Visual evoked potentials in hypothyroid and hyperthyroid patients before and after achievement of euthyroidism

Thyroid hormone deficiency is frequently associated with central nervous system (CNS) disturbances such as mental retardation, convulsions, coma etc. Studies of quantitative changes in CNS in hypo- or hyperthyroidism are scarce. Evoked potentials is a good method of assessing the electrical response of the brain to different (visual, acoustic, somatosensory) stimuli and has been used extensively in the study of brain disturbances and to a lesser degree in metabolic diseases. We studied the visual evoked potentials (latency and amplitude) in 12 patients with hyperthyroidism and 15 patients with hypothyroidism, before treatment and after they became euthyroid. Four of the hyperthyroids (33%) had abnormally prolonged (> 104 msec) latencies before therapy. Two of them had clinical exophthalmos. No change was observed after euthyroidism was achieved. On the contrary 7 out of 15 (47%) hypothyroids had abnormally prolonged latencies which became normal in 4 when euthyroidism was achieved. Amplitude was lower than normal in 6 and became normal only in one of them after treatment. None of the hyperthyroid patients had amplitude changes. In conclusion, hypothyroid patients may have changes in the amplitude and/or the latency of visual evoked potentials which are reversible to a great extent with thyroxine. Evoked potentials is another method of studying in humans the metabolic effects of thyroxine deficiency in CNS.