Types of TB

TB is generally divided into pulmonary tuberculosis & extrapulmonary tuberculosis.

Pulmonary Tuberculosis is further divided into five different types of TB, which includes

• Primary TB pneumonia which presents itself in the form of pneumonia and is highly contagious
• Laryngeal TB which affects the throat (the vocal chord area) and it is also contagious
• Cavitary TB tends to form large cavities in the lungs and is a highly contagious form of TB
• Miliary TB is characterized by the appearance of small granules in the lungs visible through a chest x-ray
• TB Pleurisy usually develops shortly after catching the infection and is characterized by shortness of breath, chest pain and fluid in the lungs

Extrapulmonary TB is further divided into seven different types of TB, which includes

• Adrenal Tuberculosis affects the adrenal glands
• Lymph node disease is characterized by the patients experience enlargement of the lymph nodes. The nodes can also rupture through the skin.
• Osteal Tuberculosis affects the bones. The affected bone tissue weakens and this could cause fracture of the affected area.
• TB Peritonitis usually affects the outer lining of the intestine and due to this; the fluid gets collected in the outer lining of the intestine giving rise to pain in the abdomen.
• Renal TB is characterized by the patient experiencing pyuria (the presence of white blood cells in the urine)
• TB Meningitis patients display signs of being affected by a stroke or a brain tumour. It is extremely dangerous condition
• TB Pericarditis is a form of TB characterized by an increase in the amount of fluid around the heart, and this could also hamper its function

TB can also be classified as

• Latent TB infection means a person has TB bacteria but is not affected by them. Therefore, it is not contagious
• TB Disease means that the person has TB bacteria and they will multiply to cause infection

Source of Infection

There are two sources of infection – Human and Bovine

• Human Source: The most common source of infection is the human case whose sputum is positive for tubercle bacilli and who has either received no treatment or not treated completely. Such sources can discharge the bacilli in their sputum for years.
• Bovine source: The bovine source of infection is usually infected milk.

Symptoms

• Sometimes asymptomatic and is detected on routine check-up
• Anorexia, weakness and undue fatigue
• Evening rise of fever (specially a low grade fever)
• Cough with or without expectoration
• Haemoptysis (blood in the sputum) in later stages
• Difficulty in breathing
• Chest pain

Suggested Investigations

• CBC (Complete Blood Count) - to check the heamoglobin levels and RBC and WBC count
• ESR (Erythrocyte Sedimentation Rate) - to check if is raised as the values increases in infections
• X-ray Chest - to see the cavities, masses and scars formed due to infection
• CT-Scan - to confirm the diagnosis of tuberculosis and to differentiate it from other diseases
• Sputum AFB (Acid Fast Bacilli) - to confirm the presence of TB bacilli before starting the TB treatment
• Tuberculin/Mantoux Test – to confirm if the person has got active Tuberculosis or not
• Tuberculous antigen and antibody in the fluid and serum - to confirm the TB diagnosis from cerebrospinal fluid or pleural fluid etc

Treatment of Tuberculosis

Treatment for TB consists of antibiotics (chemotherapy) to kill the bacteria.

The standard first line group of drugs comprises of Isoniazid (INH), Rifampicin (RMP), Prazinamide (PZA), and Ethambutol (EMB). INH is bactericidal against the replicating bacteria. EMB is bacteriostatic at low doses, but for TB treatment, it is used at higher bactericidal doses. RMP is bactericidal and has a sterilizing effect whereas PZA is only bactericidal.

(Bacteriostatic antibiotics limit the growth of bacteria by interfering with bacterial protein production, DNA replication, or other aspects of bacterial cellular metabolism, whereas, bactericidal antibiotics kills the bacteria.)

Active TB disease is best treated with combinations of several antibiotics while Latent TB treatment usually uses a single antibiotic The standard course of treatment for active TB is isoniazid, rifampicin, pyrazinamide, and ethambutol for two months, followed by isoniazid and rifampicin alone for a further four months. The patient is considered cured at six months although the chances of relapse (2-4 %) are there. For latent tuberculosis, the standard treatment is six to nine months of isoniazid alone.

