Joel M. Rothfeld, MD, PhD

Disclosures

May 02, 2003

Question

What is the best medical treatment for writer's cramp? Is botulinum toxin injection the preferred treatment? What about the evidence for other treatment options?

Response from Joel M. Rothfeld, MD, PhD

In general, dystonias are sustained contractions of muscle groups that can involve cranial, cervical, or upper limb muscles. Dystonic movement is characterized by sustained contraction of a muscle group or the manifestation of a jerky, tremulous appearance of the muscle group affected. Focal dystonias are typically adult-onset and nonhereditary. Examples of focal dystonias include torticollis and sustained contraction of either sternocleidomastoid muscle that can cause persistent neck turning contralateral to the muscle involved. Another focal dystonia is writer's cramp.

In writer's cramp, involuntary contraction of intrinsic hand and forearm musculature impairs fine motor control of the hand when writing. The sustained flexion of the fingers results in impaired fine motor control and illegible handwriting. Typically, the act of writing provokes involuntary extension of the thumb and hyperextension of the index finger. The actual etiology of writer's cramp is unknown. However, it has been clearly established that the cramping of the muscles involved is secondary to a central nervous system disorder (such as a derangement in sensory feedback to motor areas in the brain) involving the basal ganglia structures, and is not a primary muscle disorder.

Some of the adult-onset focal dystonias are genetically based, with increasing recognition of allelic involvement in dystonia.

Treatment of dystonias was difficult until the development of botulinum toxin therapy. Some forms of dystonia show L-dopa responsiveness, although the degree of response is usually only partial. High-dose anticholinergic therapy has provided some benefit, as has baclofen, beta-blocking agents, and benzodiazepines. However, use of these oral medications is sometimes limited because of unacceptable side effects and limited efficacy.

Botulinum toxin provides a specific intervention at the end-organ site -- the involved musculature. Temporary paralysis of the neuromuscular junction successfully reduces the sustained neuronal input to muscles involved, and thereby lessens the tone of the muscle groups and allows for some functional movement.

The diagnosis of a focal dystonia, such as writer's cramp, is initially considered by observing the abnormal posturing of the hand musculature that prevents writing. Typical work-up should include brain imaging studies to rule out stroke or other structural etiologies, as well as serologic work-up to rule out treatable causes such as Wilson's disease (check ceruloplasmin and copper levels). Electrodiagnostic studies are sometimes performed to rule out a variant of carpal tunnel syndrome.

Typical EMG-guided delivery of botulinum toxin to the active intrinsic hand musculature that is identified as giving rise to the dystonia has helped restore, to varying degrees, coordinated movement of the dystonic musculature. In some cases, this allows some return of writing function. Of note, it has been shown via PET studies that botulinum toxin does not reverse the cortical dysfunction associated with writer's cramp.

Botulinum toxin is currently the preferred method of treatment for focal dystonias. Its efficacy and safety in this setting have been well established.

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