Blink reflex in hyperthyroidism.

Although there are studies regarding the effects of thyroid hormones on some neurologic reflexes, literature lacks knowledge of the effects of thyroid hormones on blink reflex circuits. To understand the behaviour of excess thyroid hormone on this circuit that involves synapses in brainstem, we studied electrically elicited blink reflexes of 7 patients with hyperthyroidism, 8 patients with hyperthyroidism who were under therapy and 14 volunteers as control by electroneuromyograph. Mean values of the latencies and amplitudes of the R1 and R2 responses were not statistically different between groups, while the duration of R2 response and controlateral R2 response were found shorter in patients with hyperthyroidism comparing to the patients under therapy and controls. We have thought that these findings might reflect the inhibitor effect of the excess thyroid hormone on polysynaptic reflex arc of the blink response.