Hand Dystonia

Original Editor - Arnold Fredrick D'Souza
Top Contributors - Arnold Fredrick D'Souza, Ewa Jaraczewska and Kim Jackson

Introduction

Dystonia Medical Research Foundation defines hand dystonia as a focal dystonia characterized by excessive, involuntary muscle contractions in the fingers, hand, forearm, and sometimes shoulder.

Etiology

Genetic predisposition and environmental factors like repetitive stress in the form of frequent complex motor tasks have been associated with the pathogenesis of hand dystonia.

Pathophysiology

There are multiple nervous system dysfunctions that have been identified in patients with hand dystonia. These include:

Abnormal inhibitory mechanisms

Abnormal inhibition is seen at multiple levels of the nervous system which includes the lack of reciprocal inhibition, impaired intracortical inhibition in both hemispheres, and dysfunction of the 'surround inhibition' mechanism (selective control of individual muscles by simultaneous inhibition of surrounding muscles).

Abnormal sensory function

At any given site, a history of pain or abnormal sensation commonly precedes the onset of motor symptoms. Abnormal sensory gating (modulation of sensory processing in response to movement) and somatotopic organization leads to abnormal sensorimotor integration.

Aberrant neuroplasticity

Uncontrolled neuroplasticity reorganizes the cortical sensorimotor maps which give rise to symptoms of hand dystonia.

Clinical Presentation

Primary focal upper extremity dystonia

Initially, there will be marked tightness in muscles responsible for the action being performed. It is followed by the involvement of surrounding muscles. This causes abnormal movements characteristic of dystonia which may worsen with prolonged activity of the involved muscles. Common examples include writer’s, typist’s, or musician’s cramp and golfer’s yips. These might initially appear to be task-specific dystonias and may progress over time into being less specific.

Patients usually present with abnormal upper limb posturing. Excessive finger and wrist flexion, forearm pronation, and humeral abduction are the most common findings. Although symptoms may first appear unilaterally, disease progression may lead to the involvement of both extremities. Some patients report pain and discomfort in the affected extremity.

Generalized dystonia presenting as focal dystonia

They include primary childhood-onset dystonias, dopa-responsive dystonia and dystonia due to a chromosome 9 defect called DYT1.

Secondary dystonia

Hand dystonia may be seen in patients that present with features of other neurological diseases like stroke, Parkinson's disease etc.

Drug-induced dystonia is seen on acute or chronic exposure to antidopaminergic drugs.

Diagnostic Procedures

Electrodiagnostic tests are not diagnostic of hand dystonia. It is a purely clinical diagnosis. This means that a diagnosis is made on the basis of clinically relevant history and physical examination.

Outcome Measures

Arm Dystonia Disability Scale

Tubiana-Chamagne Scale (used for Musician's dystonia)

Writer's Cramp Rating Scale

Management

Pharmacological management

Oral medications like levodopa, muscle relaxants, anticholinergics, benzodiazepines, antipsychotics, anti-epileptics, and tricyclic anti-depressants show limited benefits.

Botulinum toxin injection of forearm muscle groups (flexor, extensor or both) has shown improvement in hand function.

Surgical management

Stereotactic thalamotomy and thalamic deep brain stimulation have been effective.

Neurorehabilitation

Biofeedback, motor training, self-guided exercises, and modified pen grips are effective in the management of hand dystonia. A combination of occupational therapy and botulinum toxin injection showed greater benefit when compared to injection alone.

Studies have investigated the use of non-invasive brain stimulation. Repetitive transcranial magnetic stimulation of the primary motor cortex, premotor and supplementary motor area has shown improvements in hand function. Transcranial direct current stimulation of the cerebellum improved motor control.

Significant improvements have also been seen with the application of TENS.

Differential Diagnosis

The differential diagnosis of hand dystonia includes the following:

1. Neuropathies, radiculopathies or plexopathies of the upper extremity
2. Complex regional pain syndrome
3. Repetitive stress injury
4. Focal seizures
5. Thoracic outlet syndrome
6. Effects of medication
7. Psychogenic movement disorders

Resources

Hand Dystonia - Dystonia Medical Research Foundation

Arm Dystonia Disability Scale

Tubiana-Chamagne Scale

Writer's Cramp Rating Scale