Tuberculous meningitis
Overview
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 envelops the central nervous system. It is the most common form of CNS tuberculosis.
Symptoms
* Fever * Nausea And Vomiting * Loss of Appetite * Stiff Neck * Headache Severe * Coma * Seizures * Indifferent Mood * Light Hurts Eyes
Causes
Mycobacterium tuberculosis
Diagnosis
Diagnosis of TB meningitis is made by analysing CSF 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. 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. Nucleic acid amplification tests (NAAT) This is a heterogeneous group of tests that use polymerase chain reaction (PCR) to detect mycobacterial nucleic acid. These test vary in which nucleic acid sequence they detect and vary in their accuracy. The two most common commercially available tests are the amplified mycobacterium tuberculosis direct test (MTD, Gen-Probe) and Amplicor. In 2007, a systematic review of NAAT by the NHS Health Technology Assessment Programme concluded that for diagnosing tuberculous meningitis "Individually, the AMTD test appears to perform the best (sensitivity 74% and specificity 98%) [page 87]" [2]. In the NHS meta-analysis, they found the pooled prevalence of TB meningitis to be 29% [page 85]; however there was much heterogeneity in the reported sensitivities. Using a clinical calculator, these numbers yield a positive predictive value of 94% and a negative predictive value of 90%; however the 30% prevalence may be high due to referral bias. Alternate estimates of disease prevalence can be entered into the clinical calculator to refine the predictive values.These intcances vary from patient to patient according to their pathology. Imaging Imaging studies such as CT or MRI may show features strongly suggestive of TB meningitis, but cannot diagnose it.
Treatment
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. Treatment must be started as soon as there is a reasonable suspicion of the diagnosis. Treatment must not be delayed while waiting for confirmation of the diagnosis. Hydrocephalus occurs as a complication in about a third of patients with TB meningitis and will require a ventricular shunt.