On the origin of sensory impairment and altered pain perception in Prader-Willi syndrome: a neurophysiological study

INTRODUCTION: High pain threshold is a supportive diagnosis criterion for Prader-Willi syndrome (PWS), but its pathogenesis is poorly understood. In this study we investigate sensory pathways in PWS, in order to evaluate peripheral or central involvement in altered sensory perception. METHODS: 14 adult PWS patients, 10 obese non-diabetic people and 10 age-matched controls underwent: (a) motor/sensory nerve conduction velocities at the upper and lower limbs; (b) palmar/plantar sympathetic skin response; (c) somatosensory evoked potentials from upper/lower limbs; (d) quantitative sensory testing to measure sensory threshold for vibration, warm and cold sensation, heat and cold-induced pain and (e) blood sample analysis to evaluate glucose and insulin levels and to calculate the quantitative insulin-sensitivity check index (QUICKI). RESULTS: Electroneurographic examination, sympathetic skin response and somatosensory evoked potentials were all within normal ranges. In the PWS group, thermal and pain thresholds but not vibratory were significantly higher than in healthy and obese people (p<0.05). Sensory threshold did not correlate with BMI nor with QUICKI. CONCLUSIONS: Our data suggest that altered perception in PWS does not seem attributable to a peripheral nerve derangement due to metabolic factors or obesity. Impairment of the small nociceptive neurons of dorsal root ganglia or involvement of hypothalamic region may not be excluded.