Respiratory mycosis for md exams 10 marks answer from fishman and murray only
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I now have very comprehensive content from both Fishman and Murray. I have enough to write a complete, high-quality 10-mark answer covering all the major respiratory mycoses. Let me compile this now.
Respiratory Mycoses
(Fishman's Pulmonary Diseases & Disorders + Murray & Nadel's Textbook of Respiratory Medicine)
INTRODUCTION
Respiratory (pulmonary) mycoses are fungal infections of the lungs caused by a diverse group of organisms. They are broadly classified into:
- Endemic (dimorphic) mycoses - Histoplasma, Coccidioides, Blastomyces
- Opportunistic mycoses - Aspergillus, Mucorales, Cryptococcus, Pneumocystis, Candida, Talaromyces
Fishman notes that pulmonary mycoses represent an emerging disease burden in the rapidly expanding population of immunocompromised patients. In endemic areas, dimorphic fungi account for up to 30% of community-acquired pneumonia, with direct healthcare costs from histoplasmosis, blastomycosis, and coccidioidomycosis alone approaching $500 million annually in the US.
I. ENDEMIC (DIMORPHIC) MYCOSES
A. HISTOPLASMOSIS (Histoplasma capsulatum)
Epidemiology: Dimorphic, soil-dwelling fungus; found on all continents except Antarctica. Most common in the Mississippi, Ohio, and St. Lawrence River valleys (North America). Soil enriched by bird or bat excrement promotes sporulation.
Mycology: In soil - mycelial form with characteristic tuberculate macroconidia and microconidia. In the human host (at 37°C) - transforms to yeast form. Microconidia are easily aerosolized and inhaled into alveoli.
Pathogenesis (Fishman): After alveolar deposition, H. capsulatum transforms to yeast form → local pneumonitis → spreads to regional lymph nodes and reticuloendothelial organs before cell-mediated immunity develops. Two to three weeks after exposure, a flulike syndrome with fever, chills, myalgias, nonproductive cough, and chest pain develops in about 40% of immunocompetent individuals. 99% resolve spontaneously.
Pulmonary Syndromes (Fishman, Table 133-4):
| Syndrome | Age | Course | Radiograph | Treatment |
|---|---|---|---|---|
| Acute | Any | 1-2 weeks | Diffuse interstitial/reticulonodular, miliary pattern | Only if severe/prolonged |
| Subacute | Any | Weeks-months | Focal airspace disease, lymphadenopathy | If symptoms >1 month |
| Chronic | >45 y | Months-years | Focal, upper lobe cavitary, thick-walled bullae, emphysema | Yes (itraconazole) |
| Progressive disseminated | Immunocompromised | 1-2 weeks | Diffuse airspace opacities | Amphotericin B |
| Mediastinal fibrosis | 20-30 y | Late | Homogeneous mass, obstructing airways/vessels, extensive calcifications | If hemoptysis or obstruction |
Diagnosis (Murray): Urinary/serum Histoplasma antigen (most sensitive in disseminated disease); BAL antigen + cytopathology; blood fungal cultures (90% positive in disseminated disease). Serology (complement fixation, immunodiffusion) useful in isolated pulmonary disease. False positives seen with blastomycosis, coccidioidomycosis, paracoccidioidomycosis.
Treatment (Murray): Amphotericin B lipid formulation (3 mg/kg/day) for moderate-severe disease; itraconazole for mild disease. Echinocandins have no activity against Histoplasma. Minimum 12-month course for disseminated disease.
B. COCCIDIOIDOMYCOSIS (Coccidioides immitis / C. posadasii)
Epidemiology: Endemic to semiarid southwestern United States (central California, southern Arizona), northern Mexico, and central Argentina. California's southern San Joaquin Valley is hyperendemic.
Mycology (Murray): In soil - mycelial form with arthrospores (arthroconidia). After inhalation and deposition in alveoli, arthrospores transform into spherules containing several hundred endospores. Rupture of spherules releases endospores → each forms new spherules (the tissue cycle).
