The neurologic disorders associated with thyroid dysfunction span the entire spectrum of neurology. Symptoms range from disorders of emotion and higher cognitive function to movement disorders, neuromuscular diseases, and a range of rarer yet significant neurologic sequelae.
Generally, the subject may be divided into the effects on the metabolism and development of neurologic structures in situations of intoxication or deprivation of thyroid hormones. Hyperthyroidism prominently causes neuropsychiatric abnormalities, neuromuscular disease, and a range of other disorders, such as dysthyroid orbitopathy, movement disorders, and neuropathies. Hypothyroidism has more significant effects on the developing brain, leading to long-lasting effects of congenital hypothyroidism. It also has a wide range of effects in the adult, including psychomotor slowing, neuropsychiatric disease, metabolic effects that can lead to seizures, encephalopathy, and coma, and neuromuscular disorders, such as myopathy and neuropathy. It is also associated with cerebellar ataxia, myasthenia gravis, and sleep apnea.
The wide-ranging effects of thyroid hormone excess and depletion on the neurologic system have been given focus by recent advances in the understanding of the cellular and molecular effects of this important chemical. There is still much to understand and elucidate, particularly in the area of neuropsychiatric morbidity and cognitive change.
(THE NEUROLOGIST 7:147-157, 2001)