What causes Writer's Cramp?

Normally when a muscle contracts an opposing muscle relaxes to allow movement in one direction. In dystonia both the active and opposing muscles contract at the same time with resulting spasm and rigidity of the part. Writer’s cramp tends to occur in a small proportion of people who carry out regular repetitive activities using the hand for fine coordinated movements. Some occupations requiring twisting movements of the fingers or fine assembly of components may also be involved.

The specific cause is not known but abnormalities have been found in the basal nerve ganglia of the brain that appear to interfere with the normal process of transmission of nerve impulses which control muscle tone and coordination of movement. Changes in blood circulation in the motor areas of the brain have also been noted in people exhibiting focal dystonia.

The period of exposure to the specific repetitive task varies greatly between individuals and usually presents at between six months and two years of starting the activity. There is also considerable discrepancy in incidence in similar jobs in different locations with occasional ‘epidemics’ in some areas that are difficult to explain.

At one time there was thought to be a significant psychological element in the cause of writer’s cramp but abnormalities identified in the brain and basal ganglia tend to support a predominantly physical cause. Indeed, most authorities now accept that it is inappropriate to pursue a psychiatric cause for the condition as this may deprive the patient of effective investigation and care by a neurologist. Patients with writer’s cramp do not have a higher incidence of psychiatric disease although there is some evidence of a greater incidence of obsessive personality in those with the condition. Psychological factors may therefore contribute to the effect of the condition.

A small proportion of cases report a history of injury to the arm or hand prior to the onset of symptoms but the mechanism by which this would cause dystonia is not understood.

There have been reports of rare associations of focal dystonia with rupture of the sixth cervical disc, use of lithium medication, tumours affecting the basal ganglia and stroke.