Tuberculosis, or TB, is a bacterial disease that almost invariably infects the lungs, but can also spread to almost any organ system to cause disease and symptoms. This is the reason why screening and treatment are pursued vigorously, so much so that legal mandates have been passed with different requirements depending on a person’s TB status.
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TB invariably begins in the lungs, as it is transmitted via the air. The most common symptom is cough, and with extensive lung involvement the cough becomes productive, first with mucus and eventually with blood as well. The infection usually affects the upper lobes of the lungs, and can often erode into a blood vessel, thus spreading to the rest of the body. Damage to the lung tissue can occur over time, and can even be irreversible after a point.
This is also known as miliary TB, and often occurs in immunocompromised patients (such as HIV patients) or after extensive pulmonary disease leads to the spread of TB via the bloodstream. It can affect any organ, but most commonly attacks the liver, bone marrow, kidneys, adrenal glands and spleen. Symptoms can vary depending on the organ involved, from decreased oxygenation of the blood to a widespread bacterial infection of the blood (sepsis), and can be fatal much of the time.
The lymphatic system (such as the lymph nodes) are one of the primary TB infection sites outside of the lungs. The lymph nodes can also aid in TB's dissemination, and an infection here presents as painless swelling of the lymph nodes. The lymph nodes can compress other structures, such as the airway.
TB can also spread to the pleura, which are the layers of tissue that enclose the lungs. This can often result in a condition known as pleural effusion, which is a collection of fluid (often infected with TB) that develops between the pleural layers and the lungs, and can cause problems with breathing and oxygenation. If the fluid is infected, it is known as empyema, and can necessitate surgical drainage.
TB of the Genitourinary System
TB can also infect the kidneys, genitals and ureters. The symptoms are usually localized to where the infection is present, and common manifestations include pain on urination, blood in the urine and increased frequency of urination. The effects on the kidney can be quite damaging but are uncommon, and include renal failure, kidney stones and high blood pressure (hypertension).
Bone and Joint TB
Infection of the bones and joints with TB also occurs, and the risk increases with age. The usual symptoms are pain, swelling of the involved joint and sinus tracts (tunnels in the tissue that lead from the joint out to the external skin). Treatment is usually undertaken with medication, and surgery is typically done when the spine becomes involved, which can manifest in compromised nervous system symptoms.
Central Nervous System TB
The most common infection of the central nervous system with TB is meningitis. This usually occurs with direct bacterial infection, and can infect the meninges or the brain tissue (encephalitis). The disease primarily attacks the base of the brain, and manifests with headache, decreased level of consciousness and a stiff neck. These patients also tend to have miliary TB occurring in the rest of their body when the nervous system starts showing symptoms. Occasionally, a focal lesion can develop instead of meningitis; this is known as a tuberculoma, and is often asymptomatic except for local effects produced by its mass impinging on other tissues.
TB can infect the pericardium, which is the tissue that covers the heart. It can result in a buildup of fluid between the pericardium and the heart tissue, known as pericardial effusion. Fibrosis can also result with the scar tissue causing constriction of the heart. Also, infection of the heart tissue such as the atria and left ventricle can result, which has obvious damaging effects on cardiac function.