Chlorpyrifos-induced delayed myelopathy and pure motor neuropathy: a case report

Organophosphate (OP) poisoning is known to cause delayed neurological manifestations. Chlorpyrifos, an OP, causes a delayed syndrome that is characterized by a motor sensory polyneuropathy. Pure motor neuropathy with intact sensory conduction is rarely documented. Rapidly evolving delayed myelopathy is extremely uncommon.

A healthy 15-year-old female was admitted to hospital with cholinergic crisis due to ingestion of a large dose of chlorpyrifos (OP). She was treated with atropine and recovered completely without any neurological symptoms or signs. She came to hospital 6 weeks later with upper and lower motor neuron signs involving the lower limbs without sensory loss. By the end of 7 weeks, there was urinary incontinence. At 2-month follow-up, she had progressive spasticity. Electrophysiological studies revealed a pure motor neuropathy. Spine magnetic resonance imaging showed early signs of thoracic cord atrophy. Other causes of myelopathy were excluded.

Chronic neurotoxicity due to OP poisoning is dependent on several factors: chemical composition of the OP, dose systematized, and the administration of anitcholinergics for cholinergic crisis. The pathology of OP-induced delayed neuropathy involves a central-peripheral distal axonopathy. Peripheral distal axonopathy results in a predominantly motor polyneuropathy. Axonopathy of the central nervous system results in myelopathic features that makes for a poorer prognosis.