results indicate that the duration and amplitude of a spinal manipulation elicits a pattern of discharge from paraspinal muscle spindles different from slower mechanical inputs. Clinically, these parameters may be important determinants of an HVLA-SM's therapeutic benefit.
lumbar spine; spinal manipulation; chiropractic; osteopathy; paraspinal muscles; muscle spindle
Classic chronic inflammatory demyelinating polyneuropathy (CIDP), an acquired demyelination of peripheral nerves and nerve roots presents with symmetric motor and sensory involvement, weakness in proximal and distal muscles, globally diminished or absent reflexes, painful dysesthesias, and back pain with no brain involvement. In this case, a highly functional lawyer presents with reversible dementia and motor and sensory symptoms consistent with CIDP. This case may represent a new clinical entity of CIDP with reversible dementia.
A 60-year-old man presented with progressive weakness, and cognitive dysfunction in the form of dementia over the last 8 weeks. Sensory and motor weakness continued to progress affecting upper and lower extremities with both proximal and distal muscle groups to the point where the patient was unable to move without assistance. The patient had word finding difficulty, short-term memory impairment, and was disoriented, despite his comprehension being intact. Initial Montreal Cognitive Assessment (MoCA) was 12/30. Initial neurologic exam was notable for muscle strength 3/5, globally depressed deep tendon reflexes. Lumbar puncture revealed elevated protein with no pleocytosis and no serum paraprotein. EMG/NCS demonstrated mixed sensorimotor axonal and demyelination peripheral polyneuropathy. CIDP was diagnosed based on clinical history according to Koski criteria. He was started on a 5-day treatment of IVIG, after which he had marked cognitive improvement after just one dose and improvement in weakness after the second dose of IVIG. Three weeks after IVIG treatment, the patient's cognitive function was back at baseline with MoCA score 29/30; no further word finding difficulty, and no short term memory impairment. At discharge, the patient's weakness had significantly improved to the point where he was able to walk with only the aid of a walker. His neurologic exam had improved as well as his muscle strength 4/5 and 2/4 deep tendon reflexes. Left sural nerve biopsy would eventually reveal moderate peripheral neuropathy with axonal degeneration, moderate loss of large and small myelinated nerve fibers, confirming diagnosis of CIDP.
CIDP encompasses several different variants, including Lewis-Sumner syndrome, distal acquired demyelinating sensory neuropathy, sensory predominant CIDP among other variants. However, none of the variations of CIDP have a reversible cognitive impairment component. Patient met diagnosis of CIDP according to Koski criteria, as he had chronic polyneuropathy progressive for at least 8 weeks with no serum paraprotein, no genetic abnormality, and symmetric exam revealing weakness in all four limbs and proximal weakness in both lower extremities. Potentially, the patient could have had simultaneous diagnosis of dementia and CIDP, but the marked improvement in cognitive function after just one dose of IVIG makes that theory unlikely. PubMed search yielded no single case of CIDP with supratentorial manifestations in a patient with normal brain MRI. This case may represent a new clinical variant: CIDP with cognitive impairment.
To determine whether central nervous conduction deficits are related to the degree of peripheral neuropathy somatosensory evoked potentials (SEP) were measured after tibial nerve stimulation in 51 healthy subjects aged 39.3 (SE 2.0, (range 21-71) years and 100 insulin dependent diabetic patients aged 37.3 (1.5, 18-73) years. Five criteria were used for staging of peripheral neuropathy: nerve conduction; thermal discrimination threshold; vibration perception threshold; tendon reflexes; and neuropathic symptoms. Thirty seven patients had fewer than two abnormalities among the first four criteria and no symptoms (stage 0 = no neuropathy), 37 had 2 or more abnormalities but no symptoms (stage 1 = subclinical neuropathy); 26 had 2 or more abnormalities in conjunction with symptoms (stage 2 = symptomatic neuropathy). Multiple regression analysis was used to define the age and height dependent limits of normal of SEP at the 97.5th and 2.5th centiles. In five patients with stage 1, seven patients with stage 2, but no patient with stage 0 the individual SEP components were unrecordable. The relative frequencies of abnormally prolonged or non-evokable popliteal N8 latency as well as cortical N33 latency and N33/P40 amplitude increased significantly from stage 0 (3-30%) to stage 1 (22-62%) and stage 2 (46-84%) (p < 0.05 for each component and stage). The numbers and percentages of abnormal recordable spinal N22-30 and supraspinal N30-33 interpeak latencies were two (6.3%) and four (11.8%) in patients with stage 0, but these rates did not increase in subjects with stage 1 or 2. The components of SEP were significantly associated with the indices of peripheral and autonomic function tests. There were no major relations between the latencies of SEP and duration of diabetes or prevailing glycaemic control. These findings suggest that the degree of dysfunction along the somatosensory afferent pathways in insulin dependent diabetic patients depends on the stage of peripheral neuropathy; is not related to the degree of glycaemic control or duration of diabetes; and can be characterized mainly by an alteration of the cortical sensory complex and peripheral transmission delay, while spinal and supraspinal conduction deficits are detected infrequently.
