The palmo-mental reflex in vibroacoustic disease.
BACKGROUND
Vibroacoustic disease (VAD), is a multisystemic nosological entity, caused by occupational exposure to large pressure amplitude (> or = 90 dB SPL) and low frequency (< or = 500 Hz) (LPALF) noise. The most common neurological finding in patients with VAD is the palmomental reflex (PMR). The aim of this study is to evaluate the frequency and characteristics of this primitive reflex in a population of VAD patients.


METHODS
Sixty individuals, occupationally exposed to LPALF noise underwent a neurological examination. In each one, unilateral contraction of the chin muscles was triggered through the stimulation of the thenar eminence. When a response habituation was observed, or when there was no response except previously existing skin retraction and small dimples, an EMG was performed. All these subjects also received brain MRI and measurement of endogenous evoked potentials.


RESULTS
Thirty individuals presented unilateral or bilateral PMR; 26 of these presented changes in the brain MRI. EMG measurement evidenced continuous contraction of the chin muscles, without visible PMR, triggered by the stimulation of the thenar eminence.


CONCLUSIONS
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 structures.
Martinho Pimenta
A J
AJ
Santo António dos Capuchos Hospital, Lisbon, Portugal.
Castelo Branco
M S
MS
Castelo Branco
N A
NA
D000328:Adult; D000401:Aircraft; D002493:Central Nervous System Diseases / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology*; D002680:Chin; D004576:Electromyography; D005071:Evoked Potentials; D005152:Facial Muscles / Q000503:physiopathology*; D006185:Habituation, Psychophysiologic; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009069:Movement Disorders / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology*; D009460:Neurologic Examination; D009622:Noise / Q000009:adverse effects*; D009784:Occupational Diseases / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology*; D012021:Reflex, Abnormal; D013933:Thumb; D014732:Vibration / Q000009:adverse effects*