Brain Tuberculosis - Pathogenesis, Complications, Diagnosis, and Management

What Is Brain Tuberculosis?

Tuberculosis (TB) is a frequently occurring infectious disease in developing countries, including India. It mostly affects the lung parenchyma, but in advanced cases, it can even spread to the brain and other organs of the body. When the tuberculous infection affects the brain and its surrounding membranes, it is known as brain tuberculosis. It may also be called tubercular meningitis or meningeal tuberculosis when it affects the tissues of the brain and the spinal cord. The condition may become life-threatening if not treated promptly.

What Are the Causes of Brain Tuberculosis?

Brain tuberculosis is caused by the bacterium Mycobacterium tuberculosis. The bacteria travel through the blood to reach the brain and spinal cord from the lungs. Brains tuberculosis is an uncommon disease in the United States. Mostly it occurs in patients who visit the United States from other developing nations where TB is common. There are some risk factors that predispose an individual to tuberculosis infection. These include:

• Human immunodeficiency syndrome.

• Excessive alcohol consumption.

• Poor immune response.

• Pulmonary tuberculosis (lung tuberculosis).

• Diabetic patients.

• Poor weight and malnourished children.

• Chronic renal failure.

• Cancer.

• Use of chemotherapy.

What Parts of the Brain Are Affected by Tuberculosis?

• Tuberculosis of the brain can affect the parenchymal and meningeal tissues of the central nervous system.

• The infection mainly spreads through the bloodstream via hematogenous dissemination. The bacterium Mycobacterium tuberculosis can cross the blood-brain barrier and reach the brain.

• It affects the meninges of the brain. This is called meningeal tuberculosis.

• Tuberculosis in the brain can also form soft, caseous necrotic lesions in the brain parenchyma known as tuberculomas.

• The brain's frontal lobe is most commonly affected, followed by the parietal and temporal lobes of the brain. The occipital lobe of the brain is the least commonly affected.

What Is the Pathogenesis of Brain Tuberculosis?

Dormant bacteria residing in an individual’s body can reactivate and travel through the blood to reach the brain. This bacterium has the potential to cross the blood-brain barrier and reach the tissues of the brain. TB of the brain usually develops in two main steps.

• Tuberculoma Development: Small, soft, caseous necrotic (dead) foci lesions are formed in the brain leading to bacteremia. These small lesions then tend to coalesce to form large granulomatous tuberculous lesions called tuberculomas. These tuberculomas are characterized by central caseous (cheese-like cell death) necrosis, epithelioid cells, chronic inflammatory cell infiltration, and multinucleated giant cells.

• Tuberculous Meningoencephalitis: It is a fatal and serious form of brain tuberculosis. Tuberculoma formation can progress to vasculitis, cerebritis, tuberculous abscess (when cavities are formed within the tuberculomas and they are filled with fluid or pus), diffuse meningitis, and even stroke. The necrotic infected foci can burst and lead to the development of other types of brain tuberculosis. This depends on which part of the brain the infected content is poured. Tuberculous meningoencephalitis is a devastating condition.

What Are the Clinical Signs and Symptoms of Brain Tuberculosis?

Some of the symptoms develop gradually over a period of one to four weeks and usually include:

• Low-grade fever with chills.

• Nausea with frequent episodes of vomiting.

• Mental instability.

• Tiredness.

• Body malaise.

• Lethargy.

• Mental confusion.

• Mood irritability and agitation.

• Reaction to light.

• Severe headache.

• Meningismus (stiff neck and headache).

• Seizures.

• Poor consciousness in young children.

• Soft spots (protruding fontanelles) in young babies.

• Loss of appetite.

• Spasms of the back and neck muscles lead to an arched neck, head, and spine.

How Is Brain Tuberculosis Diagnosed?

It is quite challenging to diagnose brain tuberculomas that are usually asymptomatic. The healthcare provider can perform the following diagnostic tests.

• Physical Examination: The doctor should physically examine the patient and check for all the signs and symptoms.

• Medical History: It is very important to ask the patient about his previous encounter with tuberculosis infection because many times, the bacteria remains latent and dormant in a person’s body and can reactivate later in life.

• Lumbar Puncture (Spinal Tap): This is an invasive procedure wherein a small amount of cerebrospinal fluid is collected from the spinal cord for laboratory analysis. This test is used to confirm brain tuberculosis.

• Brain Imaging Techniques: The imaging techniques can be carried out to look for tuberculous abscesses, tuberculomas, and neoplastic lesions. A computed tomography scan of the head and magnetic resonance imaging is generally carried out.

• Biopsy of the Brain: The biopsy of the brain is usually done in rare cases.

What Is the Treatment of Brain Tuberculosis?

The mainstay treatment of brain tuberculosis includes antitubercular drugs (Isoniazid, Rifampin, Pyrazinamide, and Ethambutol). This therapy is supported by adjunctive drug therapy, including corticosteroids and decongestant medications. Adjunctive drug therapy helps to alleviate the risk of progressive brain damage and minimize mortality rates. Usually, the first-line antitubercular drug therapy is given for 12 months. Steroid therapy is usually given for a period of two months. It is very important to consult a doctor at the earliest as the symptoms appear in a person. Sometimes children may require anti-epileptic drugs to control seizures. Sometimes, very large tuberculomas may require surgical excision in a hospital.

What Are the Complications of Brain Tuberculosis?

The disease can progress and cause the following complications:

• Brain cell death.

• Brain damage.

• Loss of hearing.

• Edema (swelling) inside the brain causes an increased buildup of fluid pressure, causing hydrocephalus.

• Seizures.

• Brain stroke.

• Death.

How to Prevent Brain Tuberculosis?

The best way to prevent brain tuberculosis is to prevent the occurrence of tuberculosis infection in a person. Efforts should be made to vaccinate every child against TB. BCG (Bacillus Calmette-Guerin) vaccine helps to prevent the spread of the infection. One should maintain personal hygiene and make efforts to improve immunity in a child or an adult. It is also important to cure people with dormant states of the disease to prevent the spread of the infection.

Conclusion

Brain tuberculosis is an infection of the tissues of the brain that can lead to serious outcomes of the disease if left untreated. In rare cases, it can become fatal and may even cause death. Therefore, it is important to consult a doctor as soon as the symptoms appear, and the treatment should not be delayed. It is also crucial to get young children vaccinated for the BCG vaccine to prevent the spread of the disease. Diagnosis is made through brain imaging techniques, and the treatment mainly includes the regimen of four antitubercular drugs.