Tuberculous meningitis

What it is

Tuberculous meningitis is central nervous system disease due to TB. It is one of the causes of subacute or chronic meningitis, with neurobrucellosis and, in HIV with low CD4 counts, cryptococcal meningitis.

Causes and risk

It develops most commonly as a complication of progressive primary infection in infants and young children, and from chronic reactivation bacillemia in older adults with immune deficiency state. The noninfectious conditions that also give subacute or chronic meningitis are neoplastic disease, sarcoidosis, systemic lupus erythematosus, granulomatosis with polyangiitis (Wegener's), Behcet's disease, Fabry disease, central nervous system vasculitis, Vogt-Koyanagi-Harada disease, chemical or drug-induced meningitis, and idiopathic in up to one-third of cases. The drugs given are nonsteroidal anti-inflammatory drugs, intravenous immunoglobulin and intrathecal agents.

How it is diagnosed

Early recognition of tuberculous meningitis is of paramount importance. The laboratory findings in TB are normocytic, normochromic anemia, hypoalbuminemia and hypergammaglobulinemia, which are characteristic of advanced disease. The white blood cell count is usually normal, and monocytosis can be seen. Hypercalcemia is given, from activated macrophages in granulomas producing high calcitriol levels, and hyponatremia, from SIADH in the context of TB meningitis or pulmonary disease and from adrenal involvement. The fluid itself is worth holding in mind: CSF analysis shows high protein, low glucose and a lymphocytic pleocytosis of between 100 and 500 cells/microL. Evidence of concomitant extrameningeal tuberculosis is present in roughly three fourths of cases, so in most patients there is tuberculosis outside the meninges to be found. The course that brings it begins with a prodrome of malaise, intermittent headache and low-grade fever, followed within 2 to 3 weeks by protracted headache, vomiting, confusion, meningismus and focal neurologic signs, and CT or MRI may reveal basilar arachnoiditis, cerebral infarction or hydrocephalus.