Subclinical hypothyroidism (SH) refers to an isolated increase of thyroid stimulating hormone (TSH). Cognitive dysfunction has occasionally been reported in patients with SH. The present study aimed to test whether SH affects event-related potentials (ERPs) considered as electrophysiological indices of cognitive processing. We investigated 31 patients with SH (28 females, mean age 52 years) shortly after the detection of SH and without medication. Patients were without any signs of neurological or psychiatric disease. ERPs were elicited using the auditory odd-ball paradigm. On the curves recorded, N1, P2, N2 and P3 components were identified and evaluated in comparison with a group of healthy controls. In SH, latency of P3 was significantly delayed compared with controls (SH: mean 374 ms; controls: 340 ms; p < 0.01). In six SH patients the latency of P3 was abnormal (> Ć + 2SD). Other ERP component latencies did not differ significantly between both groups. In conclusion, ERPs reflect a cognitive slowing down in SH patients compared with healthy controls. Patients will be observed further in order to monitor the effects of thyroxine treatment.

        Key words: event-related potentials, subclinical hypothyroidism, cognitive dysfunction, P3, thyroxine