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Progression
Progression
In those people in whom TB bacilli overcome the immune system defenses and begin to multiply, there is progression from TB infection to TB disease. This may occur soon after infection (primary TB disease 1 to 5%) or many years after infection (post primary TB, secondary TB, reactivation TB disease of dormant bacilli 5 to 9%). The risk of reactivation increases with immune compromise, such as that caused by infection with HIV. In patients co-infected with M. tuberculosis and HIV, the risk of reactivation increases to 10% per year, while in immune competent individuals, the risk is between 5 and 10% in a lifetime.
About five percent of infected persons will develop TB disease in the first two years, and another five percent will develop disease later in life. In all, about 10% of infected persons with normal immune systems will develop TB disease in their lifetime.
Some medical conditions increase the risk of progression to TB disease. In HIV infected persons with TB infection, the risk increases to 10% each year instead of 10% over a lifetime. Other such conditions include drug injection (mainly because of the life style of IV Drug users), substance abuse, recent TB infection (within two years) or history of inadequately treated TB, chest X-ray suggestive of previous TB (fibrotic lesions and nodules), diabetes mellitus, silicosis, prolonged corticosteroid therapy and other immunosuppressive therapy, head and neck cancers, hematologic and reticuloendothelial diseases (leukemia and Hodgkin's disease), end-stage renal disease, intestinal bypass or gastrectomy, chronic malabsorption syndromes, or low body weight (10% or more below the ideal).
Some drugs, including rheumatoid arthritis drugs that work by blocking tumor necrosis factor-alpha (an inflammation-causing cytokine), raise the risk of causing a latent infection to become active due to the importance of this cytokine in the immune defense against TB.
TB disease most commonly affects the lungs (75% or more), where it is called pulmonary TB. Symptoms include a productive, prolonged cough of more than three weeks duration, chest pain, and hemoptysis. Systemic symptoms include fever, chills, night sweats, appetite loss, weight loss, and easy fatigability. The term consumption arose because sufferers appeared as if they were "consumed" from within by the disease. People from Asian and African descent may have more often lymph node TB than Caucasians.
Extrapulmonary sites include the pleura, central nervous system (meningitis), lymphatic system (scrofula of the neck), genitourinary system, and bones and joints (Pott's disease of the spine). An especially serious form is "disseminated", or "miliary" TB, so named because the lung lesions so-formed resemble millet seeds on x-ray. These are more common in immunosuppressed persons and in young children. Pulmonary TB may co-exist with extrapulmonary TB.
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