The usual age of onset of task-specific dystonias spans the third to sixth decade.13,14
Initial symptoms may include a feeling of painless tightness, fatigue, and lack of dexterity with subsequent development of uncontrollable activation of surrounding muscles and abnormal movements during a specific, highly skilled motor task. Other activities requiring the same muscles may be performed normally, at least initially.13
Tremor in the affected body parts may also occur particularly during the inciting task in as many as half of the patients.15
We will now review the phenomenology of the most common task-specific dystonias after a craniocaudal anatomical distribution.
Lower facial muscles may be involved in task-specific dystonias. “Embouchure” is a musical term to describe the interface between facial muscles and the mouthpiece of a woodwind or brass instrument needed to control airflow to the instrument. The coordinated and highly specific activation of each muscle involved is fundamental for the creation of proper pitch and volume with the musical instrument. Embouchure dystonia is a task-specific dystonia that affects these facial muscles.16
The average age of onset is in the fourth decade, and symptoms typically begin an average of 25 years (range, 7–45 years; standard deviation, 13 years) after starting to learn the instrument. Initial symptoms were usually limited to one range of notes or style of playing, but this tended to progress to other sounds and even to non–task-specific movements. Patients complained of mouth tremor, lip fatigue, abnormal jaw opening, and excessive and incomplete lip closure. However, facial pain was uncommon (12%). Frucht et al.
classified embouchure dystonia into embouchure tremor, involuntary lip movements, and jaw movement abnormalities. About 10% of the patients described by Frucht had a hand task–specific dystonia, which preceded the embouchure dystonia by as many as 19 years.17
Embouchure dystonia may spread in about 25% of patients to involve other facial muscles.16
Once present, embouchure dystonia does not usually remit and responds only poorly to pharmacologic interventions and chemodenervation. Prognosis is therefore poor, and most patients cannot earn a living playing their instrument.
The next part of the body affected by task-specific dystonia is the larynx. Although the laryngeal dystonias are not typically considered task-specific dystonias, they do meet our criteria because excessive muscle activity occurs only with selected vocal tasks. Laryngeal dystonia affects the quality and strength of voice. The two main forms are adductor laryngeal dystonia and the less common abductor laryngeal dystonia. The adductor type produces tight, strained, strangled speech due to excessive adduction of the vocal cords. Voice is typically worse with speaking and much better with whispering, singing, talking while yawning, shouting, or changing pitch. Voice produced in connected speech compared with sustained vowels may provoke more frequent and severe laryngeal spasms, and this task specificity may help differentiate adductor dystonia from other laryngeal conditions.18
Breathing is almost always normal.21–23
Abductor laryngeal dystonias, characterized by excessive breathiness, seem even more task specific with worse function with voiceless consonants (p, t, l, s, f, h, th). Sounds, such as “s,” “h,” or “k,” preceding open vowels in words like “coffee” and “cake” usually are affected most.19
But many patients can perform these sounds normally while singing, laughing, humming, shouting, yawning, or just by changing the pitch of the speech.19
The risk of spread in laryngeal dystonias is relatively low (12%).4
Laryngeal dystonias can be disabling, depending on the patience’s reliance on voice for working. Laryngeal dystonias are three times more common in females, and the average age of onset is in the fifth decade.19
We found only one clearly task-specific cervical dystonia case report.20
This patient had bilateral arm amputations and learned to write and draw by holding a pen with his mouth. After 20 years of frequent and extensive writing, he developed slowly progressive cervical dystonia. Initially, symptoms were present only while writing, but after more than 10 years these progressed to be present constantly and without relationship with the initial inciting task.
Upper extremity task-specific dystonias include a wide variety of disorders, many related with labor, including shoemaker’s dystonia, tailor’s dystonia, pianist’s cramp, writer’s cramp, and hairdresser and telegraphist’s cramps. Upper extremity task-specific dystonias related to sports include the golfer’s yips,21,22
pistol shooter’s cramp,23
and petanque player’s arm dystonia.24
We will now review the clinical manifestations of the most common task-specific dystonias of the upper extremities.
