CNS fungal Infections

Related Subjects: | Meningococcal Meningitis | Pneumococcal Meningitis | Listerial Meningitis |Herpes Simplex Encephalitis (HSV) |Acute Encephalitis |Toxoplasmosis |Lumbar Puncture |CSF Interpretation |Tuberculosis |TB Meningitis |Chronic and recurrent Meningitiss

⚠️ Critical note: CNS fungal infection is a medical emergency requiring early input from Infectious Diseases / Medical Microbiology and often Neurology, Neurosurgery or ENT. This page is for study purposes only. Always confirm antifungal choice, dose, interactions and monitoring with specialist advice and the BNF.

🧠 About CNS Fungal Infections

• Central nervous system fungal infections include meningitis, meningoencephalitis, cerebral abscesses, granulomas, vascular invasion and extension from adjacent sinuses.
• They are uncommon compared with bacterial and viral CNS infections but are associated with substantial morbidity and mortality.
• Most occur in people with impaired cellular immunity, neutropenia, haematological malignancy, transplantation or corticosteroid exposure, although some fungi can infect apparently immunocompetent patients.
• 🩺 Presentation may be subacute or chronic, so fever and classical meningism may be absent.
• Rapid identification of the organism is important because antifungal susceptibility and CNS penetration vary considerably between drugs.

💡 Think pattern + host:
🍄 Chronic meningitis → Cryptococcus, Histoplasma, Coccidioides.
🧠 Focal lesions / infarcts → think Aspergillus.
👃 Sinus disease + diabetes / ketoacidosis → think mucormycosis.
🏥 Neurosurgery, candidemia or infected CNS device → consider Candida.

🦠 Important Fungal Pathogens

• 🍄 Cryptococcus neoformans / C. gattii
  • Syndrome: usually subacute or chronic meningitis / meningoencephalitis.
  • Risk: advanced HIV, transplantation, corticosteroids and other forms of impaired cellular immunity.
  • C. gattii may also cause disease in apparently immunocompetent individuals.
  • Features: headache, fever, confusion, visual symptoms and cranial nerve palsies.
  • ⚠️ Raised intracranial pressure is particularly important.
• 🌿 Aspergillus species
  • Syndrome: cerebral aspergillosis causing abscesses, haemorrhage, infarction or less commonly meningitis.
  • Risk: prolonged neutropenia, haematological malignancy, stem-cell or solid-organ transplantation and significant immunosuppression.
  • Features: focal neurological deficits, seizures, headache and altered consciousness.
  • 🩸 Angioinvasion can produce thrombosis, cerebral infarction and haemorrhage.
• 🧫 Candida species
  • Syndrome: meningitis, meningoencephalitis, microabscesses or infection of ventricular shunts/devices.
  • Risk: candidemia, neurosurgery, CNS devices, prolonged ICU admission and severe immunosuppression.
  • Features: fever, confusion, headache, seizures or focal neurological abnormalities.
• 🏜️ Coccidioides species
  • Syndrome: chronic basilar meningitis following pulmonary coccidioidomycosis.
  • Geography: endemic particularly in the south-western USA and parts of Mexico and Central/South America.
  • Features: persistent headache, meningism, cranial neuropathies and hydrocephalus.
  • ⚠️ Always ask about travel and residence history.
• 🐦 Histoplasma capsulatum
  • Syndrome: chronic meningitis or focal CNS disease, often with disseminated infection.
  • Risk: immunosuppression and exposure in endemic areas.
  • Environmental exposure includes soil contaminated with bird or bat droppings.
  • Features: headache, fever, cognitive change and cranial neuropathies.
• 👃 Mucorales – mucormycosis
  • Syndrome: usually rhino-orbital-cerebral mucormycosis, spreading from the nasal cavity and paranasal sinuses into the orbit and brain.
  • Risk: uncontrolled diabetes, particularly diabetic ketoacidosis, haematological malignancy, transplantation and corticosteroid exposure.
  • Features: facial pain/swelling, sinusitis, ophthalmoplegia, visual loss, cranial nerve palsies and altered consciousness.
  • ⚠️ Tissue necrosis and a black nasal or palatal eschar are late but important clues.

🩺 Clinical Presentation

• 🤕 Persistent or progressive headache.
• 🌡️ Fever – but this may be absent in profoundly immunocompromised patients.
• 🧠 Confusion, behavioural change, drowsiness or reduced consciousness.
• ⚡ Seizures.
• 👁️ Cranial nerve palsies and visual disturbance.
• 🦵 Focal weakness, sensory loss, dysphasia or cerebellar signs.
• 💡 Photophobia and neck stiffness may occur in fungal meningitis but can be mild or absent.
• 📉 Chronic disease may cause weight loss, malaise and progressive functional decline.

