Neurologic complications of thyroid dysfunction.

Until such time as results of more rigorous studies are available, the morbidity rates for thyroid dysfunction cited here must suffice. The 1955 to 1956 outpatient "incidence" for England and Wales was 1.1 per 1,000 for thyrotoxicosis and 1.7 per 1,000 for myxedema (18). United States in-patient "incidence" for 1971 was 0.16 per 1,000 for thyrotoxicosis and 0.13 per 1,000 for myxedema (25). The 1935 to 1967 average annual incidence of Graves' disease for females in Olmsted County, Minnesota, was 30.5 per 100,000 (10). Well over 50% of hyperthyroid patients have clinical evidence of mild or moderate muscle weakness. Usually this weakness is proximal, and electro-myography and muscle biopsy confirm the existence of myopathic process (Table 11). Severe muscular weakness of acute onset is relatively rare and is encountered in approximately 1% of hyperthyroid patients (11,17,40). Ophthalmoplegia and psychosis are reported 4% and 2% of patients, respectively (17). Myasthenia gravis, although well publicized, is estimated to occur in less than 1% of patients (3,30). TPP is virtually nonexistent in the West; in the Orient it is reported in 2 to 8% of hyperthyroid patients and is 20 to 60 times more frequent in the hyperthyroid male than in the hyperthyroid female (Table 12). The neurologic symptomatology of myxedema is more extensive, and agreement among the various series is poor. The only unselected series addressing itself to neuromuscular manifestations of myxedema that is suitable for citation is that of Scarpalezos et al. (36). This comprehensive study was done without apparent patient selection, and it reported 2% of patients with definite carpal tunnel syndrome, 6% with myopathy, and 18% with polyneuropathy (Table 13). Reported percentages of hypothyroid patients found to have neurologic manifestations of cerebellar dysfunction are extremely diverse: ataxic gait was reported in 5 to 32% (6,7,12,27) of patients and dysdiadochokinesia in 6 to 52% (7,12,27). Psychosis is encountered in 2 to 5% (6,14,17,27,39) of myxedematous patients, memory loss in 23 to 55% (6,14,27), and coma in less than 1% (27).