Practice 5 structured short- and long-answer medical questions on Weekly Year 3: Medical Mycology Exam - August 21, 2026 (Sections B & C). Review model answe...
Answer: 1. **Azoles (e.g., Fluconazole, Voriconazole):** Inhibit the fungal cytochrome P450 enzyme 14α-demethylase, which is critical for the synthesis of ergosterol from lanosterol. Ergosterol is a vital component of the fungal cell membrane. Inhibition leads to depletion of ergosterol and accumulation of toxic sterol precursors, disrupting membrane fluidity and function. 2. **Polyenes (e.g., Amphotericin B, Nystatin):** Bind directly to ergosterol in the fungal cell membrane, forming pores or channels. This disrupts membrane integrity, leading to increased permeability, leakage of intracellular ions (e.g., K+) and macromolecules, ultimately resulting in cell lysis and death.
Answer: a) Tinea cruris (jock itch). b) *Trichophyton* spp. (e.g., *T. rubrum*, *T. mentagrophytes*) and *Epidermophyton* spp. (e.g., *E. floccosum*). c) Microscopic examination of a KOH-treated skin scraping would typically reveal branching septate hyphae and possibly arthrospores. The hyphae are usually uniform in width.
Answer: 1. **Immunosuppression:** Conditions like HIV/AIDS, organ transplantation, chemotherapy, prolonged corticosteroid use, or hematological malignancies. 2. **Broad-spectrum antibiotic use:** Disrupts the normal bacterial flora, allowing *Candida* species to overgrow. 3. **Indwelling medical devices:** Central venous catheters, urinary catheters, or prosthetic devices provide surfaces for biofilm formation. 4. **Major surgery/Trauma/Burns:** Compromises skin and mucosal barriers, providing entry points for fungi. 5. **Diabetes Mellitus:** Poorly controlled blood glucose provides a favorable environment for fungal growth. 6. **Total Parenteral Nutrition (TPN):** Catheter-related infections are common in patients on TPN.
Answer: a) Mucormycosis (or Zygomycosis). b) *Rhizopus* spp., *Mucor* spp., *Lichtheimia* spp. (previously *Absidia*). c) **Histopathological examination of a biopsy:** This is crucial. It would show characteristic broad, ribbon-like, aseptate or sparsely septate hyphae with irregular branching (typically non-dichotomous) invading blood vessels, leading to angioinvasion, thrombosis, and tissue necrosis. Fungal cultures may be difficult to obtain and can be falsely negative.
Answer: a) Chronic Pulmonary Aspergillosis (CPA) or, less likely but still possible given the cavitating lesion, Semi-invasive Aspergillosis / Invasive Aspergillosis (if profoundly immunocompromised, though COPD and steroids point more to CPA). b) **Key Host Risk Factors:** * **Underlying Lung Disease (COPD):** Pre-existing structural lung damage provides a niche for fungal colonization and growth. * **Long-term Oral Corticosteroid Use:** Corticosteroids are immunosuppressive, impairing host immune responses (e.g., alveolar macrophage function, T-cell activity) that are crucial for clearing fungal pathogens. This allows *Aspergillus* to colonize and invade. * **Advanced Age:** Elderly patients often have diminished immune function. * **Potential for Bronchiectasis/Cavitation:** COPD can lead to structural changes that predispose to fungal colonization. c) **Comprehensive Diagnostic Approach:** * **Clinical Suspicion:** Based on symptoms (chronic cough, weight loss, hemoptysis, fatigue), imaging (cavitation, aspergilloma). * **Radiological Imaging (e.g., Chest CT scan):** To confirm cavitating lesions, identify fungal balls (aspergillomas), pleural thickening, and fibrosis. Halo sign or air crescent sign might be seen in acute invasive forms. * **Mycology (Non-invasive):** * **Serum Galactomannan Assay:** A polysaccharide component of the *Aspergillus* cell wall. Elevated levels suggest invasive disease, but sensitivity can vary, especially in CPA. * **Serum Beta-D-Glucan Assay:** A pan-fungal cell wall component, elevated in most invasive fungal infections (including *Aspergillus*, but also *Candida*, *Pneumocystis*). Less specific than galactomannan for *Aspergillus*. * **Aspergillus Specific Antibodies (IgG, IgE):** Elevated *Aspergillus* IgG antibodies are highly suggestive of CPA. IgE can be elevated in allergic bronchopulmonary aspergillosis (ABPA). * **Mycology (Invasive - if non-invasive tests are inconclusive or for definitive diagnosis):** * **Bronchoscopy with Bronchoalveolar Lavage (BAL):** Direct microscopic examination (KOH stain or Calcofluor white) for fungal hyphae and fungal culture for *Aspergillus* species. Molecular tests (PCR) on BAL fluid are increasingly used. * **Biopsy (Transbronchial, CT-guided percutaneous, or Surgical Lung Biopsy):** **Gold standard for definitive diagnosis.** Histopathological examination demonstrating characteristic septate hyphae with acute angle branching (45 degrees) invading tissue, combined with positive culture. This helps distinguish colonization from invasion. d) **Principles of Initial Medical Management:** * **Antifungal Therapy:** * **First-line:** Oral **Voriconazole** is generally the drug of choice due to its broad spectrum against *Aspergillus* and good oral bioavailability. It requires therapeutic drug monitoring. * **Alternatives:** Isavuconazole, Posaconazole are also active against *Aspergillus* and may be used as alternatives, especially with voriconazole intolerance or resistance. Amphotericin B (lipid formulations preferred) can be used for severe or refractory cases. * **Duration:** Treatment is typically prolonged, often for months to years, especially in CPA, guided by clinical and radiological response. * **Adjunctive Therapies:** * **Corticosteroid Management:** Careful reduction or tapering of immunosuppressive corticosteroids if clinically feasible, as they are a key predisposing factor. This needs to be balanced against the patient's underlying COPD. * **Surgical Intervention:** For patients with localized aspergillomas that are causing significant symptoms (e.g., hemoptysis) and are amenable to resection, surgery may be considered as an adjunct to antifungal therapy, particularly if medical therapy fails or if there is life-threatening hemoptysis. * **Management of Underlying Lung Disease:** Optimization of COPD management to improve lung function and reduce exacerbations. * **Symptomatic Support:** Managing cough, dyspnea, and nutritional support.