CNS tuberculosis

CNS tuberculosis

What are the epidemiology and pathogenesis of CNS tuberculosis? 

Incidence of tuberculosis (TB) remains highest in Southeast Asia, sub-Saharan Africa, and Eastern Europe.

The Centers for Disease Control (CDC) estimated the incidence of TB to be 3.0 per 100,000 in 2013.

Development of tuberculous meningitis is not limited to immunocompromised patients and may occur in up to 10% of untreated TB in the immunocompetent. 

Mycobacterium tuberculosis has no natural reservoir other than infected hosts. It is spread by aerosolized droplets that allow bacilli to colonize the alveoli before spreading hematogenously to numerous sites throughout the body, including the CNS.

Tubercles of mononuclear cells around a center of caseating necrosis form in secondary sites such as the brain, which then rupture, allowing spread throughout the CNS.

What are the typical symptoms of CNS tuberculosis? 

CNS tuberculosis may present as an acute meningitic syndrome with headache, altered mental status, increased intracranial pressure, meningismus, seizures, and focal neurologic symptoms.

How is it diagnosed?

What are the expected CSF findings in CNS tuberculosis? 

Patients will have an elevated opening pressure, increased white blood cell count with 10 to 500 cells/cc with lymphocytic predominance, increased protein of 100 to 500 mg/dL, and decreased glucose. Cultures are positive in 75% of cases and require 3 to 6 weeks of growth.

Subacutely, it may present as cranial nerve deficits due to coating of the nerves by exudate as a result of a hypersensitivity reaction to basilar meningitis.

Often, it may present chronically as a slowly progressive dementing illness with abulia and incontinence due to frontal lobe deficits.

What is the differential diagnosis of CNS tuberculosis? 

  • Fungal or partially treated bacterial meningitis as well as viral encephalitis can present with a similar CSF profile.
  • Noninfectious considerations include autoimmune encephalitis,
  • carcinomatous o lymphomatous meningitis,
  • neurosarcoidosis,
  • CNS sarcoidosis,
  • Behçet’s syndrome,
  • systemic lupus erythematosus,
  • Mollaret’s meningitis,
  • Wegener’s granulomatosis.

What are some common complications of CNS tuberculosis? 

Patients may commonly develop

  • communicating hydrocephalus,
  • infarctions due to vasculitis or direct invasion of blood vessel walls,
  • cranial nerve deficits,
  • seizures,
  • cognitive impairment,
  • myelitis,
  • radiculitis

What is the effect of coinfection with HIV on CNS tuberculosis? 

The clinical presentation of tuberculous meningitis is very similar in HIV and non-HIV-infected individuals, although HIV-infected patients are more likely to have mass lesions and extrameningeal TB at time of presentation. 

Sources

Centers for Disease Control and Prevention: Tuberculosis (TB). Available at http://www.cdc.gov/tb/statistics/reports/2013/table1.html 

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