Fungal Infections — Written Clinical Reasoning

SAQ 1 — Integrated Management of Invasive Pulmonary Aspergillosis (20 marks, 30 minutes)

Prompt: Outline your integrated management plan for this patient with invasive pulmonary aspergillosis complicating AML induction, including: (a) the diagnostic reasoning that establishes the diagnosis and the EORTC/MSG framework you are applying; (b) the first-line antifungal therapy with exact agent, dose, route, monitoring, and the trial evidence that supports it; (c) the adjunctive measures beyond antifungal therapy; (d) the duration of therapy and the criteria for response; (e) the plan for secondary prophylaxis and the implications for his subsequent chemotherapy; and (f) the high-yield exam traps in invasive aspergillosis management. [4]

Model Answer

(a) Diagnostic reasoning and the EORTC/MSG framework (3 marks): [4]

This patient meets the EORTC/MSG criteria for probable invasive pulmonary aspergillosis — a host factor (prolonged neutropenia above 10 days after AML induction), a clinical feature (a new pulmonary nodule with the halo sign on CT), and mycological evidence (a positive serum galactomannan above 0.5 and a positive BAL galactomannan) [1]. The halo sign — a nodule surrounded by a ground-glass halo of haemorrhage — is the early radiological signature of angioinvasive aspergillosis, reflecting haemorrhagic infarction around a focus of fungal growth; it is most sensitive in the first week. The chest X-ray was unremarkable because the radiographic findings lag behind the CT findings and the clinical disease — the chest X-ray must never be accepted as exclusion of invasive mould infection in the neutropenic patient. A positive serum galactomannan in this host and with this imaging is sufficient to treat without biopsy, though tissue confirmation is the gold standard where feasible (showing septate hyphae branching at acute angles with tissue invasion).

(b) First-line antifungal therapy (5 marks): [1]

The first-line therapy is voriconazole, established by the Herbrecht 2002 randomised trial which showed a higher response rate (52.8 per cent vs 31.6 per cent) and a survival benefit (70.8 per cent vs 57.9 per cent at 12 weeks) over amphotericin B deoxycholate [2]. The regimen is voriconazole 6 mg/kg intravenously every 12 hours for two loading doses, then 4 mg/kg every 12 hours, transitioning to oral voriconazole 200 to 300 mg every 12 hours once the patient can absorb (bioavailability above 90 per cent). I will monitor the voriconazole trough level (target 1 to 5.5 mg/L) after 4 to 7 days, because voriconazole has nonlinear pharmacokinetics, is metabolised by CYP2C19 (which is highly polymorphic), and has wide inter-patient variability — both subtherapeutic and supratherapeutic levels are common. The main adverse effects are a transient visual disturbance (bright lights, altered colour perception, above 20 per cent and usually reversible), hepatotoxicity, and with prolonged use photosensitivity and a signal for squamous cell carcinoma of the skin. Isavuconazole is a non-inferior alternative established by the SECURE randomised trial [3] with a cleaner safety profile, predictable pharmacokinetics (no routine monitoring), and unique QT-shortening; it is preferred where drug interactions or voriconazole intolerance are a concern. Liposomal amphotericin B is an alternative for pregnancy (voriconazole is teratogenic) or intolerance.

(c) Adjunctive measures beyond antifungal therapy (3 marks): [4]

The single most important adjunct to the antifungal is immune recovery. I will work with the haematology team to reduce the immunosuppression where possible (reduce any corticosteroids, taper calcineurin inhibitors if applicable), support neutrophil recovery, and consider G-CSF in selected patients with profound and prolonged neutropenia and invasive fungal infection (this is a recognised but not routine indication). I will manage the underlying metabolic derangements, monitor for complications (massive haemoptysis is a life-threatening complication of cavitary disease near great vessels and may require bronchial artery embolisation or surgical resection; cerebral involvement demands imaging and prolonged therapy). I will screen for other opportunistic infections, continue PJP prophylaxis, and ensure adequate nutrition. [4]

(d) Duration of therapy and criteria for response (3 marks): [4]

The duration of treatment is a minimum of 6 to 12 weeks, guided by the clinical and radiological response, the serial galactomannan trend, and the recovery of immune function. I will monitor the galactomannan every 1 to 2 weeks (a falling titre supports response; a rising titre suggests progressive disease or resistance), repeat the chest CT at 4 to 6 weeks to assess radiological response (cavitation, air-crescent sign formation, contraction of the lesion), and follow the clinical picture (resolution of fever, cough, and pleuritic pain). Recovery of the neutrophil count is the single strongest predictor of survival from invasive aspergillosis. I will not stop therapy prematurely on the basis of a single negative galactomannan — the decision to stop is a composite one based on clinical, radiological, mycological, and immunological recovery. [4]

(e) Secondary prophylaxis and implications for subsequent chemotherapy (3 marks): [4]

Once the acute infection is controlled, this patient will need mould-active secondary prophylaxis (posaconazole or voriconazole) through every subsequent neutropenic chemotherapy cycle and through any allogeneic haematopoietic stem cell transplant, because a prior episode of invasive aspergillosis confers a very high risk of recurrence with the next immunosuppressive phase. The timing of the next chemotherapy cycle is a multidisciplinary decision with haematology — invasive aspergillosis is a relative contraindication to immediate further intensive chemotherapy because it will prolong the neutropenia and worsen the fungal infection; a bridging strategy, a delayed consolidation, or a less myelosuppressive regimen may be appropriate. If he is a candidate for allogeneic transplant, the aspergillosis must be controlled before conditioning begins, and antifungal prophylaxis continues through the transplant. I will communicate the plan clearly to the patient, the haematology team, and the general practitioner. [4]

