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Stiff-man syndrome is a disease of sporadic occurrence. An autoimmune pathogenesis is thought to involve the spinal interneuronal circuits, resulting in isolation of the motor neurons from their inhibitory influence1. Most of the reported cases have been in adults.
A boy aged 11 was seen because of intermittent stiffness and painful spasms of the limb muscles with difficulty in walking of 5 years' duration, all of which worsened after taking a few steps (Figure 1). There was no family history of a similar illness. On examination there was an exaggerated lumbar lordosis. Mental functions and cranial nerves were normal. There was no demonstrable muscle weakness. On palpation of his thighs and calves the muscles felt firm and were tender. They would suddenly stiffen when touched or during a startle induced by a loud sound. The muscles around the forearm, knee and ankle would stiffen with twisted posturing and the patient would find it impossible to move these joints until the spasm subsided. This resulted in an awkward posture and a clumsy wide-based gait when he was asked to walk a few steps. The trunk muscles were little affected. He could not get up from the squatting position, since any activity aggravated the painful spasms. All the deep tendon reflexes were brisk. There was no clinical evidence of either peripheral nerve or spinal cord disease. Autonomic and sphincter function were normal. No myoclonus was ever noticed.
The following were within normal limits: routine haematological tests, thyroid function, antinuclear antibody, anti-double-stranded DNA antibody, blood glucose, serum lactate (pre and post exercise), liver function, serum copper and serum ceruloplasmin. Nerve conduction was normal but needle electromyography showed continuous motor unit activity (CMUA) at rest and complete disappearance of motor activity with intravenous administration of diazepam (Figure 2). CMUA was seen in the gastrocnemius, quadriceps and abductor pollicis brevis muscles.
He was started on oral diazepam 2 mg thrice daily (body weight 19.5 kg). Before treatment he could walk 4-5 m on a level floor and was then halted by painful spasms. After 5 days of diazepam, the stiffness and spasms were much less severe and he could walk 40-50 m without difficulty. In addition he could get up from the squatting position. He was discharged on the same dose of diazepam, now able to perform activities of daily living with little discomfort.
The diagnosis in this patient was based on the clinical features of stimulus-sensitive and activity-induced painful muscle spasms in association with continuous motor unit activity seen on the EMG. The pattern of muscles involved was consistent with the stiff-limb syndrome described by Barker et al.2, and the response to diazepam strengthened the diagnosis. Differential diagnoses such as myotonia, pseudomyotonia, myokymia, neuromyotonia, paroxysmal kinesigenic dystonia, paroxysmal exertion-induced dystonia, extrapyramidal syndromes, pyramidal dysfunction, tetanus, hyperexplexia, spinal cord disorders and reflex sympathetic dystrophy were considered and excluded.
Various subgroups of the stiff-man syndrome have been described2. Progressive encephalomyelitis with generalized rigidity4 usually manifests as part of a paraneoplastic syndrome. It invariably follows a progressive and unrelenting course leading to death within a few months. Stiff-trunk (man) syndrome associated with autoantibodies5 is characterized by rigidity predominantly of the neck, trunk and proximal leg muscles, painful spasms of axial muscles and lumbar hyperlordosis. This is the commonest presentation. Typically, the upper limbs, distal lower limbs, sphincters and cranial nerves are spared. Almost all patients have antibodies to glutamic acid decarboxylase in blood and cerebrospinal fluid. Some also have antibodies to pancreatic beta-cells, thyroid cell microsomes, gastric parietal cells and smooth muscle cells6. A stiff-man syndrome associated with malignancies7,8 has been described in patients with breast and small-cell lung carcinomas. These patients have antibodies to a synaptic vesicle protein, amphiphysin. Stiff-limb syndrome2 is characterized by rigidity and abnormal postures of the legs with painful spasms. The trunk is less involved. The sphincters and the brainstem are involved in many patients. A few of these patients have antibodies to glutamic acid decarboxylase. There have been reports of patients with associated generalized myoclonus9, also called jerking stiff-man syndrome, possibly a subgroup of this variety.
Autoantibodies are typically present in the stiff-trunk subgroup, but are occasionally seen in the stiff-limb variety too. Therefore, insulin-depéndent diabetes, anaemia, and other associated autoimmune manifestations are more common in the former.
The most striking aspect of this patient is the onset at age 6, since most reports have been on adults. Familial stiff-man syndrome has been described with rigidity and muscle spasms inherited in an autosomal dominant pattern10, but this childhood case seems to have been sporadic.