Although functional alterations in the central nervous system (CNS) and peripheral nerves are well documented in overt hypothyroidism, little is known about alterations of CNS in acute hypothyroidism. Sixteen patients with differentiated thyroid carcinoma were studied when prepared for radioiodine scanning after stopping levothyroxine (LT 4 ) therapy for 6 weeks to determine whether acute hypothyroidism leads to alteration in brainstem auditory evoked potentials (BAEPs). Repeat BAEPs were performed on the same patients at 6 months of the following L-T 4 therapy when patients were eu-thyroid. Neurophysiological findings were compared with a group of 20 normal controls with no hystory of thyroid disease. Wave I latency and I-III, III-V and I-V interpeak latencies in BAEPs were studied. A signifiant prolongation of wave I latency found in patients with acute hypothyroidism when com-pared to those in control subjects. Abnormal latencies were not correlated with thyroid hormone levels. These neurophysiologic abnormalities were completely restored to normal at 6 months after L-T 4 therapy. We conclude that acute hypothyroidism leads to reversible alterations in peripheral components of BAEPs. Our results also suggest that BAEPs could be useful tests to monitor functionale alteration of the central nervous system in acute hypothyroidism.

Although functional alterations in the central nervous system (CNS) and peripheral nerves are well documented in overt hypothyroidism, little is known about alterations of CNS in acute hypothyroidism. Sixteen patients with differentiated thyroid carcinoma were studied when prepared for radioiodine scanning after stopping levothyroxine (LT 4 ) therapy for 6 weeks to determine whether acute hypothyroidism leads to alteration in brainstem auditory evoked potentials (BAEPs). Repeat BAEPs were performed on the same patients at 6 months of the following L-T 4 therapy when patients were eu-thyroid. Neurophysiological findings were compared with a group of 20 normal controls with no hystory of thyroid disease. Wave I latency and I-III, III-V and I-V interpeak latencies in BAEPs were studied. A signifiant prolongation of wave I latency found in patients with acute hypothyroidism when com-pared to those in control subjects. Abnormal latencies were not correlated with thyroid hormone levels. These neurophysiologic abnormalities were completely restored to normal at 6 months after L-T 4 therapy. We conclude that acute hypothyroidism leads to reversible alterations in peripheral components of BAEPs. Our results also suggest that BAEPs could be useful tests to monitor functionale alteration of the central nervous system in acute hypothyroidism.