Tuberculous meningitis: What to know

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TB is an infection caused by Mycobacterium tuberculosis (M. tuberculosis) bacteria. The infection primarily affects a person’s lungs, though it may also affect areas outside the lungs. Doctors refer to this as “extrapulmonary TB.”

TBM is a rare extrapulmonary manifestation of TB that affects the brain and spinal cord. It accounts for around 1% of cases of extrapulmonary TB.

As a 2021 review explains, the mechanism by which M. tuberculosis spreads to the brain is complex. First, the bacteria must move from the lungs and into the bloodstream or lymphatic system. It can do so by “hijacking” or passing through other cells.

The bacteria then cross the blood-brain barrier and blood-cerebrospinal fluid barrier. These barriers ordinarily help protect the brain from harmful chemicals and pathogens.

Once inside the brain, the bacteria encounter little resistance, as the brain has a very limited immune response. The bacteria replicate, causing bacteria-filled brain lesions. These lesions eventually rupture, causing M. tuberculosis to flood into the brain’s meninges.

Not everyone who develops TB will go on to develop TBM.

If TBM does occur, its severity will vary from person to person. Scientists have discovered several risk factors that affect the probability and severity of TBM. A 2019 review lists these as follows:

• Age: Children between ages 2–4 years are at increased risk of developing tuberculosis infections, and of those infections leading to TBM.
• HIV: Adults who have HIV are more likely to develop TBM compared with adults who do not have HIV.
• Malnutrition: There is some evidence to suggest that malnutrition could increase a person’s risk of developing TB. This risk may be higher for people who are deficient in vitamin D.
• Bacterial strain: Some strains of M. tuberculosis are more likely to lead to extrapulmonary TB.
• Immunodeficiency: Congenital or acquired immunodeficiency conditions, as well as immunosuppressive medications, can also increase risk.

It is important to distinguish the general symptoms of TB from those that are specific to TBM.

A 2022 review lists the following general symptoms of TB:

• chronic cough
• blood in the sputum
• weight loss
• fever
• night sweats

If TB develops into TBM, a person will experience additional extrapulmonary symptoms. These may develop in stages over days or weeks and may include:

• headache
• dizziness
• vomiting
• general malaise
• personality changes

If TBM progresses further, more serious symptoms may develop. Examples include:

• severe headache
• neck stiffness
• confusion
• altered mental state, perhaps causing marked behavioral changes
• cranial nerve damage
• difficulty controlling the body
• coma
• seizures
• weakness, including loss of power in specific limbs
• sensation loss

Without treatment, TBM is fatal.

To diagnose TBM, doctors must conduct a cerebrospinal fluid (CSF) analysis. This test involves inserting a needle between the lower spine vertebrae and drawing out a sample of CSF for laboratory analysis. The analysis will help doctors determine whether a person has meningitis and whether the meningitis is TBM.

If a CSF analysis is not possible, but the doctor has a high clinical suspicion of TBM, they may choose to proceed with treatment for TBM.

Doctors may also use MRI and other imaging techniques to assist the diagnosis.

Some potential complications of TBM include:

• Hydrocephalus: This is a buildup of fluid in the brain.
• Vasculitis: This describes inflammation of the blood vessels.
• Stroke: This is an interruption or reduction in blood flow to part of the brain.
• Hyponatremia: This describes abnormally low blood sodium levels.

The treatment for TBM is similar to that of other forms of meningitis. A doctor will prescribe antibiotic drugs such as:

• isoniazid
• rifampin
• streptomycin
• ethambutol

People typically continue antibiotic treatment for 9–12 months.

Doctors will also prescribe corticosteroid medications to reduce inflammation and swelling of the meninges.

Tuberculosis is a serious condition, regardless of whether it develops into TBM. Without treatment, the mortality rate for TB is greater than 50%. As such, anyone with symptoms of TB or TBM should contact their doctor immediately.

Very young children are at increased risk of developing TBM. For this reason, parents and caregivers should seek immediate medical advice if a child develops signs and symptoms of TB or TBM.

Some TBM signs and symptoms that are more likely to affect children include:

• mood changes, such as irritability and apathy
• headache
• neck stiffness
• sensitivity to light
• nausea
• vomiting
• problems with eye movement
• weakness or loss of muscle control

TBM is a serious condition that is fatal without treatment. Even with treatment, TBM has a mortality rate of 20–67%. People with a greater risk of mortality include:

• young children
• older adults
• people living with HIV
• people who have antitubercular drug resistance
• people with conditions that compromise their immune system

Early diagnosis and treatment for TB can help prevent the condition from developing into TBM. Likewise, early diagnosis and treatment for TBM can help reduce the risk of complications and death.

TBM is a serious extrapulmonary manifestation of TB. With TBM, M. tuberculosis infects the brain and spinal column, resulting in inflammation of the meninges.

Without treatment, TBM is fatal. Early and prolonged antibiotic treatment can help reduce the risk of complications. The best way to help prevent TBM is to treat TB before the bacterium can enter the bloodstream and cross the blood-brain barrier.

Anyone who experiences symptoms of TB or TBM should contact their doctor immediately, especially if they belong to a high risk group. Examples include young children, older adults, and people living with HIV.