Clinical Features (Murray): Chief manifestation - mild flulike, often undiagnosed illness from which most healthy people spontaneously recover. Chronic pulmonary disease in ~5%; disseminated disease in even fewer. In HIV: focal or diffuse pneumonia, cutaneous disease, meningitis, dissemination. Presenting symptoms: fever and chills (68%), night sweats (36%), weight loss.
Diagnosis: Serology (IgM and IgG antibodies); culture (biohazard level 3); spherules on histology (H&E); Coccidioides antigen test. Chest CT shows nodules, consolidation, or cavities.
Treatment (Fishman): Mild-moderate pulmonary disease - fluconazole 400 mg/day for 6-12 months. Severe disease - amphotericin B-based therapy. Alternatives: posaconazole, voriconazole, isavuconazole, itraconazole. Meningitis requires lifelong fluconazole.
C. BLASTOMYCOSIS (Blastomyces dermatitidis)
Epidemiology (Murray): Coendemic with histoplasmosis throughout central United States; less common than histoplasmosis.
Mycology: Dimorphic fungus. Distinctive yeast form: broad-based budding with thick cell wall, single bud (hallmark feature). In tissue at 37°C, yeast form with characteristic "figure-of-8" appearance.
Clinical Features (Murray): In HIV: two patterns - (1) disease limited to respiratory system; (2) disseminated blastomycosis. Abnormal chest radiographs in 73%; diffuse interstitial or miliary disease is most common radiographic finding (55%). Definitive diagnosis requires culture of B. dermatitidis; visualization of characteristic budding yeast is strongly suggestive.
Treatment: IV amphotericin B for severe disease → step-down to oral itraconazole for at least 12 months. Mortality in disseminated disease: 40% at 30 days despite therapy.
II. OPPORTUNISTIC MYCOSES
A. PULMONARY ASPERGILLOSIS (Aspergillus species, mainly A. fumigatus)
Fishman states: Aspergillus is a ubiquitous saprophytic mold with high sporulating capacity, releasing conidia at 1-100 conidia/m³ into the atmosphere. Conidia are 2-3 µm - small enough to reach alveoli.
Spectrum of Disease (Fishman, Table 132-1) - depends on immune status:
| Form | Host | Mechanism |
|---|---|---|
| Simple colonization | Normal/COPD | No invasion |
| Allergic asthma | Atopic | IgE-mediated bronchospasm |
| ABPA | Asthma/CF | Th2-mediated hypersensitivity |
| Chronic pulmonary aspergillosis (CPA) | Pre-existing cavities (post-TB) | Saprophytic growth |
| Aspergilloma | Pre-existing cavities | Fungal ball |
| Invasive pulmonary aspergillosis (IPA) | Immunocompromised | Angioinvasion |
1. Allergic Bronchopulmonary Aspergillosis (ABPA) (Fishman):
- Affects 7-14% of poorly controlled asthmatics and 7-9% of CF patients.
- Immunopathogenesis: Genetically susceptible atopic individuals → A. fumigatus-specific Th2 CD4+ cell hyperactivation → IgE-mediated mast cell degranulation → IgG-Aspergillus immune complexes → complement activation → pulmonary damage.
- HLA associations: HLA-DR2 and HLA-DR5 alleles confer susceptibility.
- Rosenberg-Patterson Stages:
- Stage I (Acute): fever, productive cough, wheezing; eosinophilia, elevated total IgE, positive skin test; consolidation/mucoid impaction on chest X-ray
- Stage II (Remission): asymptomatic; normal chest X-ray; declining IgE
- Stage III (Exacerbation): recurrence; doubling of IgE from baseline
- Stage IV (Corticosteroid-dependent): steroid-requiring asthma
- Stage V (Fibrotic): pulmonary fibrosis; irreversible obstruction
- Treatment: Oral corticosteroids (mainstay - achieve remission); itraconazole (steroid-sparing); omalizumab (reduces exacerbations in placebo-controlled trial); monitor serum total IgE every 1-2 months.
2. Chronic Pulmonary Aspergillosis (CPA): Indolent course in patients with subtle immune defects or pre-existing cavities. Low-grade chronic inflammation, progressive cavitary or fibrotic lesions, minimal parenchymal invasion.