The experiments reported in this paper tested the hypothesis that the afferent potential elicited by a tendon tap in an isometrically recorded phasic stretch reflex can be detected in the surface EMG of normal humans when appropriate techniques are used. These techniques involved (1) training the subjects to relax mentally and physically so that the EMG was silent before and immediately after the diphasic MAP which reflects a highly synchronous discharge of afferent impulses from low threshold muscle stretch receptors after a tendon tap, and (2) using a data retrieval computer to summate stimulus-locked potentials in the EMG over a series of 16 samples using taps of uniform peak force and duration on the Achilles tendon to elicit the tendon jerk in the calf muscles. A discrete, diphasic potential (`A-wave') was recorded from EMG electrodes placed on the surface of the skin over the medial gastrocnemius muscle. The `A-wave' afferent potential had the opposite polarity to the corresponding efferent MAP. Under control conditions of relaxation the `A-wave' had a latency after the onset of the tap of 2 msec, the peak to peak amplitude was of the order of 5 μV and the duration was in the range of 6 to 10 msec. Further experiments were conducted to show that the `A-wave' (1) was not an artefact of the instrumentation used, (2) had a threshold at low intensities of stimulation, and (3) could be reliably augmented by using a Jendrassik manoeuvre compared with the potential observed during control (relaxation) conditions. The results support the conclusion that the `A-wave' emanates from the pool of muscle spindles which discharges impulses along group Ia nerve fibres in response to the phasic stretch stimulus because the primary ending of the spindles is known to initiate the stretch reflex and the spindles can be sensitized by fusimotor impulses so that their threshold is lowered as a result of a Jendrassik manoeuvre. The finding has important implications for the investigation of the fusimotor system in intact man.
Muscle spindles provide proprioceptive feedback supporting normal patterns of motor activity and kinesthetic sensibility. During mastication, jaw muscle spindles play an important role in monitoring and regulating the chewing cycle and the bite forces generated during mastication. Both acute and chronic orofacial pain disorders are associated with changes in proprioceptive feedback and motor function. Experimental jaw muscle pain also alters the normal response of masseter spindle afferents to ramp and hold jaw movements . It has been proposed that altered motor function and proprioceptive input results from group III muscle afferent modulation of the fusimotor system which alters spindle afferent sensitivity in limb muscles. The response to nociceptive stimuli may enhance or reduce the response of spindle afferents to proprioceptive stimuli. Several experimental observations suggesting the possibility that a similar mechanism also functions in jaw muscles are presented in this report. First, evidence is provided to show that nociceptive stimulation of the masseter muscle primarily influences the amplitude sensitivity of spindle afferents with relatively little effect on the dynamic sensitivity . Second, reversible inactivation of the caudal trigeminal nuclei attenuates the nociceptive modulation of spindle afferents. Finally, functionally identified gamma-motoneurons in the trigeminal motor nucleus are modulated by intramuscular injection with algesic substances. Taken together, these results suggest that pain-induced modulation of spindle afferent responses are mediated by small diameter muscle afferents and that this modulation is dependent, in part, on the relay of muscle nociceptive information from trigeminal subnucleus caudalis onto trigeminal gamma-motoneurons. The implication of these results will be considered in light of current theories on the relationship between jaw muscle pain and oral motor function.
Muscle spindle afferents; Masseter muscle; Pain; Proprioception; Rats
Congenital insensitivity to pain and anhidrosis (CIPA) or hereditary sensory autonomic neuropathies type IV (HSAN type IV) is an extremely rare autosomal recessive disorder initially described by Swanson in 1963.
We report a 2.5-year-old boy with clinical features of CIPA as the first case in Iran. The symptoms included recurrent episodes of hyperthermia and unexplained fever that began in early infancy, anhidrosis (inability to sweat), profound loss of pain sensitivity, neurodevelopmental delay, unconscious self-mutilation of fingers, lips and tongue, corneal lacerations, palmar hyperkeratosis, non-painful fracture and joint deformities in the right ankle. Tearing, deep tendon reflexes and motor and sensory nerve action potentials were normal.
