ESSENTIALS OF DIAGNOSIS
Most common cause of fungal meningitis.
Predisposing factors: chemotherapy for hematologic malignancies, Hodgkin lymphoma, corticosteroid therapy, transplant recipients, TNF-alpha inhibitor therapy, and HIV infection.
Headache, abnormal mental status; meningismus seen occasionally, though rarely in HIV-infected patients.
Demonstration of capsular polysaccharide antigen or positive culture in CSF is diagnostic.
Cryptococcosis is mainly caused by Cryptococcus neoformans, an encapsulated budding yeast that has been found worldwide in soil and on dried pigeon dung. C gattii is a closely related species that also causes disease in humans, although C gattii may affect more ostensibly immunocompetent persons. It is a major cause of cryptococcosis in the Pacific northwestern region of the United States and may result in more severe disease than C neoformans.
Infections are acquired by inhalation. In the lung, the infection may remain localized, heal, or disseminate. Clinically apparent cryptococcal pneumonia rarely develops in immunocompetent persons. Progressive lung disease and dissemination most often occur in the setting of cellular immunodeficiency, including underlying hematologic malignancies under treatment, Hodgkin lymphoma, long-term corticosteroid therapy, solid-organ transplant, TNF-alpha inhibitor therapy, or HIV infection.
Pulmonary disease ranges from simple nodules to widespread infiltrates leading to respiratory failure. Disseminated disease may involve any organ, but CNS disease predominates. Headache is usually the first symptom of meningitis. Confusion and other mental status changes as well as cranial nerve abnormalities, nausea, and vomiting may be seen as the disease progresses. Nuchal rigidity and meningeal signs occur about 50% of the time but are uncommon in HIV-infected patients. Communicating hydrocephalus may complicate the course. C gattii infection frequently presents with respiratory symptoms along with neurologic signs caused by space-occupying lesions in the CNS. Primary C neoformans infection of the skin may mimic bacterial cellulitis, especially in persons receiving immunosuppressive therapy such as corticosteroids. Paradoxical clinical worsening associated with improved immunologic status has been reported in HIV-positive and transplant patients with cryptococcosis; this entity has been labeled the immune reconstitution inflammatory syndrome (IRIS).
Respiratory tract disease is diagnosed by culture of respiratory secretions or pleural fluid. For suspected meningeal disease, lumbar puncture is the preferred diagnostic procedure. Spinal fluid findings include increased opening pressure, variable pleocytosis, increased protein, and decreased glucose, though as many as 50% of AIDS patients have no pleocytosis. Gram stain of the CSF usually reveals budding, encapsulated fungi. Cryptococcal capsular antigen in CSF and culture together establish the diagnosis over 90% of the time. Patients with AIDS often have the antigen in both CSF and serum, and extrameningeal disease (lungs, blood, urinary tract) is common. In patients with AIDS, the serum cryptococcal antigen is also a sensitive screening test for meningitis, being positive in over 95% of cases. MRI is more sensitive than CT in finding CNS abnormalities such as cryptococcomas. ...