The electrolytes should be tested to look for low sodium caused by SIADH which would favour a diagnosis of tuberculous meningitis.
A full blood count may help distinguish AIDS from leukaemia/lymphoma.
The brain should be imaged before a lumbar puncture is performed.
The lumbar puncture is often diagnostic in cases of fungal meningitis:
- pleocytosis is variable:
- usually less than 15 cell/mm^3
- initially excess polymorphonuclear cells but this changes to lymphocytes with time
- patients with AIDS may not have a pleocytosis
- protein is raised
- glucose is usually reduced
- India ink staining is positive
- cryptococcal antigen tests are sensitive
Last reviewed 01/2018