The palmo-mental reflex in vibroacoustic disease

Background: Vibroacoustic disease (VAD), is a multisystemic nosological ent ity, caused by occupational exposure to large pressure amplitude (greater t han or equal to 90 dB SPL) and low frequency (less than or equal to 500 Hz) (LPALF) noise. The most common neurological finding in patients with VAD i s the palmomental reflex (PMR). The aim of this study is to evaluate the fr equency and characteristics of this primitive reflex in a population of VAD patients. Methods: Sixty individuals, occupationally exposed to LPALF nois e underwent a neurological examination. In each one, unilateral contraction of the chin muscles was triggered through the stimulation of the thenar em inence. When a response habituation was observed, or when there was no resp onse except previously existing skin retraction and small dimples, an EMC w as performed. All these subjects also received brain MRI and measurement of endogenous evoked potentials. Results: Thirty individuals presented unilat eral or bilateral PMR; 26 of these presented changes in the brain MRI. EMC measurement evidenced continuous contraction of the chin muscles, without v isible PMR, triggered by the stimulation of the thenar eminence. Conclusion : PMR is present in 50% of the patients with VAD. In the VAD patients, the frequency of abnormal chin muscle activity is higher than the frequency of PMR and represents a loss of the cortical control over the brainstem struct ures.