Neuromuscular findings in thyroid dysfunction: a prospective clinical and electrodiagnostic study

Objectives—To evaluate neuromuscular signs and symptoms in patients with newly diagnosed hypothyroidism and hyperthy-roidism. Methods—A prospective cohort study was performed in adult patients with newly diagnosed thyroid dysfunction. Patients were evaluated clinically with hand held dynamometry and with electrodiagnosis. The clinical features of weakness and sen-sory signs and the biochemical data were evaluated during treatment. Results—In hypothyroid patients 79 % had neuromuscular complaints, 38 % had clinical weakness (manual muscle strength testing) in one or more muscle groups, 42 % had signs of sensorimotor axonal neuropathy, and 29 % had carpal tunnel syndrome. Serum creatine kinase did not correlate with weakness. After 1 year of treatment 13 % of the patients still had weakness. In hyperthyroid patients 67 % had neuromuscular symptoms, 62% had clinical weakness in at least one mus-cle group that correlated with FT4 con-centrations, but not with serum CK. Nineteen per cent of the patients had sensory-motor axonal neuropathy and 0% had carpal tunnel syndrome. The neuro-muscular signs developed rapidly, early in the course of the disorder and were severe, but resolved rapidly and completely dur-ing treatment (average time 3.6 months). Conclusions—Neuromuscular symptoms and signs were present in most patients. About 40 % of the hypothyroid patients and 20 % of the hyperthyroid patients had pre-dominantly sensory signs of a sensorimo-tor axonal neuropathy early in the course of thyroid disease. Weakness in hyperthy-roidism evolved rapidly at an early stage of the disorder and resolved completely during treatment, suggesting a functional muscle disorder.Hand held dynamometry is sensitive for the detection of weakness and for the clinical evaluation of treat-ment eVects. Weakness in hypothyroidism is more diYcult to treat, suggesting myopathy