Actinomycetoma — DTM&H MCQ

Correct answer: C — Actinomycetoma

Actinomycetoma (option C) is correct because the combination of a chronic swollen foot (Madura foot) with multiple draining sinuses, pale (as opposed to black) grains, and filamentous bacteria on microscopy is classic for actinomycetoma, caused by aerobic actinomycetes such as Nocardia, Actinomadura and Streptomyces species. The key discriminator is the organism seen on microscopy: fine, thin, branching bacterial filaments within the grain, distinguishing this from the broader, septate fungal hyphae of eumycetoma. Geographic and occupational context (a farmer with traumatic soil inoculation in an endemic tropical/subtropical belt including Mexico) further supports mycetoma over the other differentials. This distinction matters clinically because actinomycetoma responds well to prolonged combination antibacterial therapy, whereas eumycetoma usually requires surgery plus antifungals with poorer cure rates. Why the other options are wrong: A. Sporotrichosis: caused by Sporothrix schenckii, typically presents as lymphocutaneous nodules or ulcers along lymphatic channels, not a mass with grain-discharging sinuses, and grains are not a feature. B. Tungiasis: this is infestation by the sand flea Tunga penetrans causing a painful papule with a central black punctum, not a chronic swollen mass with sinuses or grains, and no filamentous organisms are seen. D. Eumycetoma: caused by fungi (e.g. Madurella mycetomatis) producing broad septate hyphae, not bacterial filaments, and grains are classically black/dark rather than pale. E. Madura leishmaniasis: not a recognised clinical entity; cutaneous/mucocutaneous leishmaniasis causes ulcerating skin lesions without grains or sinus tracts, and amastigotes, not filamentous organisms, are seen. Key point: pale grains with fine branching bacterial filaments on microscopy indicate actinomycetoma, treatable with prolonged antibiotics, whereas dark grains with broad fungal hyphae indicate eumycetoma, which needs surgery plus antifungals.

Reference: CDC Fungal Diseases, Mycetoma: Information for Health Professionals (grain morphology and treatment differences between actinomycetoma and eumycetoma), https://archive.cdc.gov/www_cdc_gov/fungal/diseases/mycetoma/health-professionals.html