Tuberculosis is an infectious disease caused mainly by Mycobacterium tuberculosis, less commonly – Mycobacterium bovis. M.tuberculosis primarily affects lungs but may also disseminate throughout the body affecting various organs. The infection may lie latent within healed, fibrotic and/or calcific granulomata for the whole life. Under certain circumstances granulomas break down, mycobacteria start to replicate causing the development of symptomatic disease also known as active tuberculosis.
Factors associated with the increased the risk of developing active disease
Factors which impair the immunity are associated with an increased risk of tuberculosis including:
- HIV infection is one of the most important and the most common comorbidities related to TB. It is suggested that HIV/AIDS increases risk of developing TB up to 37 times. ;
- Malnutrition and causative disorders are associated with weakened immunity and, respectively, with the risk of developing TB;
- Intravenous drug abuse is a known risk factor for HIV and TB an also associated with poor adherence to treatment and drug-resistance;
- Immunosuppressive/corticosteroid therapy inhibits natural body defense mechanisms and, respectively, those who receive such treatment are at risk of developing TB;
- Diabetes mellitus, chronic renal failure and hemodialysis are known to affect a person’s immune system, so it impairs body’s ability to resist infection;
- Vitamin D deficiency is associated with impaired immune response ;
- Alcohol abuse is known to increase risk of TB by 3 times and is also associated with poor treatment adherence, which in turn increases risk of developing multiple drug-resistance;
- Silicosis and other chronic lung diseases interfere with macrophageal system and increase the probability of developing TB;
- Smoking increases the risk of TB two-threefold. Along with tuberculosis smoking damages lungs and therefore is associated with poor treatment results. If the person who suffers from tuberculosis is smoking he/she is recommended to quit smoking;
Secondary tuberculosis occurs due to the reactivation of the latent infection. It typically affects the apical and posterior segments of the upper lobes of the lungs. The superior segments of the lower lobes may also be involved.
A cough lasting longer than for 3 weeks with the discharge of sputum is suggestive of tuberculosis. Initially the cough may be dry/nonproductive and typically occurs in the morning, but later it becomes productive with the discharge of sputum. The sputum may have different appearance: it may be clear, green or yellowish (purulent sputum), it may contain various amounts of blood – from a few spots to sudden episodes of cough with large amounts of blood (hemoptysis) due to the erosion of of a pulmonary blood vessel.
Subpleural lesions (meaning that these lesions are located close to the surface of the lung, right under the pleura) and involvement of the pleura may cause chest wall pain which worsens on breathing and coughing.
If the large areas of the lungs are affected breathlessness (dyspnea) develops which significantly worsens the course of the disease and person’s well-being.
Other symptoms are nonspecific:
- Loss of weight;
- Low-grade persistent fever and sweating;
- General malaise;
- Loss of appetite (anorexia);
- Tuberculous lymphadenitis (scrofula disease) is one of the most common extrapulmonary manifestations of tuberculosis, characterized by an inflammation of the cervical lymph nodes. Typically on the neck are detected as unilateral, less frequently – bilateral painless enlarged firm cervical node/nodes with unchanged skin over them.
- Pleural tuberculosis occurs when the pleura is involved.
- Tuberculosis of the upper airways develops in case of advanced cavitary tuberculosis. The larynx, pharynx and epiglottis may be affected resulting in hoarseness, dysphonia and impaired swallowing.
- Genitourinary tuberculosis causes frequent urination, difficulties and pain while urinating, hematuria (bloody urine) and abdominal/flank pain.
- Bone tuberculosis typically affects weight-bearing joints – the spine, knees and hips leading to pain in these joints, swellings and movements limittions.
- Tuberculous meningitis develops when mycobacteria get into the subarachnoid space. Symptoms include headache and slight mental changes after a low-grade fever, malaise, anorexia, and irritability for severl weeks. Innervations of the face may also suffer.
- Miliary/disseminated tuberculosis occurs due to hematogenous spread of the bacilli all over the body causing the corresponding symptoms.
Diagnosis of active tuberculosis
A diagnosis of active tuberculosis is made based on the results of chest X-rays and multiple sputum cultures (at least three) for Mycobacteria tuberculosis. Tissue biopsy may also be performed, especially for extrapulmonary tuberculosis.