Medicine – Cells in Cerebrospinal Fluid (CSF)

The type of white blood cell present in cerebrospinal fluid provides an important clue to the underlying neurological disorder. The most useful distinction is between neutrophilic (polymorph) predominance and lymphocytic predominance.

However, cell patterns are not completely specific and can change with the stage of illness, prior antibiotic treatment, and underlying immune status.

1. Polymorphs in CSF

Polymorphs, meaning mainly neutrophils, are classically associated with acute bacterial meningitis.

The usual pattern is:

Neutrophils ↑↑ + protein ↑↑ + glucose ↓↓.

Bacterial Meningitis

In acute bacterial meningitis, the meninges become intensely inflamed and large numbers of neutrophils migrate into the CSF.

The cell count may rise into the hundreds or thousands per microlitre.

Common associated findings include:

Raised opening pressure.

Turbid CSF.

Low CSF glucose.

Markedly raised protein.

Important Exception

Neutrophils are not exclusive to bacterial meningitis.

Early viral meningitis, particularly during the first hours of illness, may sometimes show a temporary neutrophilic predominance before becoming lymphocyte-predominant.

Therefore, the full CSF pattern and clinical context must be considered.

2. Lymphocytes in CSF

A lymphocytic or mononuclear predominance is classically associated with viral, chronic infectious, inflammatory, malignant, or immune-mediated CNS disorders.

The major causes from your notes include:

Viral meningitis or encephalitis.

Partially treated bacterial meningitis.

CNS vasculitis.

HIV-associated neurological disease.

Leukaemia.

3. Viral Meningitis

Typical viral meningitis produces a lymphocytic pleocytosis.

The usual pattern is:

Lymphocytes ↑ + protein mildly/moderately ↑ + glucose usually normal.

Patients often present with headache, fever, photophobia, neck stiffness, and relatively preserved consciousness compared with severe bacterial meningitis.

4. Viral Encephalitis

Viral encephalitis also usually produces a lymphocyte-predominant CSF response.

However, because encephalitis involves the brain parenchyma rather than only the meninges, patients are more likely to have:

Altered consciousness.

Confusion or behavioural change.

Seizures.

Focal neurological deficits.

HSV Encephalitis

Herpes simplex virus encephalitis is an especially important cause.

CSF typically shows:

Lymphocytic pleocytosis.

Raised protein.

Usually normal glucose.

Red blood cells may sometimes be present because HSV encephalitis can cause haemorrhagic necrosis, particularly in the temporal lobes.

Diagnosis is usually supported by CSF HSV PCR.

5. Partially Treated Bacterial Meningitis

Bacterial meningitis that has already received antibiotics may show an altered CSF pattern.

The cell differential can become less typically neutrophilic and may become relatively lymphocyte-predominant.

Therefore:

Lymphocytes in CSF do not completely exclude bacterial meningitis, especially after prior antibiotic therapy.

Other findings such as low glucose and high protein may still support bacterial infection.

6. Tuberculous Meningitis

Although not listed in your current note, TB meningitis is one of the most important causes of lymphocytic CSF.

The classic pattern is:

Lymphocytes ↑ + protein ↑↑↑ + glucose ↓↓ + opening pressure ↑.

This is a high-yield distinction from uncomplicated viral meningitis.

7. Fungal Meningitis

Chronic fungal meningitis, including cryptococcal meningitis, also commonly causes a mononuclear or lymphocytic CSF pattern.

The typical combination is:

Lymphocytes/mononuclear cells ↑ + protein ↑ + glucose ↓.

This can closely resemble TB meningitis.

8. CNS Vasculitis

Central nervous system vasculitis may cause a mild inflammatory CSF picture.

CSF may show:

Lymphocytic pleocytosis.

Raised protein.

Glucose is usually relatively preserved.

These findings are nonspecific, so diagnosis depends on the broader clinical picture, imaging, laboratory tests, and occasionally vascular imaging or biopsy.

9. HIV-Associated Disease

Patients with HIV infection can develop a variety of CNS disorders associated with lymphocytes in the CSF.

This may occur with HIV itself or with opportunistic infections.

Examples include:

HIV-associated aseptic meningitis.

Cryptococcal meningitis.

Tuberculous meningitis.

Viral CNS infections.

Therefore, in an immunocompromised patient, CSF findings must be interpreted cautiously because inflammatory cell responses may sometimes be relatively modest despite severe infection.

10. Leukaemia

Leukaemia can involve the meninges and central nervous system.

Malignant cells may enter the CSF, producing leptomeningeal leukaemic involvement.

The CSF may contain increased mononuclear cells, but the key diagnostic issue is identifying abnormal malignant cells, rather than simply calling the response lymphocytic.

11. CSF Cytology

When malignant CNS involvement is suspected, CSF cytology is important.

Flow cytometry can also be especially valuable for detecting haematological malignancy involving the CSF.

In some cases, repeated lumbar punctures may be needed because malignant cells may not be detected in the first sample.

12. Other Causes of Lymphocytic CSF

Other important causes include:

Multiple sclerosis, which may produce a mild lymphocytic pleocytosis.

Neurosarcoidosis.

Syphilitic meningitis.

Lyme neuroborreliosis.

Autoimmune encephalitis.

These conditions generally produce much lower cell counts than acute bacterial meningitis.

13. Polymorphs – Note Form

Main association: acute bacterial meningitis.

Typical accompanying findings: low glucose + very high protein + raised opening pressure.

Important exception: early viral meningitis can temporarily show neutrophils.

14. Lymphocytes – Note Form

Viral meningitis: lymphocytes + normal glucose + moderately raised protein.

Viral encephalitis: lymphocytes + raised protein, usually normal glucose.

Partially treated bacterial meningitis: may become lymphocyte-predominant.

TB meningitis: lymphocytes + low glucose + very high protein.

Fungal meningitis: lymphocytes/mononuclear cells + low glucose + high protein.

CNS vasculitis: mild lymphocytic pleocytosis + raised protein.

HIV-associated CNS disease: often mononuclear/lymphocytic, but pattern depends on the underlying infection or process.

Leukaemia: malignant mononuclear cells may be present; confirm with cytology/flow cytometry.

Key Clinical Pattern

Remember:

Polymorphs/neutrophils → think bacterial meningitis.

Lymphocytes → think viral, TB, fungal, inflammatory, or malignant disease.

The fastest examination distinction is:

Neutrophils + low glucose → bacterial meningitis.

Lymphocytes + normal glucose → viral meningitis.

Lymphocytes + low glucose → TB or fungal meningitis.

Abnormal malignant cells → leukaemia or leptomeningeal malignancy.