In mass casualty organophosphorus compound (OPC) poisoning, intermediate syndrome (IMS) is a clinical entity distinct from acute cholinergic crisis. The CORRECT statement about IMS is:

• A IMS occurs within 30 minutes of acute OPC ingestion and is caused by nicotinic receptor hyperstimulation
• B IMS is caused by delayed reactivation of cholinesterase and responds well to further atropine doses
• C IMS is a OPIDN (organophosphate-induced delayed polyneuropathy) involving peripheral demyelination
• D IMS occurs 24–96 hours after apparent resolution of acute cholinergic crisis, involves proximal limb weakness, neck flexor weakness, and respiratory muscle paralysis due to acetylcholine accumulation at nicotinic neuromuscular junctions ✓

Explanation

Intermediate syndrome occurs 24–96 hours (1–4 days) after an acute OPC crisis that appeared resolved, causing proximal limb weakness, neck flexion weakness, and respiratory paralysis, potentially causing delayed death. It results from persistent acetylcholine excess at nicotinic neuromuscular junctions causing receptor desensitisation and dysfunction. It does not respond to atropine (which is muscarinic antagonist) and is treated supportively with mechanical ventilation. OPIDN is a distinct third syndrome occurring weeks later causing peripheral demyelinating neuropathy.

Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.

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Written and medically reviewed by the StethoPrep medical team.