Tuberculous meningitis
| Tuberculous meningitis | |
|---|---|
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| CT scan showing tuberculous meningitis | |
| Classification and external resources | |
| Specialty | neurology |
| ICD-10 | A17.0, G01 |
| ICD-9-CM | 013.0, 322.9 |
| MedlinePlus | 000650 |
| eMedicine | neuro/385 |
| MeSH | D014390 |
Tuberculous meningitis is also known as TB meningitis or tubercular meningitis. Tuberculous meningitis is Mycobacterium tuberculosis infection of the meninges—the system of membranes which envelop the central nervous system.
Fever and headache are the cardinal features, confusion is a late feature and coma bears a poor prognosis. Meningism is absent in a fifth of patients with TB meningitis. Patients may also have focal neurological deficits.
Mycobacterium tuberculosis of the meninges is the cardinal feature and the inflammation is concentrated towards the base of the brain. When the inflammation is in the brain stem subarachnoid area, cranial nerve roots may be affected. The symptoms will mimic those of space-occupying lesions.
Blood-borne spread certainly occurs, presumably by crossing the blood–brain barrier; but a proportion of patients may get TB meningitis from rupture of a cortical focus in the brain; an even smaller proportion get it from rupture of a bony focus in the spine.
The pathophysiology of tuberculous meningitis has bacilli root itself to the brain parenchyma, which causes the formation of small subpial focus. Then there is an increase in size of Rich focus until rupture. Tubercles rupture in subarachnoid area causes meningitis.
Diagnosis of TB meningitis is made by analysing cerebrospinal fluid collected by lumbar puncture. When collecting CSF for suspected TB meningitis, a minimum of 1ml of fluid should be taken (preferably 5 to 10ml). The CSF usually has a high protein, low glucose and a raised number of lymphocytes. Acid-fast bacilli are sometimes seen on a CSF smear, but more commonly, M. tuberculosis is grown in culture. A spiderweb clot in the collected CSF is characteristic of TB meningitis, but is a rare finding. ELISPOT testing is not useful for the diagnosis of acute TB meningitis and is often false negative, but may paradoxically become positive after treatment has started, which helps to confirm the diagnosis.
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