Tuberculous Meningitis

INTRODUCTION:
  • Tuberculous meningitis is Mycobacterium tuberculosis infection of the meninges—the system of membranes which envelop the central nervous system.
  • In tuberculous meningitis, the greatest degree of meningeal involvement and collection of exudates is around the brainstem and at the base of the brain. 
SIGNS & SYMPTOMS:
  • Fever and chronic headache are the cardinal features,
  • Loss of appetite ,cough followed by neck rigidity
  • Raised intracranial tension in the form of vomiting and altered sensoriurn
  • Confusion is a late feature and 
  • Coma bears 
  • Meningism is absent in a fifth of patients with TB meningitis.
  • Patients may also have focal neurological deficits.
  • Complications of TB meningitis
  1. Hemiplegia (20%), quadriplegia (19%), monoplegia (3%) 
  2. Cranial nerve palsies (14%)
  3. Cerebral infarction
  4. Ptosis
  5. Hemiballismus (11%) 
  6. Decerebrate Rigidity (3%)
  7. Tremors (6.1%) 
  8. Decorticate Rigidity (3%)
  9. Midline cerebellar syndromes (4%) 
  10. Cerebellar Hemispheric Lesions (1.0%)
PATHOPHYSIOLOGY:
  • 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:
  • 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. 
  • CT scan may reveals Exudates seen in basal cistern and hydrocephalus
  • 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.
Nucleic acid amplification tests (NAAT)
  • This is a 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.
FEATURES Normal CSF findings Tuberculous CSF finding
Gross appearance Clear Clear or opaque
Pressure(cm H2O) 10-20 cm H 2 O Elevated
Glucose >60% of serum glucose Decreased
Protein < 45 mg/dL Increased
Chloride (116-122 mg/dl) Decrease
Cells <5/u ; Pleocytosis (lymphocytosisbutinitially neutrophilia may be seen)C.S.F. cell count varies between 100-1000
Exam Question
  • Loss of appetite cough followed by neck rigidity with increased protein level of CSF than normal & lymphocytosis is suggestive of TB meningitis.
  • Chronic headaches accompanied by chronic mild nuchal rigidity with Cerebrospinal fluid sampling showing a chronic inflammatory infiltrate with lymphocytes, plasma cells, macrophages, and fibroblasts is suggestive of Mycobacterium Tuberculosis infection
  • Raised intracranial tension in the form of vomiting and altered sensoriurn & CT scan showing basal exudates and hydrocephalus is suggestive of TB meningitis
  • CSF findings in tubercular meningitis includes:

  1. Elevated opening pressure
  2. High leukocyte count ( 1000/microl) predominantly lymphocytes
  3. Increased protein (100 - 800/mg/dl)
  4. Low glucose 
  5. AFB seen on direct smear of CSF

  • In tuberculous meningitis, the exudates tends to be most severe At the base of the brain
  • C.S.F. cell count in tubercular meningitis varies between 100-1000
  • Hemiplegia , quadriplegia, monoplegia , Cranial nerve palsies , Cerebral infarction,Ptosis,Decerebrate Rigidity,Tremors , Decorticate Rigidity, Midline cerebellar syndromes, Cerebellar Hemispheric Lesions are the neurological complications of tuberculosis meningitis
  • Most common cause of adrenal insufficiency in India is Tuberculosis
  • Characteristic finding in CT scan of patient with tubercular meningitis is Exudates seen in basal cistern
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