Lathyrism — DTM&H MCQ
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Correct answer: B — Lathyrism
Lathyrism (option C) is correct because the stem describes prolonged, near-exclusive dietary reliance on grass pea (Lathyrus sativus) in a famine setting, which is the specific exposure that causes this toxico-nutritional myelopathy. The disease is caused by the neuroexcitatory toxin BOAA/beta-ODAP acting at glutamate (AMPA) receptors, producing selective damage to the corticospinal tracts (Betz cells) and resulting in an irreversible, non-progressive, symmetrical spastic paraparesis in young adults, with sparing of sensation, sphincters and cognition. Grass pea is a classic drought-resistant famine food, so an outbreak in a village dependent on it for months, with young men predominantly affected, is textbook lathyrism. Diagnosis is clinical, based on dietary history and exclusion of other myelopathies, since there is no confirmatory laboratory test. Why the other options are wrong: C. Konzo: also causes acute symmetrical spastic paraparesis but follows insufficiently processed bitter cassava (cyanogenic glycoside) consumption, not grass pea; the staple food in the stem is diagnostic for lathyrism, not konzo. D. Vitamin B12 deficiency: causes subacute combined degeneration with dorsal column sensory loss, peripheral neuropathy and cognitive change, not a pure symmetrical spastic paraparesis linked to a specific legume. A. Tropical spastic paraparesis: caused by HTLV-1 infection, has a slowly progressive course with sensory and sphincter involvement, and is unrelated to grass pea ingestion. E. Poliomyelitis: causes an asymmetrical flaccid (lower motor neurone) paralysis with areflexia, the opposite pattern to the symmetrical upper motor neurone spasticity described here. Key point: A famine population with prolonged grass pea consumption developing irreversible symmetrical spastic paraparesis (sparing sensation and sphincters) is lathyrism, distinguished from konzo by the causative staple (grass pea versus cassava).
Reference: Manson's Tropical Diseases (23rd edition), chapter on Nutritional and Metabolic Disorders / Neurolathyrism, and PMC review 'Konzo: a nutrition-related tropical spastic paraparesis' (2024) summarising differential diagnosis of nutrition-related spastic paraparesis, https://pmc.ncbi.nlm.nih.gov/articles/PMC13110498/