In organophosphate poisoning, intermediate syndrome (IMS) differs from acute cholinergic crisis in that IMS occurs 24–96 hours after poisoning and involves weakness of which specific muscle groups?

• A Smooth muscle of the bowel and bladder causing paralytic ileus
• B Cardiac muscle causing myocarditis and arrhythmias only
• C Distal small muscles of the hands and feet with foot drop
• D Proximal limb muscles, neck flexors, and cranial nerve-innervated muscles (facial, extraocular) with respiratory muscle weakness ✓

Explanation

Intermediate syndrome (IMS), first described by Senanayake and Karalliedde (1987), occurs 24–96 hours after resolution of the acute cholinergic phase. It is characterised by selective weakness of: proximal limb muscles (difficulty rising from sitting), neck flexors, muscles innervated by cranial nerves (facial weakness, extraocular palsies), and intercostal/respiratory muscles. It is thought to result from a sustained nicotinic receptor desensitisation or a post-synaptic NMJ defect at nicotinic receptors due to persistent AChE inhibition. Respiratory failure in IMS is the main cause of death.

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

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