Prenatal screening is the sole accessible option to prevent the birth of an affected child as no cure is available. Early recognition of CIPA patients and its orthopedic complications, prevention of accidental injuries, regular visual and eye follow-up and specific dental management could be useful in the reduction of frequency and severity of complications.
HSAN type IV; Congenital insensitivity to pain; Anhidrosis
Single unit activity in spindle afferent nerve fibres from the finger flexors, the anterior tibial muscle, and the calf muscles was recorded intraneurally with tungsten microelectrodes in patients with Parkinsonism with resting tremor and in spastic patients with clonus. During tremor of Parkinsonism, involving the receptor bearing muscles, the Ia afferent fibre discharge patterns were similar to those seen previously in healthy subjects during voluntary fast alternating finger or foot movements: besides the stretch discharges occurring during the relaxation phases, discharges also occurred during the contraction phases. Such contraction discharges, presumed to originate from intrafusal muscle fibre contractions, were not seen in the spastic patients during clonus. During the clonic oscillations each afferent stretch discharge was regularly followed by a stretch reflex contraction which on its falling phase elicited a new volley of impulses in the Ia afferent fibres. The findings are considered to support the notion that, like the contractions in normal voluntary alternating movements, the contractions in tremor of Parkinsonism are organized according to the principle of alpha-gamma coactivation, whereas the contractions in clonus are stretch reflexes causing pure alpha contractions.
The flexion reflex can be elicited via stimulation of skin, muscle, and high-threshold afferents inducing a generalized flexion of the limb. In spinalized animal models this reflex is quite prominent and is strongly modulated by actions of hip proprioceptors. However, analogous actions on the flexion reflex in spinal cord injured (SCI) humans have not yet been examined. In this study, we investigated the effects of imposed static hip angle changes on the flexion reflex in ten motor incomplete SCI subjects when input from plantar cutaneous mechanoreceptors was also present. Flexion reflexes were elicited by low-intensity stimulation of the sural nerve at the lateral malleolus, and were recorded from the ipsilateral tibialis anterior (TA) muscle. Plantar skin stimulation was delivered through two surface electrodes placed on the metatarsals, and was initiated at different delays ranging from 3 to 90 ms. We found that non-noxious sural nerve stimulation induced two types of flexion reflexes in the TA muscle, an early, and a late response. The first was observed only in three subjects and even in these subjects, it appeared irregularly. In contrast, the second (late) flexion reflex was present uniformly in all ten subjects and was significantly modulated during hip angle changes. Flexion reflexes recorded with hip positioned at different angles were compared to the associated control reflexes recorded with hip flexed at 10°. Hip flexion (30°, 40°) depressed the late flexion reflex, while no significant effects were observed with the hip set in neutral angle (0°). Strong facilitatory effects on the late flexion reflex were observed with the hip extended to 10°. Moreover, the effects of plantar skin stimulation on the flexion reflex were also found to depend on the hip angle. The results suggest that hip proprioceptors and plantar cutaneous mechanoreceptors strongly modulate flexion reflex pathways in chronic human SCI, verifying that this type of sensory afferent feedback interact with spinal interneuronal circuits that have been considered as forerunners of stepping and locomotion. The sensory consequences of this afferent input should be considered in rehabilitation programs aimed to restore movement and sensorimotor function in these patients.
Cutaneous afferents; Flexion reflex; Hip proprioceptors; Rehabilitation; Sensorimotor integration
patients were studied to understand whether stance unsteadiness is
associated with changes in the control of voluntary force, muscle tone,
or reflex excitability, rather than to abnormal posture connected to
the motor deficit itself.
normal subjects, 12 patients affected by amyotrophic lateral sclerosis
(ALS), seven by spastic paraparesis, and 14 by hemiparesis were
studied. All patients featured various degrees of spasticity and
paresis but were free from clinically evident sensory deficits. Body
sway during quiet upright stance was assessed through a stabilometric
platform under both eyes open (EO) and eyes closed (EC) conditions. The
sudden rotation of a supporting platform, in a toe up and toe down
direction respectively, evoked short (SLR) and medium latency (MLR)
reflex responses to stretch of the soleus or the tibialis anterior (TA) muscle.