⚠️ Major Risk Factors

• 🦠 Advanced HIV infection.
• 🩸 Neutropenia and haematological malignancy.
• 🧬 Stem-cell or solid-organ transplantation.
• 💊 Prolonged corticosteroids or other immunosuppressive therapy.
• 🍬 Diabetes mellitus, particularly ketoacidosis – strongly associated with mucormycosis.
• 🏥 Neurosurgery, ventricular shunts and other CNS devices.
• 💉 Intravascular catheters and candidemia.
• 🌍 Residence in or travel to endemic fungal regions.
• 🌿 Environmental exposure including disturbed soil, construction dust and bird/bat-contaminated environments.

🔬 Diagnosis & Investigations

⚠️ Do not delay treatment in a critically ill high-risk patient while waiting for definitive fungal identification. However, obtaining good microbiological and histological samples is crucial because treatment differs markedly between fungal species.

• 🩸 Blood:
  • FBC including neutrophil count.
  • U&E, renal function, magnesium and LFTs – important both diagnostically and before antifungal treatment.
  • CRP ± ESR.
  • Blood cultures, including fungal culture where appropriate.
  • HIV testing unless already known.
• 💉 CSF:
  • Measure opening pressure.
  • Cell count and differential.
  • Protein and paired CSF/blood glucose.
  • Fungal microscopy and culture.
  • Cryptococcal antigen in suspected cryptococcosis.
  • Specific fungal antigen, antibody or molecular testing depending on the clinical setting and laboratory availability.
• 🍄 Cryptococcus:
  • CSF cryptococcal antigen (CrAg) is highly important diagnostically.
  • Serum CrAg is also useful, particularly in disseminated disease.
  • India ink microscopy may demonstrate encapsulated yeast but is less sensitive than antigen testing.
  • CSF may show lymphocytic pleocytosis, raised protein and low glucose, but abnormalities may be surprisingly mild in advanced immunosuppression.
• 🧠 Imaging:
  • Contrast-enhanced MRI brain is usually the most sensitive investigation for CNS fungal disease.
  • Possible findings include abscesses, granulomas, meningeal enhancement, infarction, haemorrhage and hydrocephalus.
  • CT is useful when MRI is unavailable or contraindicated and is particularly valuable for assessing sinus and bony disease.
• 🫁 Search for extracranial infection:
  • CT chest may demonstrate pulmonary aspergillosis, cryptococcosis or endemic fungal disease.
  • CT sinuses/orbits is essential when rhino-orbital fungal infection is suspected.
• 🔬 Tissue diagnosis:
  • Biopsy may be essential, particularly for Aspergillus and Mucorales.
  • Send tissue for histopathology, fungal microscopy, culture and molecular identification where available.
  • ⚠️ Culture can be negative despite histological evidence of invasive fungal disease.

💊 Treatment – Overview

🍄 Cryptococcal Meningitis

• Initial therapy usually includes liposomal amphotericin B + flucytosine, followed by fluconazole consolidation and maintenance.
• Exact regimens differ according to HIV status, transplantation status, immune function and local resources.
• 📏 Measure CSF opening pressure at lumbar puncture.
• Raised intracranial pressure is a major cause of morbidity and mortality.
• 💉 Symptomatic raised pressure may require repeated therapeutic lumbar punctures.
• CSF diversion may be required when pressure cannot be adequately controlled.
• ⚠️ Mannitol, acetazolamide and routine corticosteroids are not substitutes for therapeutic CSF drainage.
• In HIV-associated cryptococcal meningitis, the timing of ART requires specialist consideration because starting ART too early can increase the risk of severe immune reconstitution inflammatory syndrome (IRIS).

🌿 CNS Aspergillosis

• Voriconazole is generally preferred as first-line treatment because of efficacy and CNS penetration.
• Liposomal amphotericin B may be used when voriconazole is contraindicated, not tolerated or ineffective.
• 🧪 Drug interactions and therapeutic drug monitoring are important with voriconazole.
• Surgical resection or drainage may be considered for accessible focal lesions, diagnostic uncertainty or mass effect.
• Where possible, reverse underlying immunosuppression or neutropenia.

🧫 CNS Candidiasis

• Initial treatment generally involves liposomal amphotericin B ± flucytosine.
• Fluconazole may be used as step-down therapy once there has been clinical response and the isolate is susceptible.
• ⚠️ Echinocandins are not recommended as standard therapy for CNS candidiasis because therapeutic CNS concentrations are unreliable.
• Remove infected ventricular shunts or other CNS devices where possible.
• Treatment usually continues until clinical, CSF and radiological abnormalities have resolved.

🏜️ Coccidioidal Meningitis

• Fluconazole is generally first-line therapy.
• Higher doses than those used for uncomplicated mucosal fungal infections are required.
• Itraconazole or other azoles may be considered in selected cases under specialist guidance.
• Intrathecal amphotericin B may be considered for refractory disease in specialist centres.
• ♾️ Treatment of coccidioidal meningitis is generally lifelong because relapse after stopping therapy is common.
• Hydrocephalus is a common complication and may require neurosurgical CSF diversion.

