investigations

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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

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