We report the case of a 58-year-old male who presented with 2-day history of gait unsteadiness and paresthesias. His medical history was notable for a recent upper respiratory tract infection and accidental exposure to organophosphate (OP) insecticide. His exam was significant for stocking-glove distribution paresthesias, horizontal diplopia, muscle weakness in the proximal upper and lower extremities, wide-based gait and absent deep tendon reflexes, initially suggestive of Guillain-Barré Syndrome (GBS). He was empirically treated with intravenous immunoglobulin (IVIG). However, lumbar puncture did not show albuminocytologic dissociation and the patient’s condition worsened, with increasing muscle weakness and secretion burden, concerning for progressive respiratory failure. Given the temporal relation to pesticide exposure and nerve conduction studies showing features of neuromuscular junction failure rather than an axonal or demyelinating motor polyneuropathy, a diagnosis of Intermediate Syndrome (IMS). Low cholinesterase RBC and normal cholinesterase plasma further supported this diagnosis. The patient was managed with close respiratory monitoring and supportive care and was eventually discharged to acute rehabilitation.

This case highlights the diagnostic challenge of IMS mimicking GBS and emphasizes the need for thorough clinical history even in patients without any occupational risk factors presenting with acute flaccid paralysis.