TB can affect any part of the body. Tuberculosis (TB) being an airborne infection, is caused by the bacteria Mycobacterium tuberculosis (MTB). It is transmitted through the droplet nuclei containing the bacteria and are emitted by a patient suffering from active pulmonary TB. It is symptomized by sudden weight loss, coughing out blood with or without mucus, fever and night sweats.
Depending on the pathophysiology and body's reaction to the bacterium, TB can be active (transmissible form where the host shows classic symptoms) or latent (dormant but viable bacterium is sequestered within lesions formed in the lungs).
People who consider TB as a lung disease, get astonished after hearing about someone suffering from abdominal TB or TB of joints. Yet, in addition to pulmonary TB, another form of TB is Extrapulmonary Tuberculosis (EPTB) which affects the organs other than lungs. In India, of all TB cases between 15-20% are of EPTB in immunocompetent individuals while 50% of HIV infected patients suffer from Extrapulmonary Tuberculosis.
Tuberculosis: Traveling Beyond Lungs
Pulmonary TB is characterized by lung infection and the pathogenesis starts as soon as the bacilli reach the alveoli and replicate within the localized macrophages. These cells interact with T lymphocytes and differentiate into histocytes that aggregate along with lymphocytes and form the granulomas which are the characteristics of TB. Those at greatest risks are, people with altered cell immunity, those suffering from malnutrition, HIV infected patients, the very young and the very old as well as those with end-stage renal disease and diabetes.
Extrapulmonary Tuberculosis occurs in 10-42% of adult TB patients depending on race or ethnic background, age, presence or absence of underlying disease, genotype of the Mycobacterium strain, and immune status. The lung being the primary site of infection, Extrapulmonary Tuberculosis infection initiates when the bacilli gain access to other regions of the body through blood or lymphatic system. EPTB may present with constitutional symptoms such as fever, anorexia, unexpected weight loss, malaise and fatigue. Additional symptoms are dependent on the organ and systems affected. The most common forms of Extrapulmonary Tuberculosis include lymphatic, pleural, bone and joint disease. Pericardial, meningeal and disseminated TB have greater rates of fatal outcome.
Different Organs Affected By Tuberculosis
- Lymph Node TB- It is the most common form of EPTB seen in India and considered as the local presentation of a systemic disease. It occurs when the bacteria spreads to the lymphs, with hilar and mediastinal lymph nodes involvement. It can occur during primary infection or reinfection post latency. It mostly manifests as enlarged lymph nodes.
- Tuberculous Pleural Effusion- Pleural effusion is the build-up of fluid in the lungs and the presence of inflammatory cells in the pleural space. It is one of the most common forms of EPTB, predominant in men, and manitests as tever, cough and chest pain.
- Bone and Joint TB-It affects spine, long bones and the joints. Infrequently, tuberculous bacilli travel from the lung to the spine along the Batson paravertebral venous plexus or by lymphatic drainage to the para aortic lymph nodes. The symptoms often progress over weeks and months, accompanied with back pain occasionally associated with abdominal pain.
- Abdominal TB-It includes TB of the gastrointestinal tract, peritoneum and intra-abdominal organs including liver, spleen and pancreas. Hepatobiliary and pancreatic TB are seen more often in immunocompromised individuals and manifest as anorexia, malaise, low grade fever, night sweats and obstructive jaundice. Splenomegaly is seen in patients with disseminated TB.