3. Invasive Pulmonary Aspergillosis (IPA) (Fishman):
- Most severe form; occurs in immunocompromised (prolonged neutropenia, high-dose steroids, SOT, HSCT, CGD).
- Pathology: Conidia germinate → hyphae → angioinvasion → hemorrhagic infarction.
- CT findings: Nodule with halo sign (rim of ground-glass attenuation around central nodule - due to hemorrhage); air crescent sign (late sign, indicates recovery); cavitation; consolidation.
- Diagnosis (Murray): BAL galactomannan (sensitivity 77-100% with cutoff 0.5); serum galactomannan less reliable in solid organ transplant recipients; BAL culture sensitivity only 45-62% in SOT. Bronchoscopy with BAL; surgical biopsy for definitive diagnosis.
- Treatment (Murray): Voriconazole is first-line therapy. Addition of echinocandin (e.g., caspofungin) for severe/progressive disease. Inhaled amphotericin B recommended as adjunct for airway infections. Isavuconazole is an alternative.
B. MUCORMYCOSIS (Mucorales)
Organisms: Rhizopus, Mucor, Lichtheimia (Absidia), Cunninghamella.
Risk Factors: Prolonged neutropenia, diabetic ketoacidosis, deferoxamine therapy, iron overload states, SOT, HSCT.
Pathogenesis (Fishman): Mucorales cause severe, frequently fatal angioinvasive infections. Characterized by hyphal invasion of blood vessel walls → thrombosis → tissue infarction and necrosis. Unlike Aspergillus, hyphae are broad, pauciseptate, and ribbon-like with right-angle branching (vs. Aspergillus: narrow, septate, 45° branching).
Pulmonary Mucormycosis: Chest CT shows nodules, consolidation, cavitation; the reversed halo sign (central consolidation with surrounding ground-glass) has been described. Angioinvasion leads to hemoptysis, pulmonary infarction, and rapid progression.
Treatment: Liposomal amphotericin B (first-line); surgical debridement of necrotic tissue; reversal of underlying immunosuppression. Isavuconazole is an alternative. Voriconazole has no activity against Mucorales (important distinction from aspergillosis).
C. CRYPTOCOCCOSIS (Cryptococcus neoformans / C. gattii)
Mycology (Murray): Encapsulated yeast with polysaccharide capsule detectable by India ink (negative staining - clear halo around budding yeast) or mucicarmine staining. Transmitted by aerosol. C. neoformans - global distribution, isolated from bird excrement, decaying fruit, soil. C. gattii - Australia, South America, Pacific Northwest of US. Most HIV-associated disease due to C. neoformans.
Epidemiology (Fishman): In 2017, 6% of HIV-positive persons with CD4+ <100 cells/mm³ had positive cryptococcal antigenemia. In non-HIV hosts, up to 20% of Cryptococcus infections occur without identifiable immune deficits.
Pulmonary Manifestations (Fishman):
- Lung is the primary portal of entry.
- Immunocompetent hosts: isolated asymptomatic pulmonary infection is common; nodular infiltrates may be found incidentally.
- Immunocompromised (especially PLWH): meningoencephalitis is the most common severe manifestation; pulmonary disease can present as pneumonia, nodules, consolidation, or ARDS.
- IRIS (immune reconstitution inflammatory syndrome): cavitation of nodules or new intrathoracic adenopathy after ART initiation.
Diagnosis: Serum cryptococcal antigen (CrAg) - highly sensitive and specific; India ink of CSF; culture.
Treatment (Fishman):
- Pulmonary (mild-moderate): Fluconazole 400 mg/day for 6-12 months.
- Meningitis (PLWH): Amphotericin B deoxycholate (0.7-1.0 mg/kg/day) OR liposomal amphotericin B (3-4 mg/kg/day) PLUS flucytosine (100 mg/kg/day in 4 divided doses) for at least 2 weeks (induction) → fluconazole 400 mg/day × 8 weeks (consolidation) → fluconazole 200 mg/day (maintenance until CD4 >100 and viral load suppressed for ≥3 months).
