Question
Subcutaneous mycosis
Answer
Subcutaneous mycoses are fungal infections involving the dermis, subcutaneous tissue, and sometimes underlying muscle/bone, typically acquired via traumatic inoculation (e.g., a thorn prick, splinter) of an organism normally found in soil/plant material — distinct from superficial mycoses (confined to outer skin/hair/nails) and systemic mycoses (acquired by inhalation, causing internal organ disease).
Important examples:
- Sporothrix schenckii — causes sporotrichosis (“rose gardener’s disease”); dimorphic fungus; classically produces a lymphocutaneous pattern — a primary nodule at the inoculation site with a chain of secondary nodules along lymphatic drainage; diagnosed by culture showing thermal dimorphism (mould at 25°C, cigar-shaped yeast at 37°C); treated with itraconazole or saturated potassium iodide solution.
- Madurella mycetomatis (and related fungi) — causes eumycetoma (Madura foot); presents with tumefaction, multiple sinus tracts, and characteristic black grains; diagnosed by demonstrating broad, septate hyphae in grains; treated with prolonged itraconazole ± surgery.
- Basidiobolus ranarum — causes subcutaneous zygomycosis (basidiobolomycosis); a firm, slowly enlarging subcutaneous swelling, typically on limbs of children in tropical regions.
- Chromoblastomycosis agents (Fonsecaea pedrosoi, Cladophialophora carrionii) — cause chronic, verrucous/cauliflower-like skin lesions; histologically characterized by pathognomonic copper-coloured sclerotic (Medlar) bodies.
- Rhinosporidium seeberi — causes rhinosporidiosis (nasal mucosal polypoid mass); now classified as an aquatic protistan parasite rather than a true fungus, but traditionally grouped here.
Common features: slow, chronic, localized progression; generally do not disseminate systemically (unlike systemic mycoses); require traumatic inoculation for entry (unlike superficial dermatophyte spread by direct contact, or systemic mycoses acquired by inhalation); diagnosis relies on a combination of clinical appearance, direct microscopy of exudate/tissue, culture, and histopathology; treatment typically combines prolonged antifungal therapy with surgical intervention where feasible.