Common forms of fungal meningitis

Common forms of fungal meningitis

What are the epidemiology and pathogenesis of common forms of fungal meningitis? 

Fungal meningitis typically results from lymphatic and hematogenous spread from the lungs.

Typically, an immunocompetent host will eliminate the fungus by exhalation. At-risk patients include those with defective cell-mediated immunity due to human immunodeficiency virus (HIV), neutropenia, or immunosuppressive medications such as corticosteroids or cytotoxic chemotherapeutic agents.

A notable exception to this pathogenesis are Candida species since they colonize human mucosa and may enter systemic circulation through both wounds and intravenous catheters.

The epidemiology of central nervous system (CNS) fungal infections is rapidly changing with expanded use of antiretroviral therapy in HIV-infected patients. 

Cryptococcus neoformans remains by far the most common CNS fungal infection, with an annual global incidence of over 1 million cases, resulting in 600,000 deaths.

What are the typical clinical features of fungal meningitis, and how is it diagnosed? 

Fungal meningitis may follow an acute, subacute, or chronic course and commonly presents with fever, headache, and mental status changes.

Focal neurologic symptoms and seizures may develop in the setting of space-occupying lesions.

What is the differential diagnosis of fungal meningitis? 

Fungal meningitis presents with a clinical course and CSF profile similar to that of partially treated bacterial or tuberculous meningitis. Noninfectious considerations include sarcoidosis, Beçhet’s disease, and carcinomatous/lymphomatous meningitis.

What are the expected CSF findings in common types of fungal meningitis? 

The CSF will show a normal to slight elevation in opening pressure with 20 to 500 cells/cc, increased protein, decreased glucose, and a lymphocytic predominance (although Coccidioides immitis and other less common pathogens may show a neutrophil predominance early in the disease course).

Other Diagnostic Testing
Cryptococcus speciesCSF: India ink stain, cryptococcal antigen; stain and culture
Serum: cryptococcal antigen
Other: biopsy of skin lesions
Evacuation by drainage or craniotomyCSF: +/− eosinophilia; serology; stain and culture
Serum: eosinophilia
Histoplasma capsulatumCSF: Histoplasma serology; stain and culture
Blood and urine: histoplasma antigen
Candida speciesCSF: stain and culture
Other: biopsy of skin lesion, culture of catheters

What are some important complications of fungal meningitis? 

Fungal CNS infections typically present as a basilar meningitis and may lead to cranial palsies and optic neuritis.

Patients may also develop communicating hydrocephalus requiring neurosurgical shunt procedures. Patients with mass lesions >3 cm should be considered for surgical debridement.

Such lesions may lead to the development of seizures or focal neurologic deficits. Cryptococcal meningitis is notorious for causing elevated ICP. Serial lumbar punctures may be needed to reduce ICP and prevent irreversible complications of increased ICP such as blindness.

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