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Describe the subcutaneous mycoses with their features and diagnosis.

Microbiology · 2nd Professional — Para-Clinical

Definition and Common Features

Subcutaneous mycoses are chronic infections of the dermis, subcutaneous tissue and sometimes bone, caused by fungi of low virtue that live in soil and vegetation and are introduced by traumatic implantation.

Common features — a history of minor penetrating injury, often forgotten; an indolent chronic course over months to years; localised disease with little tendency to disseminate in the immunocompetent; and a marked occupational association with barefoot agricultural work
They occur in immunocompetent people, unlike the opportunistic mycoses, and are diseases of exposure rather than of immunity

Disease	Organism	Features
Mycetoma (Madura foot)	Eumycetoma — fungi (Madurella); actinomycetoma — bacteria (Nocardia, Actinomadura, Streptomyces)	The triad of painless swelling, multiple discharging sinuses, and grains in the discharge; destroys underlying bone. Named after madurai. Distinguishing the fungal from the bacterial form is essential, because actinomycetoma responds to antibiotics while eumycetoma needs antifungals and usually surgery
Sporotrichosis	Sporothrix schenckii — a dimorphic fungus	The "rose gardener disease" — implanted by a thorn, splinter or sphagnum moss. A nodule at the site ulcerates, then further nodules appear in a linear chain along the lymphatics — the characteristic lymphocutaneous pattern. Cigar-shaped yeasts and asteroid bodies in tissue. Treated with itraconazole, or the traditional saturated potassium iodide
Chromoblastomycosis	Pigmented (dematiaceous) fungi — Fonsecaea, Cladophialophora	Slowly progressive warty, cauliflower-like verrucous plaques on the leg or foot. Diagnostic finding: sclerotic (muriform or "copper penny") bodies — thick-walled brown septate cells in tissue. Notoriously difficult to treat; itraconazole with terbinafine, cryotherapy, surgery
Phaeohyphomycosis	Dematiaceous fungi	Cysts and abscesses containing dark-walled hyphae, distinguishing it from chromoblastomycosis, in which the fungus is present as sclerotic bodies
Rhinosporidiosis	Rhinosporidium seeberi — now classified among the Mesomycetozoea, not a true fungus, and it cannot be cultured	Friable, vascular, polypoid masses in the nose and conjunctiva that bleed readily. Associated with bathing in stagnant ponds. Endemic in southern India and Sri Lanka. Treated by surgical excision with cautery of the base; recurrence is common and drugs are ineffective
Lobomycosis, subcutaneous zygomycosis	Lacazia; Basidiobolus, Conidiobolus	Basidiobolomycosis causes a firm painless subcutaneous swelling in children in tropical India

CLINICAL PEARL

The grain in a mycetoma sinus tells you whether the patient keeps the limb. An actinomycetoma is caused by bacteria and responds to co-trimoxazole with amikacin or dapsone, often completely. A eumycetoma is fungal, responds poorly to antifungals, and frequently ends in amputation. The grains differ in colour and in their microscopic appearance — thin bacterial filaments against broad fungal hyphae — and the examination costs nothing.

Diagnosis and Applied Aspects

Examine the discharge for grains macroscopically, then crush and stain them; Gram stain shows the fine branching filaments of actinomycetoma and KOH shows the broad hyphae of eumycetoma
Biopsy with special stains — PAS and methenamine silver; look specifically for sclerotic bodies (chromoblastomycosis), asteroid bodies (sporotrichosis) and sporangia (rhinosporidiosis)
Culture on Sabouraud agar at 25 and 37°C, which is slow; imaging to assess bone involvement in mycetoma
Footwear is the single most effective preventive measure for mycetoma and chromoblastomycosis, and remains under-emphasised in the endemic belts of India
Ask about the occupation and about minor trauma; the injury may have occurred months or years earlier and will not be volunteered
Consider lymphocutaneous spread in a chain of nodules — the differential includes sporotrichosis, Mycobacterium marinum, nocardiosis and leishmaniasis, and the history of exposure separates them
Footwear prevents mycetoma, and this is a simple, cheap and under-emphasised public health measure in the endemic districts of India
These infections are chronic and painless, so patients present late, often after bone destruction has occurred; a high index of suspicion in an agricultural worker with a slowly enlarging swelling shortens that delay
Mycetoma is now recognised by the WHO as a neglected tropical disease, and India lies within the endemic "mycetoma belt"
Treatment is prolonged — months to years — and adherence is the principal determinant of outcome; patients frequently stop when the discharge settles and relapse follows
Rhinosporidiosis recurs after excision unless the base is thoroughly cauterised, and no drug is reliably effective, so surgical technique determines the result
Do not mistake a verrucous plaque for tuberculosis verrucosa cutis or squamous carcinoma; a scraping or biopsy showing sclerotic bodies settles it immediately
Immunosuppression changes the picture — sporotrichosis may disseminate rather than remaining lymphocutaneous, and requires systemic amphotericin B rather than itraconazole

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