Meningitis

•    Clinical presentation:

o    Rapid onset headache, fever, neck stiffness, photophobia, vomiting.

o    Possible petechial rash (meningococcal).

o    Kernig’s & Brudzinski’s signs.

•    Aetiology:

o    Bacterial (common):

    Adults: Neisseria meningitidis, Streptococcus pneumoniae.

    Elderly/alcoholics: Listeria monocytogenes.

    Post-neurosurgery/trauma: Staph aureus, Gram-negatives.

o    Viral (aseptic): enteroviruses (most common), HSV-2, VZV.

•    CSF findings (bacterial):

o    ↓ Glucose (<50% of serum).

o    ↑ Protein.

o    ↑ Neutrophils.

o    ↑ Opening pressure.

•    Initial management:

o    Empirical Abx: IV ceftriaxone ± ampicillin (for Listeria cover in elderly or immunocompromised).

o    Dexamethasone if pneumococcal suspected (reduces hearing loss, mortality).

•    Contraindications to immediate LP:

o    GCS <12, focal neurology, papilloedema, recent seizures → do urgent CT first.

Encephalitis

•    Clinical features:

o    Altered mental status, confusion, behavioural changes, seizures.

o    ± fever, focal signs.

•    Common causes:

o    HSV-1: most common sporadic encephalitis in adults; temporal lobe involvement.

o    VZV, EBV, CMV (immunocompromised).

•    Diagnosis:

o    CSF: lymphocytic pleocytosis, normal/↑ protein, normal glucose.

o    PCR: HSV DNA.

•    MRI:

o    Temporal lobe hyperintensities.

•    Management:

o    IV aciclovir ASAP (do not delay for PCR results).

Lyme Disease (Neuroborreliosis)

•    Features:

o    Early disseminated phase: facial nerve palsy (often bilateral), radiculopathy, lymphocytic meningitis.

•    Diagnosis:

o    Serum ELISA → confirm with Western blot.

•    Treatment:

o    IV ceftriaxone (for neuro involvement).

Prion Diseases

•    Features:

o    Rapidly progressive dementia, myoclonus, ataxia.

o    Startle-induced myoclonus characteristic.

•    Investigations:

o    MRI: pulvinar sign ("hockey stick sign") in variant CJD.

o    EEG: periodic sharp wave complexes (sporadic CJD).

o    CSF: 14-3-3 protein (supportive, not definitive).

•    Prognosis:

o    Rapidly fatal; no effective treatment.

HIV-Related CNS Infections

Progressive Multifocal Leukoencephalopathy (PML)

•    Cause:

o    JC virus reactivation in severe immunosuppression (CD4 <100).

•    Features:

o    Subacute neurological deficits (weakness, speech, vision).

o    No mass effect or enhancement.

•    MRI:

o    Multifocal white matter lesions, no contrast enhancement.

CNS Toxoplasmosis

•    Features:

o    Headache, confusion, focal deficits, fever.

o    Common with CD4 <100, especially if not on prophylaxis.

•    Imaging:

o    Multiple ring-enhancing lesions (basal ganglia, corticomedullary junction).

•    Treatment:

o    Pyrimethamine, sulfadiazine, leucovorin.

o    Empirical treatment often started if imaging suggests.

Extra Revision Pearls

•    Rash with meningitis → think meningococcal septicaemia (urgent Abx even before LP).

•    Empirical meningitis Abx always include Listeria cover (>60, immunocompromised, pregnancy).

•    HSV encephalitis clue → temporal lobe (olfactory/gustatory hallucinations, personality change).

•    Bilateral CN VII palsy → classic clue for Lyme neuroborreliosis.

•    HIV CNS lesions → toxoplasmosis (multiple rings) vs lymphoma (usually solitary).

•    Avoid LP in suspected raised ICP → risk of herniation.