Tuberculosis

18 May

Tuberculosis

Tuberculosis (TB) was a leading cause of death in the United States until the 1940s, when antibiotics were developed that could effectively kill the bacteria that cause the disease (Mycobacterium tuberculosis). However, since the early 1980s, strains of the bacteria that are resistant to available drugs have developed, and tuberculosis has again become a major public health problem.

Mycobacterium tuberculosis (or M tuberculosis) is easily spread by coughing, sneezing, laughing, or singing but generally does not cause disease without repeated exposure. However, you can be infected with tuberculosis without hav- ing the active disease. This type of infection produces no symptoms and is known as a latent infection. Infection, with or without the active disease, results in a positive TB (or tuberculin) skin test.

Although anyone can contract tuberculosis, certain groups of people are at higher risk. This includes homeless people, poor and medically underserved people, prisoners, nursing home residents, intravenous drug users, people with alcoholism, people with HIV infection, people with AIDS, and people with any disease that reduces the effectiveness of their immune system. People who are in regular contact with at-risk populations are also more likely to become infected. People from countries with high rates of tuberculosis may bring the infection with them when they emigrate.

Active tuberculosis disease may produce no signs or symptoms other than a vague feeling of being ill. Sometimes the infection causes a cough that persists for more than 2 weeks and may produce bloody mucus. Other symptoms may include chest pain, difficulty breathing, fever, night sweats, fatigue, loss of appetite, and weight loss.

Because a latent infection with tuberculosis produces no symptoms, a person may be infected for years without realizing it. The infection may be discovered only after the person is examined or treated for another disease or through a rou- tine screening with the tuberculin skin test.

Active tuberculosis is diagnosed with a chest X ray and microscopic exami- nation and cultures of sputum samples expelled from the lungs. The tuberculin skin test is used both to screen people at risk for active tuberculosis and to iden- tify people with a latent infection.

Treatment depends on factors such as whether the TB is active or inactive, whether it has spread to other tissues, or whether the person has been treated for TB previously. Two or more antibiotics (such as isoniazid and rifampin) are given together daily for at least 6 to 9 months; some drug combinations can be given daily for the first month and then twice a week for an additional 8 months, although in some cases, treatment must continue for years. Warning: If the drug therapy is not strictly followed, the bacteria may mutate and become resistant to the drugs being used. If you do not take the drugs exactly as prescribed, you could have very serious problems.

Disorders of the Pleura The outside of the lungs and the inside of the chest cavity are lined by a con-tinuous membrane called the pleura

(see illustration). The portion of the pleura surrounding the lungs is called the visceral pleura, while the portion along the chest wall is called the pari- etal pleura. The pleural space is mois- tened with a small amount of fluid that allows the two sides of the lining to slide against each other easily during each breath. In a healthy person the two pleural surfaces are adjacent to each other and there is  little space between the two pleural membranes.

Tuberculosis

The Pleura

The pleura is a thin membrane with two layers that cover the lungs and chest cavity.Fluid between  the two layers provides lubrication and allows smooth expansion and contraction of the lungs during breathing.

Pleurisy

The pleura can become inflamed due to an infection of the underlying lung (such  as  pneumonia),  an  infectious

agent that enters the pleural space, injury (such as a rib fracture), and exposure to asbestos fibers. The pleura become swollen, and their surfaces may stick together rather than move freely when the person breathes. This causes chest pain that is aggravated by a deep breath or a cough. The pain may extend to the neck, shoul- ders, or abdomen on the affected side. Efforts to minimize the pain often lead to rapid, shallow breathing.

Because pleurisy is a symptom and not a disease or disorder, the only way to eliminate it is to treat the underlying cause. In the meantime, your doctor proba- bly will recommend that you take a nonprescription painkiller such as aspirin, ibuprofen, or acetaminophen. Also, you might be more comfortable if you wrap your chest with elastic cloth bandages, or if you clutch a pillow to the affected side to minimize chest wall motion during breathing.

Pleural Effusion

Heart failure, cancer, pulmonary embolism, infection, and inflammation can cause fluid to accumulate in the pleural space. The presence of any excess fluid in the pleural space is known as pleural effusion. Fluid can accumulate due to changes in pressure in the lymphatic or blood circulation of the pleural space, or to changes in the permeability of the pleural membranes. If blood accumulates in the pleural space, the condition is known as hemothorax. If pus is involved, the condition is called empyema.

