Effects of startle and laughter in cataplectic subjects: a neurophysiological study between attacks.

OBJECTIVES: Cataplexy, when unequivocally present together with excessive daytime sleepiness, is diagnostic for narcolepsy. Unfortunately, it is difficult to induce cataplexy during consultation. In this study we tried to assess presumed subclinical expressions of cataplexy using neurophysiological tests. METHODS: In this controlled explorative study, we studied 14 patients with a clear history of cataplexy and 12 matched controls using standard H-reflex, H/M ratios, audiospinal reflex, H-reflexes modulated by emotions and startle reflexes. RESULTS: H-reflexes were attenuated during laughter in patients as well as controls. Startle reflexes were increased in patients. Audiospinal reflexes were not influenced. CONCLUSIONS: The patterns found add relevant knowledge concerning pathophysiological mechanisms and involved brain areas in cataplexy, and may reflect subclinical expressions of cataplexy. The presumed specificity of the abolishment of H-reflexes during cataplectic attacks is questioned by our findings. The exaggerated startle reflex is in line with recent findings concerning involved brain areas in narcolepsy.