Neurological aspects of vibroacoustic disease.

INTRODUCTION: Mood and behavioral abnormalities are the most common early findings related to vibroacoustic disease (VAD). Other signs and symptoms have been observed in VAD patients. Brain MRI discloses small multifocal lesions in about 50% of subjects with more than 10 yr of occupational exposure to large pressure amplitude (> or = 90 dB SPL) and low frequency (< or = 500 Hz) (LPALF) noise. However, to date, there have been no studies globally integrating all the neurological, imaging and neurophysiological data of VAD patients. This is the main goal of this study. METHODS: The 60 male Caucasians diagnosed with VAD were neurologically evaluated in extreme detail in order to systematically identify the most common and significant neurological disturbances in VAD. RESULTS: This population demonstrates cognitive changes (identified through psychological and neurophysiological studies (ERP P300)), vertigo and auditory changes, visual impairment, epilepsy, and cerebrovascular diseases. Neurological examination reveals pathological signs and reflexes, most commonly the palmo-mental reflex. CONCLUSIONS: A vascular pattern underlying the multifocal hyperintensities in T2 MR imaging, with predominant involvement of the small arteries of the white matter, is probably the visible organic substratum of the neurological picture. However, other pathophyisological mechanisms are involved in epileptic symptomatology.

Balance disturbances in individuals with vibroacoustic disease.

INTRODUCTION: In previous studies, patients with vibroacoustic disease (VAD) presented hyperintense foci in T2 of the cerebral white matter, brainstem and basal nuclei. The most probable etiology is ischemia. One of the most frequent complaints of these patients is balance disturbances which, in two cases, has threatened the patients' ability to maintain their jobs. The purpose of this study was to compare two methods, one neurophysiological (auditory evoked potentials - AEP) and the other structural imaging (brain MRI), in order to determine to what extent the changes detected with these methods may be related to each other in this pathology. METHODS: Twenty individuals occupationally exposed to large pressure amplitude (> or = 90 dB SPL) and low frequency (< or = 500 Hz) noise, received neurological and otorhinolaryngological examinations. All of them had previously received audiograms, tympanograms and electronystagmograms. All 20 patients also received brain MRI and AEP studies. RESULTS: The individuals with vertigo and changes of the AEP present the greater number of changes in the brain MRI. CONCLUSION: This could be an indication that in many VAD cases vertigo may have a central origin.

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. 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 structures.

Effects of occupational exposure to low frequency noise on cognition.

INTRODUCTION: Previous studies performed on groups of workers employed in the aeronautical industry revealed morphological vascular changes of the central nervous system (CNS) and some difficulty in attention and memory retention. The goal of this study is, therefore, to determine whether prolonged occupational exposure to large pressure amplitude (> or = 90 dB SPL) and low frequency (< or = 500 Hz) (LPALF) noise leads to cognitive deterioration. METHODS: We observed 40 male workers employed as aircraft technicians, with average age of 43.3 yr (range 35-56, SD = 4.82) occupationally exposed to LPALF noise for a long period of time, average 22 yr (range 13-30, SD = 4.90), and 30 educationally- and age-matched male controls. None of the subjects had a history of alcoholism, and all were drug-free. The P300 event-related brain potential elicited with an auditory discrimination task was recorded and psychological tests (the Wechsler memory scale and the Toulouse-Piéron test) were performed. RESULTS: The P300 latency was significantly longer (328.5 vs. 307.5 ms, F = 11.7, deg. signif.=0.001) and the amplitude significantly smaller (10.9 vs. 12.6, F = 4.3, deg. signif.=0.04) in the exposed group than in the controls. No significant differences were found in the results of the Toulouse-Piéron test. The different subscales of the Wechsler memory scale did not show any significant difference except in the immediate verbal memory, where the exposed workers were found to have poorer results than the controls (10.0 vs. 11.3, F = 5.6, deg. signif.=0.02). However, the memory quotient obtained from the Wechsler memory scale indicated a significant difference between both groups (101.8 vs. 108.3, F = 10.1, deg. signif.=0.002); exposed subjects presented lower results. CONCLUSION: These findings suggest that prolonged exposure to LPALF noise might contribute to cognitive impairment and that the P300 event-related brain potential recording may be a valuable diagnostic tool.

