Introduction[edit | edit source]
Etiology[edit | edit source]
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[edit | edit source]
There are multiple nervous system dysfunctions that have been identified in patients with hand dystonia. These include:
Abnormal inhibitory mechanisms[edit | edit source]
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[edit | edit source]
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[edit | edit source]
Clinical Presentation[edit | edit source]
Primary focal upper extremity dystonia[edit | edit source]
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[edit | edit source]
They include primary childhood-onset dystonias, dopa-responsive dystonia and dystonia due to a chromosome 9 defect called DYT1.
Secondary dystonia[edit | edit source]
Drug-induced dystonia is seen on acute or chronic exposure to antidopaminergic drugs.
Diagnostic Procedures[edit | edit source]
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[edit | edit source]
Tubiana-Chamagne Scale (used for Musician's dystonia)
Management[edit | edit source]
Pharmacological management[edit | edit source]
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[edit | edit source]
Stereotactic thalamotomy and thalamic deep brain stimulation have been effective.
Neurorehabilitation[edit | edit source]
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.
Differential Diagnosis[edit | edit source]
The differential diagnosis of hand dystonia includes the following:
- Neuropathies, radiculopathies or plexopathies of the upper extremity
- Complex regional pain syndrome
- Repetitive stress injury
- Focal seizures
- Thoracic outlet syndrome
- Effects of medication
- Psychogenic movement disorders
Resources[edit | edit source]
References[edit | edit source]
- Dystonia Medical Research Foundation. Hand Dystonia. Available from: https://dystonia-foundation.org/what-is-dystonia/types-dystonia/hand-dystonia/ (accessed 17/09/2021)
- Lin PT, Hallett M. The pathophysiology of focal hand dystonia. J Hand Ther. 2009 Apr-Jun;22(2):109-13; 114. doi: 10.1016/j.jht.2008.10.008
- Torres-Russotto D, Perlmutter JS. Focal dystonias of the hand and upper extremity. J Hand Surg Am. 2008 Nov;33(9):1657-8. doi: 10.1016/j.jhsa.2008.09.001
- Gupta N, Pandey S. Treatment of focal hand dystonia: current status. Neurol Sci. 2021 Sep;42(9):3561-3584. doi: 10.1007/s10072-021-05432-7