Zygomycosis

Zygomycosis Intro - Fungal Invaders ID

• Causative Agents: Fungi of the Order Mucorales.
• Common Genera:
  • Rhizopus (most frequent)
  • Mucor
  • Lichtheimia (prev. Absidia)
  • Rhizomucor
  • Cunninghamella
• Key Hyphal Features:
  • Broad (5-20 µm), pauciseptate (few septa) or aseptate.
  • Irregular, "ribbon-like" hyphae.
  • Branching often at right angles (approx. 90°).

⭐ Rhizopus arrhizus (formerly R. oryzae) is the predominant species causing human zygomycosis, especially rhino-orbital-cerebral mucormycosis (ROCM).

Zygomycosis Patho - Invasion Secrets

• Entry: Inhalation of sporangiospores into nasal passages/lungs.
• Key Predisposing Factors:
  • Diabetic Ketoacidosis (DKA): Acidic, high-glucose; ↑serum iron.
  • Immunosuppression: Neutropenia, corticosteroids, hematologic malignancies.
  • Iron overload: Deferoxamine (acts as siderophore for Rhizopus).
• Virulence & Invasion:
  • Angioinvasion: Hyphae invade blood vessels, causing thrombosis.
  • Endothelial Adherence: Fungal CotH proteins bind endothelial GRP78.
  • Ketone Reductase: Aids survival in acidic DKA.
  • Rapid Growth & Iron Uptake: Fuels tissue destruction.

⭐ Hallmark: Angioinvasion by hyphae into blood vessels, leading to thrombosis, infarction, and rapid, extensive tissue necrosis.

Zygomycosis Clinical - Disease Faces

• Rhinocerebral (most common, ~50%): Acute sinusitis, facial swelling, bloody nasal discharge, headache, proptosis, vision loss. Black necrotic eschar on palate/nasal turbinates is characteristic.

  • Often in DKA, hematological malignancy.
  • Cranial nerve palsies (III, IV, V, VI, VII).

• Pulmonary (~15-30%): Fever, cough, dyspnea, chest pain, hemoptysis. Angioinvasion leads to infarction, cavitation.

  • Common in neutropenic patients, transplant recipients.

• Cutaneous (~10-15%): Erythema, induration, necrosis. Can be primary (trauma, burns) or secondary (disseminated).

  • Ecthyma gangrenosum-like lesions.

• Gastrointestinal (~5-10%): Abdominal pain, distension, nausea, vomiting, GI bleeding, bowel perforation. Rare, high mortality.

• Disseminated (<5%): Spread to brain, spleen, liver, heart. Poor prognosis.

⭐ Rhinocerebral zygomycosis is the most common form, especially in diabetic ketoacidosis (DKA) patients, presenting with characteristic black necrotic eschar in the nasal cavity or palate. This is a critical diagnostic clue!

Zygomycosis Dx - Spotting the Culprit

• Specimens: Nasal/sinus scrapings, sputum, BAL, deep tissue biopsy (crucial).
• Direct Microscopy (Rapid):
  • 10-20% KOH or Calcofluor white: Broad (6-25µm), pauciseptate/aseptate hyphae.
  • Characteristic: Ribbon-like, irregular, wide-angle (~90°) branching.
• Histopathology (Biopsy): Gold standard. Shows tissue necrosis & angioinvasion by hyphae.
• Culture: Sabouraud Dextrose Agar (SDA) without cycloheximide (inhibits Zygomycetes). Rapid growth ("cottony", "lid lifter"). Species ID (e.g., Rhizopus, Mucor).

⭐ Broad, non-septate (or pauciseptate) hyphae with irregular right-angle branching is a hallmark finding on direct microscopy.

Zygomycosis Rx - Fungus Fight Plan

• Pillars of Management: Rapid diagnosis, aggressive surgical debridement, systemic antifungals, control predisposing conditions.

⭐ Liposomal Amphotericin B is the initial drug of choice; it offers better CNS penetration and reduced nephrotoxicity than conventional AMB.

• Duration: Until clinical/radiological resolution. Consider maintenance if high risk of recurrence.

High‑Yield Points - ⚡ Biggest Takeaways

• Caused by Mucorales order fungi (e.g., Rhizopus, Mucor).
• Features broad, non-septate or pauciseptate hyphae with characteristic right-angle (approx. 90°) branching.
• Strongly associated with diabetic ketoacidosis (DKA), neutropenia, and other immunosuppressive states.
• Rhinocerebral zygomycosis is the most common form, presenting with black necrotic eschar and potential orbital/CNS invasion.
• Diagnosis relies on histopathological examination of biopsy specimens showing invasive hyphae; culture can confirm.
• Management requires urgent surgical debridement of necrotic tissue and systemic Amphotericin B.
• Angioinvasion leading to thrombosis and tissue necrosis is a key pathological feature of the disease process.