Peripheral neuromuscular and central nervous system disorders may occur in both hypothyroidism and hyperthyroidism. Myopathy is the most common of the peripheral neurologic manifestations in both hypothyroidism and hyperthyroidism. The creatine phosphokinase is elevated in only the hypothyroid cases. In hypothyroidism, polyneuropathy also occurs but much less commonly than myopathy. Compressive mononeuropathies, namely carpal tunnel syndrome, are a major feature in hypothyroidism. Myasthenia gravis can be accentuated by either dysthyroid state. Hypothyroidism has been reported to cause an array of additional effects on the neuromuscular junction and muscle. At the level of the central nervous system, psychosis, personality change, mood disorder, confusion, dementia, coma, and seizures can occur in either hypothyroidism or hyperthyroidism. Movement disorders occur in hyperthyroidism, whereas ataxia and headaches are associated with hypothyroidism.