Second line group of drug are those that are less effective than the first-line drugs and/or may have toxic side effects, or it may be unavailable in many developing countries. Example: Amikacin, Kanamycin, Ciprofloxacin, Para-aminosalicylic acid etc.

Third line group of drugs are those which are not very effective or because their efficacy has not been proven. Example: Rifabutin, Clarithromycin, Linezolid, Thioridazine, Arginine, etc.

The usefulness of corticosteroids (prednisolone or dexamethasone) in the treatment of TB is proven for TB meningitis and TB pericarditis. Vitamin Supplements are given to the patients to save them from the deficiencies the TB treatment can cause.

DOTS:

DOTS stands for ‘Directly Observed Therapy, Short-course’ implemented by WHO. If the organism is known to be fully sensitive, then treatment is with Isoniazid, Rifampicin, and Pyrazinamide for two months, followed by Isoniazid And Rifampicin for four months. Ethambutol need not be used.

Patients who do no take their TB treatment in a regular and reliable way are at greatly increased risk of treatment failure, relapse and development of drug-resistant TB strains. And the reasons for such non-compliance are:

• Loss of motivation due to resolving of symptoms within first few weeks of TB medications
• Increased size and number of tablets especially PZA tablets
• Requirement of the medicine dose to be taken on empty stomach for better absorption

Risk of developing adverse effects with anti-TB drugs is high in people with age >60 yrs, females, HIV positive patients, etc.

Resistance to TB treatment occurs due to following reasons:

• Infection with a resistant strain of TB
• Not taking the prescribed regimen appropriately
• Using low quality medication

MDR-TB & XDR-TB:

• Multi-drug resistant tuberculosis (MDR-TB) is defined as TB that is resistant at least to Isoniazid and Rifampicin. Cases that are resistant to any other combination of anti-TB drugs but not to INH and RMP are not classified as MDR-TB.
• Extensively drug-resistant tuberculosis (XDR-TB) is a form of TB which is caused by bacteria that is resistant to the most effective anti-TB drugs. It has emerged from the mismanagement of multidrug-resistant TB. It can spread from one person to another just as tuberculosis spread. It is extremely difficult to treat XDR-TB
• The treatment and prognosis of MDR-TB and XDR-TB are similar to that for cancer than that for infection as the mortality rate of up to 80%. Treatment courses are a minimum of 18 months and may last years. It may require surgery though death rates remain high despite optimal treatment. The treatment of MDR-TB must be undertaken by a physician experienced in the treatment of MDR-TB.

BCG Vaccine:

• BCG vaccine is a live bacterial vaccine for protection against tuberculosis (childhood tuberculosis), given as early as possible after birth upto 5 yrs of age. It would be effective only if given before the child comes in contact with tuberculosis.
• If it is given beyond 6 months it is preferable to do a prior Mantoux test (MT) to see if the patient is already sensitized to tuberculosis. If patient is already sensitized as shown by positive MT, BCG is not necessary.
• BCG being live vaccine itself induces a benign primary infection, which leads to some immunity. Such a child when comes in contact with a patient with tuberculosis can still catch the wild germ and develop primary TB but the spread will be mostly prevented by previous BCG immunity. Hence, such children will not develop serious forms of childhood tuberculosis.
• Note that BCG does not prevent adult type of tuberculosis.

Prevention

• All patients with the following symptoms should get investigated for TB
  - Cough for more than four weeks
  - Low grade evening rise of fever
  - Chest pain
  - Haemoptysis ( blood in the sputum)
• The close contacts of the person who is suffering form TB should also be investigated for TB or should take proper precautions
• Some sanitary practices like covering of mouth and nose while coughing or sneezing and not spitting on roads or other premises, will also save the spread of this infection
• BCG vaccination of the infants protects them from severe forms of TB like TB Meningitis and Miliary TB
• The chemotherapy for TB should be completed and not discontinued on feeling a little better as this will give rise to developing of resistant bacterial strains which are very difficult to be cured