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Key Words
Hypothyroidism * Cognitive function * Visual-evoked potential * Auditory brainstem response * Event-related potential
Abstract
The purpose of this study is to evaluate objectively the functional changes in the nervous system in hypothyroidism by different electrophysiological parameters and to determine the frequencies of these changes in patients with hypothyroidism. We enrolled 23 patients (17-- 64 years old, mean 38.2) with biochemical evidence of hypothyroidism, with thyroxine less than 4 (mu)g/dI and thyrotropin above 4.5 mU/ml, and 200 age- and sexmatched normal subjects. Detailed clinical examination and electrophysiological measurements included electromyography, motor conduction velocity, visual-evoked potentials (VEPs), brainstem auditory-evoked potentials (BAEPs) and event-related potentials. Determinations of P300, Wechsler Adult Intelligence Scale (IQ) and electroencephalography (EEG) were performed. Of the hypothyroid patients 52% had peripheral nervous system
(PNS) involvement. Entrapment neuropathy was the commonest (35%). Axonal neuropathy was recorded in 9% and myopathy was recorded in another 9%. The central nervous system (CNS) was affected in 78% of the cases. Significant prolongations of P100 latency of VEP, latency and interpeak latency of BAEPs of different waves of hypothyroid patients were compared to the control group. 52% had abnormal VEPs and BAEPs above the mean +/- 2 SD of the normal control group. Six patients (26%) had prolonged P300 latency while 16 patients had an 10 below 90. Eight patients (35%) had EEG changes. Diffuse slowing of background activity was the commonest. No significant correlation was observed between hormonal levels and the different electrophysiological parameters. Thus, the CNS is more vulnerable to the effect of hypothyroidism than the PNS. Therefore, we suggest performing electrophysiological studies in hypothyroid patients, even in the asymptomatic ones, early in the course of disease in order to detect the nervous system involvement.
Copyright 02000 S. Karger AG, Basel
Introduction
Hypothyroidism is associated with characteristic symptoms and signs and functional alterations in many organs and systems [1]. Central (CNS) and peripheral nervous system (PNS) affection may provide the major presenting symptoms [2]. These CNS manifestations include mental retardation, memory changes, depression and rarely convulsions and coma that may occur in 60-80% of the patients [3,4]. Also 60-90% of the patients may have dysfunction of the PNS, e.g. acroparesthesia, weakness and postural imbalance [3]. The metabolic abnormalities, decreased...