Subcutaneous Mycoses

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Introduction - Deep Skin Invaders

  • Fungi invade dermis, subcutaneous tissue, muscle, fascia.
  • Chronic, localized infections.
  • Caused by diverse, saprophytic fungi.
  • Portal of entry: Skin trauma (thorns, splinters).
  • Organisms reside in soil, decaying vegetation.
  • Infections often indolent, slowly progressive.
  • Host immunity plays a key role in disease manifestation.

⭐ Subcutaneous mycoses typically result from traumatic inoculation of fungi from soil or vegetation into deeper skin layers.

  • Common in tropical/subtropical regions, agricultural workers.
  • Diagnosis: Microscopy, culture, histopathology, molecular tests (PCR).

Sporotrichosis - Rose Gardener's Revenge

  • Agent: Sporothrix schenckii (thermally dimorphic fungus).
  • Transmission: Traumatic inoculation from soil, sphagnum moss, rose thorns.
  • Clinical Forms:
    • Lymphocutaneous (most common): Initial papule → ulcerates. Nodules ascend along lymphatics ("sporotrichoid spread").
    • Fixed cutaneous: Solitary chronic plaque/ulcer.
    • Disseminated: Rare; in immunocompromised (joints, lungs).
  • Diagnosis:
    • Culture (gold standard): Tissue/pus. Yeast at 37°C, mold at 25°C.
    • Biopsy: Granulomatous inflammation; cigar-shaped yeast cells.

    ⭐ The presence of asteroid bodies (Splendore-Hoeppli phenomenon) surrounding yeast cells is characteristic but not pathognomonic for sporotrichosis.

  • Treatment:
    • Itraconazole (DOC for cutaneous/lymphocutaneous).
    • SSKI (Saturated Solution of Potassium Iodide).
    • Amphotericin B (severe/disseminated). Sporotrichosis lymphocutaneous lesions

Chromo & Phaeo - Dark Fungi Drama

  • Caused by dematiaceous (dark-walled/pigmented) fungi.
  • Chromoblastomycosis:
    • Etiology: Fonsecaea pedrosoi, Phialophora verrucosa, Cladophialophora carrionii.
    • Clinical: Chronic, progressive; verrucous, crusted, warty, “cauliflower-like” plaques/nodules. Often on lower limbs.
    • Diagnosis: Histopathology shows pathognomonic sclerotic bodies (Medlar bodies, “copper pennies”).
    • Treatment: Itraconazole, terbinafine, local heat therapy, surgery.
  • Phaeohyphomycosis:
    • Etiology: Heterogeneous group of pigmented fungi (e.g., Exophiala, Wangiella, Bipolaris).
    • Clinical: Highly variable; subcutaneous cysts/abscesses, sinusitis, keratitis, brain abscess (especially in immunocompromised).
    • Diagnosis: Pigmented (brown/black) septate hyphae, yeast-like cells, or pseudohyphae in tissue; NO sclerotic bodies.
    • Treatment: Surgical excision + antifungals (e.g., itraconazole, voriconazole, amphotericin B). Chromoblastomycosis: clinical, histology, culture

⭐ Sclerotic bodies (Medlar bodies or 'copper pennies') are pathognomonic for chromoblastomycosis and represent fungal cells undergoing cell division by fission.

Mycetoma - Grainy Swellings Saga

Mycetoma foot with sinuses and grains

  • Chronic granulomatous infection: skin, subcutaneous tissue. Often foot (Madura foot), hand.
  • Triad: Painless swelling, multiple sinuses, discharge of grains.
  • Types & Grains:
    • Eumycetoma (fungal): Madurella mycetomatis (black grains). Slower progression.
    • Actinomycetoma (bacterial): Nocardia, Actinomadura (white/yellow/red grains). Faster progression. 📌 "Actino Ants March with Sulfa Drugs" (Actinomycetoma treated with antibiotics like sulfonamides).

⭐ The color of grains discharged from sinuses in mycetoma (e.g., black, white, yellow, red) can provide a clue to the causative organism (eumycetoma vs. actinomycetoma).

  • Dx: Clinical, grain microscopy (KOH, Gram), culture, imaging (X-ray, USG, MRI - "dot-in-circle" sign).
  • Rx:
    • Eumycetoma: Antifungals (e.g., itraconazole) + surgical debridement.
    • Actinomycetoma: Antibiotics (e.g., Welsh regimen: TMP-SMX + Dapsone/Amikacin).

High‑Yield Points - ⚡ Biggest Takeaways

  • Sporotrichosis: "Rose gardener's disease", lymphocutaneous spread along lymphatics; Sporothrix schenckii.
  • Mycetoma: Triad: tumefaction, draining sinuses, grains/granules; Madurella mycetomatis (eumycetoma, black grains).
  • Chromoblastomycosis: Verrucous/warty lesions, pathognomonic sclerotic bodies (Medlar bodies/copper pennies).
  • Rhinosporidiosis: Nasal/ocular friable polyps; R. seeberi showing large sporangia with endospores.
  • Typically from traumatic inoculation of soil fungi; diagnosis by microscopy (KOH, biopsy) & culture.
  • Treatment: Prolonged systemic antifungals (e.g., Itraconazole) often combined with surgical debridement.

Practice Questions: Subcutaneous Mycoses

Test your understanding with these related questions

A patient with AIDS presents with meningitis. India ink staining shows encapsulated yeasts. Which organism is most likely?

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Flashcards: Subcutaneous Mycoses

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Cutaneous involvement in _____ commonly manifests as a verrucous lesion with irregular borders that may mimic squamous cell carcinoma.

Hint: which fungus

TAP TO REVEAL ANSWER

Cutaneous involvement in _____ commonly manifests as a verrucous lesion with irregular borders that may mimic squamous cell carcinoma.

blastomycosis

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