Medicine – Reduced or Absent Glucose in CSF

Low cerebrospinal fluid (CSF) glucose, or hypoglycorrhachia, is an important clue in the investigation of meningitis and meningeal disease. CSF glucose should ideally be interpreted in relation to a simultaneous blood glucose, because the absolute CSF value alone can be misleading.

A reduced CSF glucose level is especially associated with bacterial meningitis, tuberculous meningitis, fungal meningitis, and malignant infiltration of the meninges.

1. Bacterial Meningitis

Acute bacterial meningitis is one of the classic causes of markedly reduced CSF glucose.

The typical CSF pattern is:

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

The low glucose results from a combination of increased glucose consumption by inflammatory cells and microorganisms, together with impaired transport of glucose across the inflamed blood-CSF barrier.

2. Tuberculous Meningitis

Tuberculous meningitis also classically produces low CSF glucose.

The characteristic pattern is:

Lymphocytes ↑ + protein ↑↑↑ + glucose ↓↓.

This can help distinguish TB meningitis from typical viral meningitis, where CSF glucose is usually normal.

Therefore:

Lymphocytes + low glucose → think TB or fungal meningitis rather than uncomplicated viral meningitis.

3. Malignant Meningitis

Malignant meningitis, also called leptomeningeal carcinomatosis or leptomeningeal metastasis, can produce reduced CSF glucose.

This occurs when malignant cells infiltrate the leptomeninges and interfere with normal CSF metabolism and transport.

Associated findings may include:

Raised CSF protein.

Increased opening pressure.

Abnormal CSF cytology.

Variable white-cell elevation.

Diagnosis often relies on CSF cytology and contrast-enhanced MRI, sometimes requiring repeated CSF sampling.

4. Fungal Meningitis

Fungal meningitis is another important cause of low CSF glucose.

The CSF often resembles TB meningitis:

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

A particularly important example is cryptococcal meningitis, especially in immunocompromised patients.

Opening pressure may also be markedly elevated in cryptococcal meningitis.

5. Mumps Meningitis

The original notes list mumps as an atypical cause.

Mumps can cause viral meningitis, but this needs qualification.

Most viral meningitides have a normal CSF glucose, and mumps is one of the viral infections in which CSF glucose can occasionally be reduced.

Therefore, mumps should be remembered as an exception rather than a typical cause of severe hypoglycorrhachia.

6. Other Causes

Other conditions can also lower CSF glucose.

These include some chronic infections, certain inflammatory meningeal diseases, and occasionally severe neurosarcoidosis.

However, the major examination causes remain:

Bacterial meningitis.

TB meningitis.

Fungal meningitis.

Malignant meningitis.

7. CSF-to-Blood Glucose Ratio

The CSF glucose value is best interpreted alongside plasma glucose.

Normally:

CSF glucose ≈ 60–70% of plasma glucose.

A reduced CSF:plasma glucose ratio, particularly below about 0.4, supports pathological hypoglycorrhachia in the appropriate clinical setting.

8. Reduced CSF Glucose – Note Form

Bacterial meningitis: low glucose + neutrophils + high protein.

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

Fungal meningitis: low glucose + lymphocytic/mononuclear response + high protein.

Malignant meningitis: low glucose + high protein ± malignant cells in CSF.

Mumps meningitis: viral meningitis usually has normal glucose, but mumps can occasionally lower it.

Key Clinical Pattern

Remember:

Low CSF glucose → bacterial, TB, fungal, or malignant meningitis.

A useful distinction is:

Neutrophils + low glucose → bacterial meningitis.

Lymphocytes + low glucose → TB or fungal meningitis.

Lymphocytes + normal glucose → typical viral meningitis.

Low glucose + malignant cells → leptomeningeal malignancy.