Cassava cyanide toxicity — DTM&H MCQ

Correct answer: A — Konzo

The correct answer is A, Konzo. Konzo is an abrupt onset, non-progressive, symmetric spastic paraparesis caused by chronic dietary exposure to cyanogenic glycosides from insufficiently processed bitter cassava, typically during drought or famine when protein intake falls and reliance on cassava rises. The diagnosis is clinical, based on WHO criteria: onset within one week in a previously healthy child, symmetric spastic gait abnormality, and exaggerated knee or ankle reflexes without spinal disease. Crucially there is no sensory or autonomic involvement, which fits the stem exactly, and outbreaks cluster in whole communities under nutritional stress, exactly as described. Why the other options are wrong: D. Poliomyelitis: causes an acute flaccid, asymmetric paralysis with reduced or absent reflexes, not spasticity, and is due to enterovirus infection, not diet. B. Beriberi: thiamine deficiency causes a peripheral neuropathy or high output cardiac failure with sensory loss and diminished reflexes, not isolated upper motor neuron spastic paraparesis. C. Lathyrism: also produces acute spastic paraparesis but follows consumption of Lathyrus sativus (grass pea), and in Africa is essentially confined to Ethiopia, not cassava-dependent drought regions. E. Guillain-Barré syndrome: presents with ascending flaccid weakness, areflexia, and often sensory symptoms, evolving over days to weeks, not the abrupt symmetric spasticity described here. Key point: Acute, non-progressive, symmetric spastic paraparesis without sensory loss in a community over-relying on poorly processed bitter cassava during drought is konzo, distinguishing it from lathyrism (grass pea), poliomyelitis (flaccid, asymmetric) and GBS (ascending flaccid, sensory).

Reference: WHO diagnostic criteria for konzo, cited in: Konzo, a distinct neurological disease associated with food (cassava) cyanogenic poisoning, PMC (Nunga Musio Mwanga et al.), and summarised on Wikipedia: Konzo (WHO criteria: symmetric spastic gait abnormality, onset under one week with subsequent non-progressive course, exaggerated knee/ankle jerks without spinal disease). https://en.wikipedia.org/wiki/Konzo