Diagnostic and pathophysiological aspects of psychogenic tremors.

Psychogenic tremor has become a rare movement disorder. Twenty-five patients from our movement disorder unit presented either with obviously nonorganic body shaking during stance or with extremity tremors. A sudden onset and a variable but rarely remitting course of the condition was common. The "coactivation sign of psychogenic tremor" and absent finger tremor were the most consistent criteria to separate them from organic tremors. Quantitative analysis of tremor shows decreasing amplitudes in most organic tremors when the extremity is loaded with additional weights. In contrast, we found an increase of tremor amplitude for most of the cases with psychogenic tremor. This might be caused by increased coactivation to maintain the oscillation. These clinical and electrophysiological features suggest a clonus mechanism induced by coactivation as the pathophysiological basis of psychogenic extremity tremor. Psychiatric evaluation did not show overt signs of hysteria for the majority of the patients. However, we found depression and functional somatic or psychosomatic conditions to be frequent among the patients. A reduced ability to cope with stressful situations may play a significant role. The clinical course of the condition is usually far from benign. We conclude that psychogenic tremor can be positively diagnosed by means of neurologic signs in the majority of patients and is not only a diagnosis of exclusion. The poor outcome makes early and serious neuropsychiatric attempts at therapy necessary.