neurologic disorders
Subacute and Chronic Meningitis
Diagnosis of Subacute and Chronic Meningitis
CSF analysis Clinical findings in patients with subacute or chronic meningitis are often nonspecific. However, a careful search for a systemic infection or disorder may suggest a cause for meningitis. Also, sometimes risk factors (eg, immunocompromise, HIV infection or risk factors for it, recent time spent in endemic areas) and occasionally specific neurologic deficits (eg, particular cranial nerve deficits) suggest specific causes, such asC. neoformansmeningitis in HIV-infected patients orC. immitisinfections in patients living in the southwestern US. Typically, CSF findings include lymphocytic pleocytosis. In many of the infections that cause chronic meningitis, CSF contains only a few of the organisms, making identification of the cause difficult. Thus, diagnosis of subacute or chronic meningitis based on CSF findings may require multiple large samples over time, particularly for cultures. CSF analysis commonly includes Aerobic and anaerobic bacterial culture Mycobacterial and fungal culture Cryptococcal antigen testing Antigen or serologic testing Special stains (eg, acid-fast staining, India ink) Cytology If available, next-generation (metagenomic) sequencing can be used to rapidly sequence large stretches of nucleic acids and thus identify otherwise undetectable pathogens in CSF. If clinicians suspect tuberculous meningitis, they can use an automated test called Xpert MTB/RIF, which has been recommended by the WHO for the diagnosis of tuberculous meningitis. This test can detect the DNA ofMycobacterium tuberculosisin CSF specimens. Skin testing with controls for anergy or QuantiFERON®-TB Gold testing can document prior exposure toM. tuberculosis; however, results may be negative, particularly in older or immunosuppressed patients. Chest x-rays may show evidence of prior or ongoing infection (eg, in 40 to 50% of cases), and chest CT is positive in up to two thirds of cases. If CSF findings do not provide a diagnosis and meningitis is causing morbidity or is progressive, more invasive testing (eg, cisternal or ventricular puncture, biopsy) is indicated. Occasionally, organisms are recovered from ventricular or cisternal CSF when lumbar CSF is negative. MRI or CT may be done to identify focal areas of inflammation for biopsy; blind meningeal biopsy has a very low yield. 