Differential Diagnosis for CSF Findings

The patient's cerebrospinal fluid (CSF) analysis shows 5 cells, all of which are lymphocytes, low glucose, elevated proteins, and a negative adenosine deaminase (ADA) test. Here's a structured approach to the differential diagnosis:

• Single Most Likely Diagnosis

  • Tuberculous Meningitis (TBM): Although the ADA test is negative, which is often used to support the diagnosis of TBM, the combination of low glucose, elevated proteins, and lymphocytic pleocytosis in the CSF is highly suggestive of TBM, especially in endemic areas or in patients with risk factors. A negative ADA does not rule out TBM, as its sensitivity is not 100%.

• Other Likely Diagnoses

  • Viral Meningitis: The presence of lymphocytic pleocytosis is consistent with viral meningitis. However, viral meningitis typically has a higher glucose level in the CSF and lower protein levels compared to what is described.
  • Fungal Meningitis: This condition, such as cryptococcal meningitis, can present with low glucose and elevated protein in the CSF, along with lymphocytic pleocytosis. It is more common in immunocompromised patients.
  • Lymphomatous Meningitis: Involvement of the CNS by lymphoma can cause these CSF findings, particularly in patients with a known history of lymphoma.

• Do Not Miss Diagnoses

  • Subarachnoid Hemorrhage: Although the cell count is low, and all cells are lymphocytes, it's crucial to consider subarachnoid hemorrhage, especially if there's a history suggestive of a hemorrhagic event. The xanthochromia (yellow discoloration of the CSF due to bilirubin) would be a key differentiator but may not be present early on.
  • Bacterial Meningitis (Partially Treated): If a patient has been partially treated with antibiotics, the CSF findings can be atypical, with lower cell counts and a mixed or lymphocytic predominance. It's essential to consider this diagnosis due to its high morbidity and mortality if not promptly treated.
  • Neurosarcoidosis: This condition can cause a wide range of CSF abnormalities, including low glucose and elevated protein, along with lymphocytic pleocytosis. It's a diagnosis of exclusion but should be considered, especially in patients with systemic symptoms of sarcoidosis.

• Rare Diagnoses

  • Leptin Meningitis: A rare cause of meningitis that can present with similar CSF findings.
  • CNS Histoplasmosis: In endemic areas, Histoplasma capsulatum can cause CNS infection, presenting with low glucose, elevated protein, and lymphocytic pleocytosis in the CSF.
  • CNS Coccidioidomycosis: Similar to histoplasmosis, coccidioidomycosis can cause meningitis with these CSF findings, particularly in immunocompromised patients or those from endemic areas.

Each of these diagnoses requires careful consideration of the patient's clinical presentation, epidemiological history, and additional diagnostic tests to confirm the diagnosis.