was found between clinical findings (tone, muscle strength, tendon
reflexes, plantar response, and duration of disease) and body sway. On
average, all patient groups exhibited a forward shift of the centre of
foot pressure (CFP) with respect to normal subjects; in addition,
paraparetic and to a much larger extent hemiparetic patients showed a
lateral shift of CFP. Body sway area was significantly increased only
in the hemiparetic patients. No relation was found between position of
the CFP and sway within any patient group. Soleus SLR was increased in
all patients with respect to normal subjects. TA SLR was often seen in
both patients with ALS and paraparetic patients, but only rarely in
normal subjects and hemiparetic patients. However, no relation was
found between amplitude of soleus or TA SLRs and stabilometric variables. The frequency and size of soleus MLR and TA MLR were decreased in all patients. These responses were decreased in size and
not modulated by background EMG in the affected leg of hemiparetic patients, suggesting a disturbed control of spinal reflexes fed by
spindle group II afferent fibres.
proposed that body posture, paresis, or monosynaptic reflex
hyperexcitability do not affect the control of equilibrium during quiet
upright stance. In hemiparetic patients, the decreased amplitude of
MLRs might be the main cause of the large postural instability. The
results are congruent with the hypothesis of a role for group II
afferent input in the reflex control of equilibrium.
The contribution of the fusimotor system to reflex reinforcement such as the Jendrassik manoeuvre was investigated by recording single unit activity with tungsten electrodes from muscle spindle afferent nerves in unanaesthetized normal human subjects. Muscle spindle afferent activity was recorded before, during, and after the reinforcement test. When the leg muscles remained relaxed during the Jendrassik manoeuvre, spindle activity recorded in the tibial nerve was accelerated. Also in the median nerve, activity from muscle spindle afferent fibres was increased during a remote contraction of the ipsilateral quadriceps muscle. Comparing the time course of the phasic reflex reinforcement and the muscle spindle facilitation during the remote contraction, a marked after-effect was recorded in both responses. Present results show an increased spontaneous muscle spindle activity in relaxed muscles during a remote muscle contraction, and provide evidence for the contribution of the fusimotor system to the enhancement of phasic reflexes by reinforcement manoeuvres.
Ih, which influences neuronal excitability, has recently been measured in vivo in sensory neuron subtypes in dorsal root ganglia (DRGs). However, expression levels of HCN (hyperpolarization-activated cyclic nucleotide-gated) channel proteins that underlie Ih were unknown. We therefore examined immunostaining of the most abundant isoforms in DRGs, HCN1 and HCN2 in these neuron subtypes. This immunostaining was cytoplasmic and membrane-associated (ring). Ring-staining for both isoforms was in neurofilament-rich A-fiber neurons, but not in small neurofilament-poor C-fiber neurons, although some C-neurons showed cytoplasmic HCN2 staining. We recorded intracellularly from DRG neurons in vivo, determined their sensory properties (nociceptive or low-threshold-mechanoreceptive, LTM) and conduction velocities (CVs). We then injected fluorescent dye enabling subsequent immunostaining. For each dye-injected neuron, ring- and cytoplasmic-immunointensities were determined relative to maximum ring-immunointensity. Both HCN1- and HCN2-ring-immunointensities were positively correlated with CV in both nociceptors and LTMs; they were high in Aβ-nociceptors and Aα/β-LTMs. High HCN1 and HCN2 levels in Aα/β-neurons may, via Ih, influence normal non-painful (e.g. touch and proprioceptive) sensations as well as nociception and pain. HCN2-, not HCN1-, ring-intensities were higher in muscle spindle afferents (MSAs) than in all other neurons. The previously reported very high Ih in MSAs may relate to their very high HCN2. In normal C-nociceptors, low HCN1 and HCN2 were consistent with their low/undetectable Ih. In some C-LTMs HCN2-intensities were higher than in C-nociceptors. Together, HCN1 and HCN2 expressions reflect previously reported Ih magnitudes and properties in neuronal subgroups, suggesting these isoforms underlie Ih in DRG neurons. Expression of both isoforms was NT3-dependent in cultured DRG neurons. HCN2-immunostaining in small neurons increased 1 day after cutaneous inflammation (CFA-induced) and recovered by 4 days. This could contribute to acute inflammatory pain. HCN2-immunostaining in large neurons decreased 4 days after CFA, when NT3 was decreased in the DRG. Thus HCN2-expression control differs between large and small neurons.
