The natural history of chronic peripheral polyneuropathy following lifetime low-level organophosphate (OP) exposure was investigated. A pilot study (1984-1987) conducted in rural communities in Israel detected subtle reversible in-season changes in nerve conduction patterns of 17 field workers out of 214 residents exposed to seasonal drift containing OP's. We examined 60 individuals (males: 50/60; 83.3%) from the original cohort still residing (more than 40 years) in the same communities. Exposure assessment was based on reports by Israeli institutions and the Bureau of Statistics. Information on personal status, work experience, exposures and symptoms was collected by questionnaires. The nervous system was systematically studied, evaluating cortical upper motor neurons, corticospinal tracts, lower motor neurons and peripheral nerves. Electrophysiological studies included conduction velocities, amplitudes and distal latencies of sensory and motor median, ulnar, tibial and sural nerves; F-waves for proximal nerve functions; thermal and pain thresholds for small thinly-myelinated and non-myelinated fibers; transcranial magnetic stimulation for large fibers. Clinical and electrophysiological features of Carpal Tunnel Syndrome were found in 18% of the subjects, atypically in males only. Fingertips' tingling correlated with both axonal and myelin-dependent parameters (lower wave amplitudes and prolonged latency periods, respectively) in the sensory median nerves bilaterally. OP exposure significantly correlated to prolonged distal latency in the right median sensory nerve (r=0.29; p=0.052; n=45) and lower wave amplitude in the right sural nerve (p=0.031). These findings attest to subtle, predominantly sensory peripheral polyneuropathy following lifetime low-level exposures to drifts containing OP.
Keywords: Carpal Tunnel Syndrome; Long term low level exposure; Organophosphate; Peripheral neuropathy; Pesticide.
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