eMedicine Specialties > Neurology > Movement and Neurodegenerative Diseases

Writer's Cramp

Jonathan B Strober, MD, Director, Pediatric Muscular Dystrophy Association Clinic; Assistant Clinical Professor, Departments of Pediatrics and Neurology, Division of Child Neurology, University of California at San Francisco
Contributor Information and Disclosures

Updated: Nov 2, 2006

Introduction

Background

Writer's cramp is a form of task-specific focal dystonia. Dystonia is an involuntary, sustained muscle contraction causing twisting movements and abnormal postures; focal dystonia means only one body part is affected. Writer's cramp is the most common dystonia occurring in the setting of repetitive movement disorders. A focal dystonia can sometimes be the first manifestation of a generalized dystonia.

Pathophysiology

Normally, an antagonist muscle relaxes when an agonist muscle is contracted. Patients with dystonia have simultaneous contraction of both groups of muscles. Spinal reciprocal inhibition, a process that inhibits the antagonist muscles when the agonist muscles are active, is reduced in patients with writer's cramp. This is most probably due to aberrant descending commands.

Abnormalities in the basal ganglia lead to abnormalities of sensory processing and motor output. The normal increase in cerebral blood flow in the supplementary motor area is reduced in response to vibration and abnormal somatosensory evoked potentials. These provide evidence for the abnormal sensory processing in patients with dystonia. Increased motor cortex excitability along with decreased cortical inhibition causes abnormal motor output.

Frequency

United States

One study estimated the prevalence to be 69 cases per 100,000 population; this is thought to be an underestimation because a high percentage of patients never seek medical assistance.

International

Again, because of the small percentage of affected patients seeking medical attention, accurate prevalence estimates are not available.

Sex

Prevalence is slightly higher in men; the male-to-female ratio is 1.3:1.

Age

Typically, patients present in the third to fifth decades, and women usually present earlier than men.

Clinical

History

• Incoordination, cramping, and aching of the hand with task-specific movements are usually the initial complaints.
• The hand assumes a semiflexed position of the fingers with possible hyperextension of the fingers and hyperflexion or extension of the wrist with supination or pronation.
• The symptoms become exaggerated with attempts to perform a specific task, such as writing. In some cases, the hand may dart across the page with a sudden jerk.
• A related condition is primary writing tremor. Affected individuals exhibit a prominent large-amplitude tremor only with writing.

Physical

• Neurologic examination findings are usually normal.
• Subtle findings include mild dystonic postures developing either spontaneously or with movement and reduced arm swing.
• One third of patients have a tremor in the affected arm or hand while writing or when the extremity is outstretched. Observation of the limb during writing is an important part of the examination; the assumption of dystonic postures should be demonstrable. Patients affected with primary writing tremor, a variant of writer's cramp, may exhibit a large-amplitude tremor only during writing. In contrast to essential tremor, action or sustentation tremors are not seen with other tasks such as holding a full cup of liquid or coordination testing. Dystonic posturing is usually not seen with this condition.

Causes

• Writer's cramp frequently affects persons who write a great deal or perform other repetitive hand movements such as typing.
• Approximately 5% of patients have a positive family history of a similar condition.
• Five to ten percent report an accident or injury to the hand or arm immediately preceding the onset of symptoms.
• Several possible, but rare, associations have been reported, including C6 ruptured disk, lithium use, basal ganglia or cortical tumors, arteriovenous malformations (AVMs), and stroke. However, most cases are idiopathic.

References

• Dopamine-Responsive Dystonia
• Multiple Sclerosis
• Parkinson Disease
• Wilson Disease