Two factors, the ETS transcription factor ER81 and skeletal muscle-derived neurotrophin-3 (NT3), are essential for the formation of muscle spindles and the function of spindle afferent–motoneuron synapses in the spinal cord. Spindles either degenerate completely or are abnormal, and spindle afferents fail to project to spinal motoneurons in Er81 null mice; however, the interactions between ER81 and NT3 during the processes of afferent neuron and muscle spindle development are poorly understood. To examine if overexpression of NT3 in muscle rescues spindles and afferent–motoneuron connectivity in the absence of ER81, we generated myoNT3;Er81−/− double-mutant mice that selectively overexpress NT3 in muscle in the absence of ER81. Spindle reflex arcs in myoNT3;Er81−/− mutants differed greatly from Er81 null mice. Muscle spindle densities were greater and more afferents projected into the ventral spinal cord in myoNT3;Er81−/− mice. Spindles of myoNT3;Er81−/− muscles responded normally to repetitive muscle taps, and the monosynaptic inputs from Ia afferents to motoneurons, grossly reduced in Er81−/− mutants, were restored to wild-type levels in myoNT3;Er81−/− mice. Thus, an excess of muscle-derived NT3 reverses deficits in spindle numbers and afferent function induced by the absence of ER81. We conclude that muscle-derived NT3 can modulate spindle density and afferent–motoneuron connectivity independently of ER81.
muscle spindles; sensory neurons; motor neurons; neurotrophins; NT3; ETS transcription factors; ER81; mutant mice
Spinal reflex excitability study in sensory–motor incomplete spinal cord-injured (SCI) and spinal intact subjects.
To investigate the effects of plantar cutaneous afferent excitation on the soleus H-reflex and flexion reflex in both subject groups while seated.
Rehabilitation Institute of Chicago and City University of New York, USA.
The flexion reflex in SCI subjects was elicited by non-nociceptive stimulation of the sural nerve. In normal subjects, it was also elicited via innocuous medial arch foot stimulation. In both cases, reflex responses were recorded from the ipsilateral tibialis anterior muscle. Soleus H-reflexes were elicited and recorded via conventional methods. Both reflexes were conditioned by plantar cutaneous afferent stimulation at conditioning test intervals ranging from 3 to 90 ms.
Excitation of plantar cutaneous afferents resulted in facilitation of the soleus H-reflex and late flexion reflex in SCI subjects. In normal subjects, the soleus H-reflex was depressed while the late flexion reflex was absent. The early flexion reflex was irregularly observed in SCI patients, while in normal subjects a bimodal reflex modulation pattern was observed.
The effects of plantar cutaneous afferents change following a lesion to the spinal cord leading to exaggerated activity in both flexors and extensors. This suggests impaired modulation of the spinal inhibitory mechanisms involved in the reflex modulation. Our findings should be considered in programs aimed to restore sensorimotor function and promote recovery in these patients.
foot sole; flexion reflex; soleus H-reflex; rehabilitation; sensorimotor integration; SCI
SUMMARY AND CONCLUSIONS
Whole cell patch-clamp recordings were obtained from identified cutaneous and muscle afferent neurons (33-60 μm diam) in dissociated L4 and L5 dorsal root ganglia (DRGs) from normal rats and from rats 2-3 wk after sciatic nerve ligation or crush injury. γ-Aminobutyric acid (GABA)-induced conductance was compared in normal and injured neurons from both functional classes of sensory neurons.Control cutaneous afferent neurons had a peak GABA-mediated conductance of 287 ± 27 (SE) nS compared with 457 ± 42 nS for control muscle afferent neurons.An inflection on the downslope of the action potential was observed in 47% of cutaneous afferent neurons compared with 20% of muscle afferent neurons.After ligation and transection of the sciatic nerve there was no change in the GABA-mediated conductance of muscle afferent neurons or in the action potential waveform (23% inflected). However, the cutaneous afferent neurons displayed a greater than twofold increase in their GABA-mediated conductance and displayed a prominent reduction in the number of neurons with inflected action potentials ( 13% inflected). Input resistance was similar in cutaneous and muscle afferent neurons and decreased after ligation in cutaneous but not muscle afferents. Resting potential averaged from −50 to −56 mV in normal and ligated groups for both cutaneous and muscle afferent neurons.After crush injury in cutaneous afferent neurons where the transected axons were allowed to regenerate into the distal nerve stump, GABAA-receptor-mediated conductance was elevated compared with controls. However, action potential waveform was not altered by crush injury, suggesting a differential regulation of these two properties in cutaneous afferent neurons.These data indicate that injury-induced plasticity of GABAA-receptor-mediated conductance and action potential waveform occurs in cutaneous but not muscle afferent DRG neurons. It appears that peripherally derived influences are critical in maintaining the electrophysiological phenotype of cutaneous afferent neurons but not muscle afferent neurons.