A 9-year-old unvaccinated child recovers from membranous pharyngitis. Three weeks later he develops nasal regurgitation of fluids and a nasal voice, followed by weakness of extraocular muscles and then a distal symmetrical sensorimotor neuropathy. This sequence of neurological complications is best explained by:
- A Local action of the toxin on cranial nerves followed by demyelination of peripheral nerves ✓
- B Haematogenous spread of the organism to the central nervous system
- C Immune complex deposition in the vasa nervorum
- D Antibody cross-reactivity between bacterial M protein and myelin
Correct answer: A. Local action of the toxin on cranial nerves followed by demyelination of peripheral nerves
Explanation
Diphtheritic polyneuropathy follows a characteristic descending then ascending pattern: palatal and pharyngeal palsy first from local toxin action, then oculomotor and ciliary involvement, and finally a delayed distal polyneuropathy around the third to fifth week. The toxin damages Schwann cells and myelin directly. Cross-reactive anti-M protein antibodies belong to rheumatic fever, and immune complex vasculitis does not produce this ordered sequence.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.