AUDITORY BRAIN-STEM RESPONSES IN THYROID-DISEASES BEFORE AND AFTER THERAPY

The aim of this study was to evaluate through the auditory brainstem r esponses (ABRs) the electrical events generated along the auditory pat hway in 56 adult patients affected with hyper- and hypothyroidism. Twe nty-four normal-hearing hyperthyroid patients affected with Graves' di sease and 32 normal-hearing hypothyroid patients (9 with subclinical a nd 23 with overt hypothyroidism) were subjected to standard (clicks at 21 pps) and sensitized ABR with masking wide-band (masking noise). In addition, thyroid scintiscan and ultrasonography, free T-3 and T-4, t otal T-3 and T-4, TSH, antimicrosomal and antithyroglobulin antibodies , audiogram and impedance tests were performed in all the patients. Th is study was repeated after 6-12 months of treatment in conditions of euthyroidism. The results showed changes of ABRs both in the standard procedure as well as in the sensitized test in 6 hyperthyroid (25%) an d 8 hypothyroid patients (25%). Ah the patients with abnormal ABRs had overt hypothyroidism (8/23; 34,7%). The ABRs became normal in 5 out o f 6 Graves' patients after 6-12 months of methimazole treatment. ABRs remained abnormal in all the hypothyroid patients despite their having been on L-thyroxine treatment for 6-12 months and were euthyroid for at least 5 months before the study was repeated. These findings sugges t that ABR abnormalities are indicative only of a nonspecific injury i n the bulbo-ponto-mesencephalic centers. Alterations of ABRs in thyroi d diseases are not specific in relation to hyper- or hypothyroidism. L astly, there is a relationship between ABR abnormalities and the degre e of hypothyroidism, even if ABR alterations are not always reversible after long-term therapy.