Chronic bacterial meningoencephalitis: TB, syphilis, Lyme
- Lesion
Tuberculosis, syphilis and Lyme disease can smoulder in the brain for weeks or years, causing chronic meningitis, strokes and dementia.
What it is
Some bacteria cause slow, granulomatous or chronic inflammation of the meninges and brain. Tuberculous meningitis forms a thick gelatinous exudate at the base of the brain that strangles arteries and blocks CSF flow; a tuberculoma is a caseating mass. Neurosyphilis, in the tertiary stage, affects meningeal vessels, the cortex (general paresis) or the dorsal columns (tabes dorsalis). Lyme neuroborreliosis gives lymphocytic meningitis and cranial nerve palsies, typically of the facial nerve.
Structure
- TB meningitis gross: grey gelatinous exudate filling the basal cisterns, around the circle of Willis and cranial nerves.
- Neurosyphilis can also give gummas, rare necrotic granulomatous masses; congenital syphilis can involve the CNS.
- In HIV, neurosyphilis and tuberculous meningitis are more frequent and more aggressive.
Chronic bacterial infections of the CNS
| Disease | Main lesion | Key microscopy | Typical consequence |
|---|---|---|---|
| Tuberculous meningitis | Basal gelatinous exudate | Caseating granulomas, endarteritis | Infarcts, hydrocephalus, cranial nerve palsies |
| Tuberculoma | Intraparenchymal mass | Caseation with epithelioid histiocytes and giant cells | Seizures, mass effect |
| Meningovascular neurosyphilis | Thickened meninges and arteries | Plasma cells, obliterative endarteritis | Strokes |
| General paresis | Cortical atrophy, frontal | Spirochetes, rod microglia, iron | Dementia, psychosis |
| Tabes dorsalis | Dorsal roots and columns | Axon and myelin loss | Sensory ataxia, lightning pains |
| Lyme neuroborreliosis | Meninges, cranial nerves, roots | Lymphocytes and plasma cells | Facial palsy, radiculitis |
Clinical notes
- Tuberculous meningitis develops over weeks with headache, confusion, cranial nerve palsies and fever; delayed diagnosis leaves severe sequelae.
- Argyll Robertson pupils: small pupils that accommodate but do not react to light, classic of tabes.
Test yourself
Think of the answer, then tap the question to see it.
Why does tuberculous meningitis cause infarcts?
The basal exudate causes obliterative endarteritis of arteries crossing the subarachnoid space, which narrows and occludes them.
Which part of the spinal cord is lost in tabes dorsalis?
The dorsal roots and dorsal columns, so position and vibration sense are lost and gait becomes ataxic.
Which cranial nerve is classically affected by Lyme neuroborreliosis?
The facial nerve, sometimes on both sides.
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Meningitis - tuberculous: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Neurosyphilis: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026).
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Representative model, for educational purposes only.