Lesch-Nyhan syndrome with delayed onset of self-mutilation: hyperactivity of interneurons at the brainstem and blink reflex.

We studied a case of Lesch-Nyhan syndrome with delayed onset of self-mutilation. Athetotic cerebral palsy and mental retardation were diagnosed at 1 year old, but the disease was not suspected until age 8 years when he began biting his lips and fingers. There was no obvious alteration of catecholamine in urine and CSF. We attempted to induce a series of blink reflexes by electric, mechanical and photic procedures. The R1 amplitude increased and the latency of the R2 shortened compared with controls. This shows that not only orbicularis motoneuron itself, but also uncrossed interneurons, are in a state of hyperexcitability. The contralateral R2 was poor which was in favour of hypoexcitability of the crossed interneurons at the brainstem. The significant large response was obtained by photic procedure which was in favour of hyperexcitability of the motoneurons. Therefore, it is demonstrated that a thorough examination of blink reflexes provides a useful method for examination of a state of the underlying neural activity.