Facial dyskinesia induced by auditory stimulation: a report of four cases.

INTRODUCTION: The Vibroacoustic Disease (VAD) is an occupational pathology induced by long-term (>10 yr) exposure to large pressure amplitude (> or = 90 dB SPL) and low frequency (< or = 500 Hz) noise. During studies contributing to the characterization of VAD, abnormal facial movements induced by repetitive auditory stimuli were observed in one individual employed as an aeronautical mechanic. The goal of this study was to investigate the existence of movement disorders triggered by auditory stimuli in a group of VAD-diagnosed patients. METHODS: Sixty VAD patients received auditory and median nerve stimulation. Simultaneously, EEG monitoring was performed. RESULTS: Abnormal myoclonus movements were triggered by auditory stimuli in four patients. EEG recordings were normal in all 60 patients. Stimulation of the median nerves did not trigger any abnormal movements. CONCLUSION: These data suggest that this facial dyskinesia has a subcortical origin.

ERP P300 and brain magnetic resonance imaging in patients with vibroacoustic disease.

INTRODUCTION: Subjects occupationally exposed to large pressure amplitude (> or = 90 dB SPL) and low frequency (< or = 500 Hz) (LPALF) noise for long term periods (>10 yr) can develop vibroacoustic disease (VAD). One of the earliest complaints of VAD patients deals with memory and attention disturbances. On the other hand, in over 50% of these patients, magnetic resonance imaging (MRI) of the CNS revealed cortical atrophy and dilation of the perivascular spaces, and small hyperintense lesions in T2 of the cerebral white matter, basal ganglia, and brainstem. The purpose of this study is to investigate whether there is any relationship between these morphological changes and the event-related potentials (ERP) P300 parameters. METHODS: Sixty aeronautical workers with more than 10 yr of LPALF noise exposure were studied using brain MRI and ERP P300. A careful neurological examination had been previously performed on all of them. RESULTS: The neurological examination revealed abnormalities in 80%, the most common finding being the archaic palmo-mental reflex. Some 37 subjects had hyperintense foci in T2 of the subcortical and periventricular white matter, the basal ganglia and the brainstem. Comparing the ERP P300 amplitude and latency values, morphology and topography, obtained in these 37 subjects with the data from the 23 who did not have any morphological changes in CNS, we found a strong correlation between the brain MRI lesions and the neurophysiological changes (p < 0.01). CONCLUSIONS: These results are important for understanding the pathophysiology of the cognitive impairment found in VAD patients.

Epilepsy in the vibroacoustic disease: a case report.

INTRODUCTION: Late-onset epilepsy was one of the first neurological problems identified in patients diagnosed with vibroacoustic disease. Other clinical situations, such as automatisms and rage-like reaction crises were also observed. Some cases of epileptic seizures were triggered by different types of stimuli. CASE REPORT: This study describes the clinical case of a 30-yr-old male metal-worker who had epileptic seizures when he used vibratory tools common to his profession, such as drills and sanders. We performed a 21-channel EEG during a seizure induced in the laboratory by direct contact of a vibratory tool with his right hand. This allowed us to view the electrical discharge of his left hemisphere. The entire procedure was simultaneously videotaped while a partial motor crisis was observed. Brain MRI of this subject revealed multiple hyperintense focal lesions in the sub-cortical white matter. Echocardiography revealed thickening of the pericardium and valve structures. COMMENTARY: To the authors' knowledge, this is the first documented case of reflex epilepsy due to vibratory stimuli. We briefly discuss the possible pathophysiological mechanisms of this clinical event.