Tuberculous Meningitis – Diagnosis and Treatment
The causative agent is Mycobacterium tuberculosis, the bacteria that causes tuberculosis.
Tuberculous meningitis is usually secondary to Tuberculosis in some other part of the body. Most commonly, pulmonary tuberculosis, when left unchecked, becomes miliary and spreads to other parts of the body. The spread to the brain is usually via blood stream.
Meninges are the system of membranes which envelops the central nervous system. Blood infected with this bacteria moves all around the body. As it comes in touch with the meninges, they get infected.
Risk factors include a history of:
- Excessive alcohol use
- Pulmonary tuberculosis
- Weakened immune system
The symptoms usually begin gradually, and may include:
- Fever and chills
- Mental status changes
- Nausea and vomiting
- Sensitivity to light (photophobia)
- Severe headache
- Stiff neck (meningismus)
- Bulging fontanelles
- Decreased consciousness
- Poor feeding or irritability in children
- Unusual posture, with the head and neck arched backwards (opisthotonos)
Fever and headache are the cardinal features. Confusion is a late feature. The patient may even go into coma, which bears a poor prognosis. Patients may also have focal neurological deficits.
Diagnosis of TB meningitis is made by analyzing cerebrospinal fluid collected by lumbar puncture. 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.
More than half of cases of TB meningitis cannot be confirmed microbiologically, and these patients are treated on the basis of clinical suspicion only. The culture of TB from CSF takes a minimum of two weeks, and therefore the majority of patients with TB meningitis are started on treatment before the diagnosis is confirmed.
Imaging studies such as CT or MRI may show features strongly suggestive of TB meningitis, but cannot diagnose it.
The treatment of TB meningitis is isoniazid, rifampicin, pyrazinamide and ethambutol for two months, followed by isoniazid and rifampicin alone for a further ten months. Steroids are always used in the first six weeks of treatment (and sometimes for longer). A few patients may require immunomodulatory agents such as thalidomide.
Complications of Tuberculous Meningitis
- Brain damage
- Build-up of fluid between the skull and brain (subdural effusion)
- Hearing loss
- Hydrocephalus: This requires a ventricular shunt as treatment.