- ACTA Trial (2018) - Molloy et al. (Fishman): n=721, randomized; 1 week amphotericin B + flucytosine showed 10-week mortality of 24% - lowest of all arms; flucytosine clearly superior to fluconazole as combination partner.
Prevention (Murray): Serum CrAg screening for HIV-infected individuals with CD4+ <100 cells/µL in high-burden countries; preemptive fluconazole significantly reduces mortality. Primary prophylaxis not recommended in the US.
D. PNEUMOCYSTIS PNEUMONIA (PCP) (Pneumocystis jirovecii)
Treatment (Murray, Table 123.2):
- Mild PCP (PaO₂ >70 mmHg and A-a gradient <35 mmHg):
- TMP-SMX: 15-20 mg/kg/day (TMP component) q6-8h (oral preferred for outpatients)
- Alternatives: TMP + dapsone; clindamycin + primaquine; atovaquone 750 mg TID
- Moderate-Severe PCP (PaO₂ ≤70 mmHg OR A-a gradient ≥35 mmHg):
- TMP-SMX: 15-20 mg/kg/day IV (preferred route until improvement)
- Pentamidine: 3-4 mg/kg IV once daily
- Clindamycin 1800-2400 mg/day + primaquine 30 mg (base) daily
- Adjunctive corticosteroids (prednisone 40 mg PO BID × 5 days, then 40 mg OD × 5 days, then 20 mg OD × 11 days) - for moderate-severe PCP
- Duration: 21 days for all regimens.
E. TALAROMYCOSIS (Talaromyces marneffei, formerly Penicillium marneffei)
(Murray): Endemic in Southeast Asia; third most common opportunistic infection in Thailand (after TB and cryptococcosis), accounting for 15-20% of AIDS-related illnesses. Dimorphic, soil-dwelling; infection likely acquired by inhalation, related to soil exposure during rainy season (May-October). CD4+ usually <100 cells/µL. Clinical: fever, weight loss, cough; generalized papular skin lesions with central umbilication (characteristic). Diagnosis: blood/bone marrow culture; yeast-laden macrophages on microscopy; galactomannan assay may cross-react positively. Treatment: amphotericin B followed by itraconazole.
KEY DIAGNOSTIC STAINS (Fishman, Fig. 133-2)
| Organism | Diagnostic Stain/Test |
|---|---|
| Cryptococcus | India ink (negative stain), mucicarmine, PAS |
| Histoplasma | H&E (intracellular yeast in macrophages), GMS, PAS |
| Aspergillus | GMS (45° branching septate hyphae) |
| Mucorales | H&E (broad pauciseptate ribbon-like hyphae) |
| PCP | GMS, Giemsa (cysts/trophozoites in BAL) |
KEY TREATMENT SUMMARY
| Organism | First-Line | Alternative | Do NOT Use |
|---|---|---|---|
| Histoplasma (severe) | Liposomal AmB | Itraconazole (mild) | Echinocandins |
| Coccidioides (pulmonary) | Fluconazole 400 mg × 6-12 months | Amphotericin B (severe) | - |
| Blastomyces (severe) | IV Amphotericin B → itraconazole | - | - |
| Aspergillus (IPA) | Voriconazole | Isavuconazole, AmB | Fluconazole |
| Mucorales | Liposomal AmB + surgery | Isavuconazole | Voriconazole |
| Cryptococcus (meningitis) | AmB + flucytosine × 2 weeks → fluconazole | - | Echinocandins |
| PCP | TMP-SMX | Pentamidine, clindamycin+primaquine | - |
| Talaromyces | AmB → itraconazole | - | - |
Sources:
- Fishman's Pulmonary Diseases and Disorders (9781260473940), Chapters 132 (Aspergillus, Candida, and Opportunistic Mycoses) and 133 (Cryptococcosis and the Endemic Mycoses)
- Murray & Nadel's Textbook of Respiratory Medicine (9780323655873), Chapters on Fungal Infections in HIV (Block 28) and Lung Transplantation (Block 33), including PCP treatment tables (Table 123.2)
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