(f) High-yield exam traps (3 marks): [1]

The traps are: (1) choosing amphotericin B as first-line for aspergillosis — voriconazole is first-line on the Herbrecht survival benefit; amphotericin is the alternative; (2) accepting a normal chest X-ray as exclusion of invasive aspergillosis — the chest CT is the test that finds the halo sign; (3) treating mucormycosis with voriconazole — voriconazole has no activity against Mucorales; (4) forgetting therapeutic drug monitoring of voriconazole — the levels vary widely and both subtherapeutic and toxic levels are common; (5) stopping antifungal therapy prematurely — the duration is 6 to 12 weeks guided by composite response; (6) missing the distinction between the halo sign (Aspergillus, early) and the reverse halo / atoll sign (Mucorales, early) — both occur in neutropenic hosts but the antifungal differs; (7) confusing serum galactomannan (for Aspergillus) with serum beta-D-glucan (for Candida, Aspergillus, and PJP, but not Cryptococcus or Mucorales) — the spectrum and the false positives differ. [4]

SAQ 2 — Candidaemia in the Post-Operative ICU Patient: Source Control and Drug Choice (10 marks)

Prompt: A 56-year-old man in the ICU on day 10 after small bowel perforation repair, with a central venous catheter, broad-spectrum antibiotics, and total parenteral nutrition, develops fever and hypotension. Two peripheral blood cultures grow Candida species (speciation pending). He is in septic shock on noradrenaline 0.2 micrograms/kg/minute. Outline: (a) the immediate empiric antifungal therapy with exact agent, dose, and route, and why; (b) the essential source control measures; (c) the role of the dilated fundoscopy and when it must be performed; (d) the duration of therapy and the criteria for stopping; and (e) how your approach would change if the speciation returned as C. parapsilosis rather than C. glabrata. [4]

Model Answer

(a) Immediate empiric antifungal therapy (2 marks): [1]

The immediate therapy is an echinocandin — caspofungin 70 mg loading then 50 mg daily, micafungin 100 mg daily, or anidulafungin 200 mg loading then 100 mg daily — all intravenously. The IDSA 2016 candidiasis guideline recommends an echinocandin as first-line for the unstable or critically ill patient with candidaemia, the neutropenic patient, the patient with recent azole exposure, and where C. glabrata or C. krusei is plausible [4]. The echinocandins are fungicidal against Candida (the azoles are fungistatic), they cover the fluconazole-resistant species (C. glabrata, C. krusei), and they have a clean safety profile with minimal drug interactions. The Reboli randomised trial of anidulafungin versus fluconazole showed a higher response rate for anidulafungin, particularly in the more severely ill [5]. Fluconazole would be inappropriate here because of the septic shock and the unresolved speciation.

(b) Essential source control measures (2 marks): [1]

The central venous catheter must be removed as soon as possible. The IDSA guideline is explicit — catheter removal is strongly recommended in non-neutropenic patients with candidaemia, because the catheter is the source or a reservoir in the majority and leaving it in situ prolongs fungaemia and increases metastatic seeding (endophthalmitis, endocarditis). If there is a recognised intra-abdominal source (abscess, leak), it must be drained or revised. Source control is as important as the antifungal choice. [4]

(c) The dilated fundoscopy (2 marks): [1]

A dilated fundoscopy by an ophthalmologist is mandatory in every patient with candidaemia, ideally within the first week. Candidal endophthalmitis — white, fluffy chorioretinal lesions with vitritis — is present in up to 15 per cent of candidaemic patients, can be sight-threatening, and changes the management: extended therapy (4 to 6 weeks minimum), intravitreal amphotericin or echinocandin, and vitrectomy in severe disease. Missing it is a recognised and preventable cause of visual loss and a favourite exam discriminator. [4]

(d) Duration of therapy and criteria for stopping (2 marks): [4]

The duration is 14 days from the first negative blood culture, provided the patient has clinically responded, the central line has been removed (or the source controlled), there is no metastatic focus (endophthalmitis, endocarditis, osteomyelitis, hepatosplenic disease), and repeat blood cultures after line removal are negative. Once the patient has clinically improved, the Candida species is identified and susceptible, and cultures are negative, step down to oral fluconazole (or voriconazole for C. krusei) to complete the course. If endocarditis is present, the duration extends to at least 6 weeks and often longer, with surgical evaluation for valve replacement. [4]

(e) C. parapsilosis rather than C. glabrata (2 marks): [1]

C. parapsilosis is associated with central lines and parenteral nutrition and is generally less virulent than C. albicans or C. glabrata. It has reduced susceptibility to the echinocandins in some regions, so if the isolate is fluconazole-susceptible, fluconazole may be preferred for step-down or even initial therapy if the patient is stable. C. glabrata, by contrast, is often fluconazole-resistant and the echinocandin is maintained throughout, with step-down only to high-dose fluconazole or voriconazole if the isolate is documented susceptible. The speciation and the susceptibility therefore determine the step-down and the overall strategy. The source control (line removal) and the fundoscopy are unchanged regardless of the species. [4]