Writer’s cramp is a task-specific dystonia of writing, characterized initially by an abnormally tight grip while writing with progressive difficulty in performing the task as writing continues. Usually distal muscles of the dominant hand are the first affected. Tight grip of the pen is typical, and hand–wrist flexors are more commonly involved than extensors, even though hyperextension of the distal phalanges or even the fingers has been seen.13
Excessive muscle spasms may progress to more proximal muscles around the elbow and shoulder, producing abduction of the arm. Symptoms appear at a mean age of 38 years and may be painless or accompanied by painful hand and forearm cramping.25
Slowly, handwriting becomes less legible. Sensory tricks such as rubbing the back of the hand may diminish writer’s cramp. An initial classification divided the patients in two groups, simple and dystonic writer’s cramp, on the basis of the absence or presence of dystonia while performing other tasks.13
However, about half of the patients with simple cramps progress to having dystonia with other activities. About a third of patients with writer’s cramp have intermittent symptoms that are not disabling. However, the rest have constant abnormal writing that can become illegible. Remissions are uncommon, and symptoms can progress to the other hand.4,13,25
Some general features that are associated with poor prognosis include secondary dystonia, tremor, and long-duration or progressive symptoms.26
Typist’s cramp is a task-specific dystonia characterized by excessive flexion or extension of the fingers that produces slow and laborious typing. Hand and wrist pain while typing is common. Excessive finger extension can be either the primary abnormality or a compensatory behavior. Excessive thumb flexion has also been reported.13
Golfer’s cramp, or the yips, may be a task-specific dystonia. The yips are manifested by symptoms of jerks, tremors, or freezing in the hands and forearms mostly while putting. These symptoms impair golf performance and contribute to attrition in golf. Many yips-affected golfers decrease their playing time or quit to avoid exposure to this embarrassing problem. If this is the main physical activity that the patient is performing, this could lead to depression and sedentary life–related comorbidities. Early studies demonstrated a lack of psychopathology in these patients.27
Adler et al.
evaluated the neurophysiological characteristics of the excessive motor activation that impairs function and found evidence of cocontraction on affected golfers and not in control subjects.28
The yips may be classified into two different types, dystonic (type I) and anxiety related (type II).29
Musicians practice and perform highly skilled motor tasks that may lead to development of focal hand dystonias specific to playing the relevant instrument such as piano, guitar, clarinet, flute, horn, harp, and the tabla.30,31
Both professional and amateur players are at risk.17
The mean age of presentation is in the fourth decade.32–34
Musician’s task-specific dystonias rarely occur during the initial training period but rather more commonly develop at the peak professional stage.17
Sensory complaints are rare.32
The most commonly affected muscles are those heavily involved in the performance and most often in the hand that performs the most demanding tasks.37,32,34
In pianists, the right hand is more commonly involved, typically with fourth and fifth finger excessive flexion, which are the same fingers affected on the left hand of violin players.33
If the bowing hand of violinists is affected, then it is usually associated with abnormalities of wrist posture.14
The right hand is more commonly involved on guitarists. This lateralization is not as prominent in woodwind players, probably owing to the equivalent complexity of movements in both hands.17
Whereas guitar players have a hyperflexion of the third right finger, clarinetists tend to have hyperextension.33
Some musicians have task-specific dystonias while playing one instrument but not while playing others. The prognosis is poor for musician’s cramp because these task-specific dystonias impair performance, forcing as many as half of musicians to stop professional playing.35
Prognosis may be worse for string players who have dystonia of the bowing arm because treatment is less effective.36
Task-specific dystonias of the lower extremities are rare. For example, children with DYT1 dystonia may begin with foot dystonia only when walking forward that is not present when walking backward or while running or swimming. However, this specificity is often lost as the condition progresses. There are some reports of lower extremity task-specific dystonias. In one, a patient had walking-induced equinovarus deformity only when the leg was at the end of the swing phase.37
Lo and Frucht reported two cases of patients who had dystonia of the lower extremities only while walking down steps.38
An interoceptive sensory trick (imagining walking in a different modality) led to temporary improvement. Some adult-onset primary lower limb dystonia can be relatively task specific and be present only during walking or running but not while standing or sitting.39,40