Makindo Medical Notes

Related Subjects: |Lumbar Puncture |CSF Interpretation |CSF Rhinorrhoea

🧠 Cerebrospinal Fluid (CSF) Interpretation is one of the most powerful diagnostic tools in neurology and acute medicine. When interpreted correctly, CSF can rapidly distinguish infection, inflammation, malignancy, haemorrhage, and demyelination. The key is pattern recognition — never interpret a single value in isolation.

🔬 What is CSF and Why It Matters

CSF is a clear, colourless fluid produced by the choroid plexus that cushions the brain and spinal cord, delivers nutrients, and removes waste. Abnormalities reflect disruption of the blood–brain barrier, inflammation, infection, haemorrhage, or impaired CSF flow. Because CSF and serum exist in dynamic equilibrium, paired CSF and serum samples are essential for accurate interpretation.

📊 Normal CSF Values (Adults)

• Opening pressure: 7–20 cm H₂O
• WCC: <5 cells/μL (mostly lymphocytes)
• Protein: <0.4 g/L
• Glucose: 2.5–3.5 mmol/L (CSF:serum ratio ≥0.5)
• Lactate: 1–2 mmol/L

⬆️ Causes of Increased CSF Protein

Raised CSF protein reflects increased permeability, intrathecal protein production, or impaired CSF circulation. The white cell count and glucose usually point you toward the underlying pathology.

• Guillain–Barré syndrome ⚡ – high protein with normal WCC (albuminocytologic dissociation).
• Bacterial meningitis – neutrophils + high protein.
• Tuberculous meningitis – lymphocytes + very high protein.
• Fungal meningitis – lymphocytes + raised protein.
• Multiple sclerosis – selective IgG elevation.
• Neurosyphilis, sarcoidosis, vasculitis.
• Subdural haematoma, malignancy.
• Froin’s syndrome 🚧 – CSF flow obstruction → very high protein, xanthochromia.

🧬 Oligoclonal IgG Bands

Oligoclonal bands indicate intrathecal IgG synthesis. They support inflammatory CNS disease but are not disease-specific.

• Multiple sclerosis ⭐
• Neurosarcoidosis
• Systemic lupus erythematosus
• Neurosyphilis
• Behçet’s disease
• Subacute sclerosing panencephalitis (post-measles)

⬇️ Low CSF Glucose

Low glucose suggests high metabolic activity from organisms or inflammatory cells, or impaired glucose transport. Always calculate the CSF:serum glucose ratio.

• Bacterial meningitis 🦠
• Tuberculous meningitis
• Fungal meningitis
• Sarcoidosis
• Leptomeningeal malignancy
• Subarachnoid haemorrhage

🧪 CSF Cell Patterns

• Neutrophils: Bacterial meningitis, early TB.
• Lymphocytes: Viral, TB, fungal, inflammatory, malignancy.
• Eosinophils: Parasites, drugs, shunts.

🩸 Bloody Tap vs Subarachnoid Haemorrhage

🧠 Bloody tap rule: subtract 1 WCC per 1000 RBCs to estimate true CSF WCC.
🔑 Xanthochromia and persistent RBCs across tubes suggest true SAH, not traumatic tap.

📊 Classic CSF Patterns

🩺 Clinical Cases

Case 1 – Fever and Confusion 🦠
A 67-year-old man presents with fever, neck stiffness, and reduced GCS. CSF shows neutrophils 12,000/mm³, protein 2.5 g/L, glucose 1.2 mmol/L. → Bacterial meningitis. Treat immediately — do not wait for cultures.

Case 2 – Headache After a Viral Prodrome 🤧
A 22-year-old woman presents with headache and photophobia. CSF shows lymphocytes 120/mm³, normal glucose, mildly raised protein. → Viral meningitis. Supportive management.

Case 3 – Progressive Cranial Neuropathies 🧠
A 54-year-old man with weight loss and night sweats. CSF: lymphocytes, protein 3.0 g/L, glucose low. → Tuberculous meningitis. Start treatment early.

Case 4 – Ascending Weakness ⚡
A 40-year-old man develops ascending paralysis post-GI infection. CSF: protein 1.8 g/L, WCC 1/mm³. → Guillain–Barré syndrome (albuminocytologic dissociation).

Case 5 – Young Adult with Optic Neuritis 👁️
A 29-year-old woman with optic neuritis and sensory symptoms. CSF: oligoclonal bands present, normal glucose and cells. → Multiple sclerosis.

📌 Take-Home Messages

• Interpret CSF as a pattern, not isolated numbers.
• Always pair CSF with serum glucose.
• Low glucose + high protein = infection or malignancy until proven otherwise.
• High protein + normal cells = think GBS.
• CSF interpretation saves lives when done early and correctly.