🐦 CNS Histoplasmosis

• Treatment usually begins with liposomal amphotericin B.
• This is followed by prolonged itraconazole therapy.
• Treatment is typically prolonged and guided by clinical, CSF and imaging response.
• Look for evidence of disseminated histoplasmosis.

👃 Rhino-Orbital-Cerebral Mucormycosis

• 🚨 This is an immediately life-threatening emergency.
• Start high-dose liposomal amphotericin B promptly.
• 🔪 Early aggressive surgical debridement of necrotic tissue is often essential.
• Isavuconazole or posaconazole may be used in selected circumstances, including salvage or intolerance, with specialist advice.
• Correct reversible risk factors:
• 🍬 Rapidly control hyperglycaemia and ketoacidosis.
• 💊 Reduce corticosteroid exposure where clinically possible.
• 🩸 Attempt to reverse neutropenia where appropriate.

⚕️ General Management Principles

• ☎️ Seek early specialist infectious-disease / microbiology advice.
• 🍄 Begin appropriate systemic antifungal therapy promptly.
• 🔬 Obtain cultures and tissue diagnosis wherever feasible.
• 🧪 Perform fungal susceptibility testing where appropriate.
• 💊 Review drug interactions – azoles have particularly important interactions.
• 🩸 Monitor renal, hepatic and haematological toxicity.
• ⚡ Treat seizures.
• 📏 Identify and actively manage raised intracranial pressure.
• 🔪 Consider neurosurgical, ENT or ophthalmological intervention when indicated.
• 🛡️ Reduce immunosuppression where safe and clinically appropriate.
• 🦠 Optimise HIV therapy with specialist guidance.

💊 Important Antifungal Toxicities

• Amphotericin B: nephrotoxicity, potassium/magnesium loss, infusion reactions and anaemia.
• Flucytosine: bone-marrow suppression and hepatotoxicity – levels may require monitoring.
• Voriconazole: hepatotoxicity, visual disturbance, photosensitivity, QT effects and many drug interactions.
• Fluconazole: hepatotoxicity, QT prolongation and drug interactions.
• Itraconazole: hepatotoxicity, substantial drug interactions and negative inotropic effects.
• Isavuconazole: hepatotoxicity and drug interactions; unlike many other azoles it may shorten the QT interval.

💡 Exam pearl: antifungal drugs are not interchangeable. Drug choice depends on the fungus, susceptibility pattern, CNS penetration and patient factors. For example, an echinocandin may be useful for candidemia but is generally not adequate treatment for CNS candidiasis.

🛡️ Prevention

• Use antifungal prophylaxis only in defined high-risk populations according to local haematology/transplant protocols.
• Minimise unnecessary corticosteroid and broad-spectrum antimicrobial exposure.
• Optimise glycaemic control.
• Careful management and prompt removal of infected intravascular or CNS devices.
• High-risk profoundly immunocompromised patients should avoid significant exposure to construction dust and aerosolised mould spores.
• Consider geographical exposures when counselling markedly immunocompromised travellers.

📉 Prognosis

• Outcome depends on the organism, fungal burden, speed of diagnosis and degree of underlying immunosuppression.
• 🍄 Cryptococcosis: potentially curable, but neurological complications and raised ICP substantially influence outcome.
• 🌿 CNS aspergillosis: remains associated with high mortality, particularly in persistent neutropenia or severe immunosuppression.
• 🧫 CNS candidiasis: uncommon but serious; device-associated infection requires source control.
• 👃 Cerebral mucormycosis: carries a very high mortality; rapid antifungal therapy plus surgery provides the best chance of survival.
• 🏜️ Coccidioidal meningitis: can often be suppressed effectively but usually requires lifelong therapy.

🧠 Key Learning Points

🍄 Cryptococcus → chronic meningitis + raised ICP → amphotericin + flucytosine, then fluconazole.
🌿 Aspergillus → abscesses, infarction and haemorrhage from angioinvasion → voriconazole.
🧫 Candida CNS disease → amphotericin ± flucytosine; avoid relying on echinocandins.
🏜️ Coccidioidal meningitis → fluconazole and usually lifelong therapy.
👃 Mucormycosis → diabetes/DKA + sinus/orbital disease → urgent amphotericin + surgical debridement.
🔬 In invasive mould infection, tissue diagnosis is extremely valuable.
⚠️ Always consider drug toxicity, interactions and the need to reverse underlying immunosuppression.

📚 References

• Chang CC, et al. Global guideline for the diagnosis and management of cryptococcosis. Lancet Infect Dis. 2024.
• Patterson TF, et al. Practice Guidelines for the Diagnosis and Management of Aspergillosis. Clin Infect Dis. 2016.
• Pappas PG, et al. Clinical Practice Guideline for the Management of Candidiasis. Clin Infect Dis. 2016.
• Cornely OA, et al. Global guideline for the diagnosis and management of mucormycosis. Lancet Infect Dis. 2019.
• Galgiani JN, et al. Clinical Practice Guideline for the Treatment of Coccidioidomycosis. Clin Infect Dis. 2016.
• British National Formulary. Antifungal drugs. Current edition.