Video 1.
The Phenomenology of Focal Task-specific Dystonia is Demonstrated.
The first segment demonstrates two patients with writer's cramp. A classic pattern of involvement of flexion of the small muscles of the thumb and index finger is seen. The second patient demonstrates a more unusual pattern of extension of the third through fifth fingers. The next patient demonstrates treadmill dystonia, exercise-induced dystonia of the left foot selectively triggered by walking. No evidence of parkinsonism was present on her examination. Abductor dysphonia appears in the next patient, with breathiness and loss of vocal support triggered selectively by words with AA vowel sounds following consonants. The next six patients, all musicians, illustrate the selective involvement of a single finger by dystonia. Two patients each (banjo, flute, and violin) display task-specific dystonic contractions of one finger. The banjo players display dystonic flexion of the right index finger, delaying the timing of plucking the string. The flute players both involve the left pinky, with flexion of the fifth finger's metacarpophalyngeal joint pulling the finger off the instrumental key. The following two violinists both demonstrate a trigger of dystonic flexion of the left ring finger (with some coincident flexion of the pinky as well). Next, two musicians with prominent sensory tricks appear. The first is a traditional Irish accordion player, whose middle finger involuntarily extends off the key while playing. Application of a simple finger splint to the adjacent fourth finger allows him to “bring the third finger back into play” and to use it on the keyboard. Next, a clarinetist with a complex dystonia of the right wrist and finger serendipitously discovered that holding a pencil between his second and third fingers (something he did to facilitate marking the music while practicing), immediately and significantly improved his dystonia. The size and texture of the pencil impacted the efficacy of the trick. The final two segments demonstrate two pianists with isolated task-specific dystonia involving flexion of the index finger. The first shows flexion of the right index finger during performance of a Scarlatti sonata. Four weeks after injection of botulinum toxin into the flexor superficialis of the index finger, there is marked improvement. The last patient demonstrates a plastic brace that he built to prevent flexion of the left index finger during playing. A similar pattern of injections (performed by Dr. David Simpson) markedly improved his dystonia as well.
Table 1
Features of Focal Task-specific Dystonia Discussed by Gowers (G), Duchenne (D), Hammond (H), and Oppenheim (O) Summarized by Topic. ¶ indicates mention by the author
| Category | Specific Feature | G | D | H | O |
|---|---|---|---|---|---|
| Demographic | M>F | ¶ | ¶ | ||
| Age distribution | ¶ | ¶ | |||
| Family history | ¶ | ¶ | ¶ | ||
| Psychiatric comorbidity | ¶ | ¶ | |||
| Natural history | Acute presentations of dystonia | ¶ | |||
| Progression of severity | ¶ | ¶ | |||
| Spread to other tasks with the affected hand | ¶ | ¶ | |||
| Spontaneous remission of symptoms | ¶ | ||||
| Phenomenology | Pure task-specificity of the dystonia | ¶ | ¶ | ||
| Sensory trick | ¶ | ||||
| Sensory trick device used | ¶ | ¶ | ¶ | ||
| Other occupational neuroses (other forms of focal dystonia besides writer's cramp) | ¶ | ¶ | |||
| Sportsman | ¶ | ||||
| Proximal involvement of the affected limb | ¶ | ||||
| Leg dystonia | ¶ | ¶ | |||
| Task-specific torticollis | ¶ | ||||
| Respiratory dysphonia | ¶ | ¶ | |||
| Musicians' hand dystonia | ¶ | ||||
| Musicians' embouchure dystonia | ¶ | ||||
| Etiology | Trauma as trigger of dystonia | ¶ | ¶ | ||
| Task mechanics as causative factor in dystonia | ¶ | ¶ | ¶ | ||
| Instrument as predisposition to develop dystonia | ¶ | ||||
| Mechanism | Central hypothesis of the cause of dystonia | ¶ | ¶ | ¶ | ¶ |
| Idea of motor learning | ¶ | ||||
| Idea of a motor network | ¶ | ||||
| Idea of motor engrams | ¶ | ||||
| Treatment | Idea of prevention of dystonia | ¶ | |||
| Rest as a treatment | ¶ | ¶ | ¶ | ||
| Early treatment as key to response | ¶ | ||||
| Sensory motor retraining protocols | ¶ | ¶ | |||
| Peripheral surgery on the affected limb | ¶ | ¶ | |||
| Limb immobilization as a proposed treatment | ¶ |
Figure 1
A New Working Model of Focal Task-specific Dystonia.
The y-axis represents the stability of the sensory motor network. An elevation in the y-axis depicts the activation energy barrier to be overcome to achieve a new network. Time is represented on the x-axis. Starting from the left side of the graph, factors such as age, training regimen, gender, peripheral biomechanics, family history, and susceptibility to plasticity (surround inhibition) impact the stability of the baseline endophenotype network. A family history of dystonia, male gender, and late age of onset of training push the baseline endophenotype higher on the y-axis, making the network less stable and making an individual more susceptible to develop dystonia. At some point, a peripheral trigger or trauma may push the network up from left to right, over the activation energy barriers (blue hills), resulting in an eventual slide down (orange line) to a meta-stable state of a dystonic prodrome. This dystonic prodrome network is not stable, tending to degenerate (red line) and progressing to the right to a formed dystonic network (far right). Treatments such as sensory motor retraining, limb immobilization, medications, botulinum toxin injections, and stereotactic surgery are aimed at pushing the network from right to left, back up the activation energy scheme (solid blue line with arrows), and in the best-case scenario, returning the patient to a stable non-dystonic network.