Cerebrospinal Fluid (CSF) Analysis

•    Bacterial meningitis:

o    Appearance: cloudy/turbid.

o    Cells: high neutrophils (polymorphs).

o    Protein: elevated (>1 g/L).

o    Glucose: low (<50% of plasma glucose).

o    Opening pressure: often high.

•    Viral meningitis:

o    Appearance: clear.

o    Cells: lymphocytic predominance.

o    Protein: mildly elevated or normal.

o    Glucose: normal.

•    Tuberculous meningitis:

o    Lymphocytes, very high protein, very low glucose.

o    "Cobweb" formation on standing.

•    Fungal (e.g., cryptococcus):

o    Common in immunosuppressed.

o    Lymphocytes, low glucose, high opening pressure.

•    Multiple sclerosis:

o    Oligoclonal bands: present in CSF but absent in serum (indicates intrathecal synthesis).

•    Subarachnoid haemorrhage:

o    Xanthochromia (bilirubin breakdown product), persists >12 hours.

Neuroimaging

•    CT head:

o    Indications: acute stroke (to exclude bleed), head trauma, hydrocephalus.

o    Early detection of haemorrhage (hyperdense), late detection of infarct (hypodense).

o    Better for bone detail.

•    MRI brain:

o    Demyelinating lesions (MS plaques), tumours, posterior fossa structures, encephalitis (temporal lobes in HSV).

o    DWI sequence for early ischaemia.

•    MR angiography/CT angiography:

o    Vessel occlusion or aneurysms (e.g., SAH work-up).

Electrophysiological Studies

•    Nerve Conduction Studies (NCS):

o    Differentiate axonal loss (reduced amplitude) vs demyelination (slowed conduction velocity, prolonged distal latencies).

•    Electromyography (EMG):

o    Muscle diseases (myopathic changes: small, polyphasic units).

o    Neurogenic changes: large, polyphasic units with reduced recruitment.

•    Repetitive nerve stimulation:

o    MG: decremental response.

o    LEMS: incremental response with high-frequency stimulation.

•    Single-fibre EMG:

o    Most sensitive for MG.

Electroencephalography (EEG)

•    Used for:

o    Epilepsy diagnosis (generalised spike-wave discharges in absence seizures).

o    Encephalopathies (triphasic waves in metabolic encephalopathy).

o    Brain death assessment (absence of activity).

Evoked Potentials

•    Visual Evoked Potentials (VEP):

o    Delayed P100 latency → optic neuritis (early demyelination marker).

•    Somatosensory Evoked Potentials (SSEP):

o    Assess dorsal column function; useful in MS and spinal cord disease.

•    Brainstem Auditory Evoked Potentials (BAEP):

o    Diagnose acoustic neuromas, brainstem lesions.

Extra Revision Pearls

•    Always check for raised ICP before LP → risk of coning.

•    MRI is superior for posterior fossa and spinal cord.

•    Oligoclonal bands in CSF but not serum = strong clue for MS.

•    EMG/NCS patterns help differentiate neuropathy (length-dependent, "glove and stocking") vs myopathy (proximal weakness).

•    EEG can be normal between seizures → does not exclude epilepsy.