MI6.1-3 | Central Nervous System Infections — Glossary

An enzyme elevated in the CSF of patients with TBM (typically >10 IU/L); a useful ancillary test when GeneXpert and ZN stain are negative but TBM is clinically suspected.

Meningitis with no bacterial growth on standard culture media; includes viral, fungal, tuberculous, drug-induced, and parameningeal causes — not synonymous with mild or self-limiting disease.

A selective barrier formed by tight junctions between cerebral capillary endothelial cells, astrocytes, and pericytes that restricts passage of large molecules, many drugs, and most microorganisms from blood into brain tissue.

A clinical sign of meningeal irritation: passive flexion of the neck causes involuntary flexion of the hips and knees; positive in meningitis.

A severe complication of Plasmodium falciparum malaria caused by sequestration of parasitised RBCs in cerebral capillaries, leading to impaired microcirculation, coma, and seizures; not a true meningitis or encephalitis by mechanism.

A highly sensitive and specific serological test detecting capsular polysaccharide antigen of Cryptococcus neoformans in CSF or serum; detected by latex agglutination or lateral flow assay; preferred over India ink for diagnosis.

Inflammation of the brain parenchyma, causing altered consciousness, behavioural change, seizures, and focal neurological deficits; often accompanied by meningeal inflammation (meningoencephalitis).

A real-time PCR-based cartridge assay for Mycobacterium tuberculosis detection and rifampicin resistance assessment in CSF; WHO-recommended first-line test for TBM diagnosis.

A negative contrast technique where India ink particles are excluded from the polysaccharide capsule of Cryptococcus neoformans, producing a clear halo around the yeast cells against a dark background; used to detect cryptococcal meningitis in CSF.

A flavivirus transmitted by Culex mosquitoes causing acute encephalitis in India, particularly in UP, Bihar, and Assam during monsoon season; diagnosed by JEV IgM MAC-ELISA in CSF or serum.

A clinical sign of meningeal irritation: with the hip flexed 90°, the knee cannot be fully extended past 135° due to hamstring spasm; positive in meningitis.

IgM antibody capture enzyme-linked immunosorbent assay; the standard serological test for Japanese encephalitis virus IgM detection in CSF or serum; positive result in the appropriate clinical context is diagnostic.

Inflammation of the meninges (dura, arachnoid, pia mater) and the subarachnoid space; characterised by fever, headache, neck stiffness, photophobia, and CSF pleocytosis.

Intracytoplasmic eosinophilic inclusion bodies in Purkinje and pyramidal neurons, pathognomonic of rabies virus infection; detected on brain biopsy (or post-mortem) using haematoxylin and eosin stain.

An abnormal increase in white blood cell count in the CSF; neutrophilic pleocytosis suggests bacterial aetiology; lymphocytic pleocytosis suggests viral, fungal, or tuberculous aetiology.

A rapidly fatal meningoencephalitis caused by Naegleria fowleri, a free-living amoeba acquired from warm freshwater; amoebic trophozoites are identified on CSF wet mount.

Meningitis caused by Mycobacterium tuberculosis; characterised by subacute onset, basal exudate causing cranial nerve palsies, and CSF showing lymphocytic pleocytosis with very low glucose; diagnosed by GeneXpert Ultra and culture.

Yellow discolouration of the CSF caused by bilirubin from haemolysed red blood cells (subarachnoid haemorrhage), jaundice, or very high protein content; also seen in established TBM.