Clinical and electromyographic examination of tremor in patients with thyrotoxicosis.

Tremor is a well-known symptom of thyrotoxicosis, yet no detailed clinical and electromyographic (EMG) examination of it has been published. The aim of this investigation was to establish the clinical and EMG pattern of tremor in patients with thyrotoxicosis and to compare it with the well-known pattern of enhanced physiological tremor caused by anxiety. Twenty-six patients with thyrotoxicosis and tremor and 30 patients with tremor and generalised anxiety disorder were investigated. Tremor was scored clinically in all possible limb positions. EMG examination of tremor activity from antagonist hand muscles was performed. A postural and kinetic tremor with characteristics of an enhanced physiological tremor was found in patients with thyrotoxicosis and generalised anxiety disorder. Tremor involved only the upper limbs in all patients. In conclusion, tremor in thyrotoxicosis and generalised anxiety disorder is an enhanced physiological tremor which cannot be separated clinically or by EMG measurement. Both types of tremor have similar mechanisms and can be distinguished only by the circumstances responsible for their occurrence. Despite only a moderate correlation between tremor intensity and thyroid hormone levels, successful treatment of thyrotoxicosis results in a dramatic improvement of tremor.