Subcutaneous cysticercosis — DTM&H MCQ

Correct answer: C — Subcutaneous cysticercosis

The correct answer is C, subcutaneous cysticercosis. The biopsy finding of a calcified cystic structure containing a scolex is pathognomonic for a Taenia solium larval cyst, and subcutaneous nodules are a recognised extra-neural site for cysticerci in endemic regions of Southeast Asia including Laos. Infection occurs after ingestion of T. solium eggs (faecal-oral, contaminated food or water, or autoinfection), not from paddy water exposure itself, but paddy farming reflects the poor sanitation and free-range pig husbandry that sustain the parasite's lifecycle in this region. Histologically the larva (cysticercus) has a bladder wall and an invaginated scolex with hooklets, which calcifies over time, exactly matching the description given. Why the other options are wrong: D. Onchocercomata: these are subcutaneous nodules caused by adult Onchocerca volvulus, found in Africa and parts of Latin America, not Southeast Asia, and contain coiled adult worms rather than a cystic structure with a scolex. E. Cutaneous larva migrans: this produces a serpiginous, migratory, intensely itchy track from hookworm larvae penetrating skin, not a discrete calcified nodule, and there is no cyst or scolex on histology. B. Hydatid cyst: caused by Echinococcus granulosus, typically affecting liver or lung with a laminated germinal layer and protoscoleces, but primary isolated subcutaneous hydatid disease is rare and the epidemiological link here (rice paddies, pigs) fits T. solium rather than a dog-sheep cycle. A. Dracunculiasis: caused by Dracunculus medinensis, presents with a painful blistering lesion from which an adult female worm emerges, typically on the lower limb after drinking contaminated water, not a painless calcified cyst, and it is now essentially eradicated. Key point: a painless subcutaneous nodule with a calcified cyst and visible scolex on histology is diagnostic of Taenia solium cysticercosis, and any patient with this finding should be screened for concurrent neurocysticercosis.

Reference: Garcia HH, Gonzalez AE, Gilman RH. Taenia solium cysticercosis. PMC (NIH) review article: https://pmc.ncbi.nlm.nih.gov/articles/PMC3103219/