Sometimes a pleural effusion is discovered by chance on a chest X ray that was taken for another purpose. Common symptoms include chest pain and shortness of breath. Identifying the cause of and determining the appropriate treatment for pleural effusion require removing and examining some of the fluid using a procedure called thoracentesis (see “Diagnostic Procedures,” page 256). A biopsy (removal of a small sample of tissue for examination under a micro- scope) of the pleural membranes also may be performed. To help the person’s breathing and relieve the discomfort associated with pleural effusion, and to help make a diagnosis, some or all of the fluid is drained with a needle or a tube. Treatment depends on the underlying cause of the fluid buildup.

Pneumothorax

Pneumothorax refers to the accumulation of air in the pleural space. It can result from a penetrating injury such as a rib fracture, or from diseases—such as emphysema, asthma, tuberculosis, or cystic fibrosis—that cause an air leak from the lung into the pleural space. Spontaneous pneumothorax can occur for no apparent reason in tall men younger than 40 and among people who scuba dive or engage in high-altitude activities such as mountain climbing.

Symptoms of pneumothorax include acute (sudden) pain on one side accom- panied by shortness of breath and, sometimes, a dry, hacking cough. However, you may experience less severe symptoms if only a small area of the pleural

space is involved or if the condition develops slowly. As with pleurisy, the pain may extend to other areas, such as the shoulder or the abdomen.

Your doctor can diagnose pneumothorax based on changes in breath sounds, as detected with a stethoscope, and with a chest X ray. A small, spontaneous pneumothorax will usually clear up on its own in a few days as the air is absorbed into surrounding tissues. In emergency situations the air may need to be drawn out with a needle or a tube inserted into the chest cavity to relieve pressure. With a larger or recurrent pneumothorax, surgical repair may be required.

Other Lung Disorders

The following less common lung disorders can occur under specific environ- mental circumstances or as a result of another disease or an injury. You should watch for symptoms of these conditions if you are at risk.

•  Adult respiratory distress syndrome (ARDS). This medical emergency often occurs within 24 to 48 hours after an acute respiratory illness or injury such as pneumonia,  chest  trauma,  severe  burns,  near-drowning, or  pulmonary embolism. The initial symptom is labored, shallow, rapid breathing. The skin may then turn blue due to lack of oxygen. ARDS usually occurs in a hospital setting and requires urgent attention including mechanical assistance to main- tain breathing.

•  Occupational lung disease. One type of occupational lung disease is black lung disease (anthracosis), which occurs among coal miners who have inhaled coal dust over the course of many years. Many other lung disorders can result from inhaling various substances (fumes or dusts) in the workplace. For exam- ple, silicosis, the oldest known occupational lung disease, results from repeated exposure to silica or quartz dust in occupations such as stone cut- ting, blasting, and mining. Berylliosis develops after exposure to beryllium, a metallic element used in the nuclear and aerospace industries and in the man- ufacture of electronics and chemicals. Irritant gases and fumes sometimes found in the workplace—including chlorine, phosgene, sulfur dioxide, hydro- gen sulfide, nitrogen dioxide, and ammonia—can cause permanent damage to the respiratory system. Inhalation of asbestos fibers can lead to a chronic lung disease called asbestosis. Possible complications of asbestosis include lung cancer (see page 247), pleural effusion (see previous page), and respiratory failure (a condition in which there is too much carbon dioxide and too little oxygen in the blood). Typical symptoms of occupational lung disease include a chronic cough and shortness of breath. Measures to prevent occupational lung disease include the use of protective gear and clothing and the enforce- ment of dust control standards, along with regular screening tests. Since the 1970s, asbestos has been replaced by safer materials whenever possible.

•  Hypersensitivity disease. This refers to allergic pulmonary disease that results from inhalation of organic dust or chemicals. Occupational exposure to poten- tial allergens (substances that cause allergic responses) such as molds and dust from hay, birds, sugarcane, mushrooms, barley, malt, cheese, wheat flour, straw, sawdust, humidifiers, air conditioners, and a variety of chemical manu- facturing processes can cause tumorlike granulomas to form inside the lungs. Once the lungs are sensitized to a specific allergen, the allergic response is rapid and severe. Symptoms include fever, chills, cough, shortness of breath, nausea, vomiting, and loss of appetite. The most effective treatment is to avoid all contact with the allergen, which will allow the granulomas to clear up on their own. If you are exposed to potential allergens at work, be sure to practice dust-control measures and wear appropriate protective gear such as a mask or a respirator.

•  High-altitude pulmonary edema. If work or recreation takes you to high alti- tudes, watch for possible symptoms such as increasing shortness of breath, weakness, irregular heartbeat, rapid pulse, abnormal breathing sounds, dizzi- ness, fatigue, and cough. Life-threatening high-altitude disorders can occur quickly after rapid ascents above 8,000 feet. Pulmonary embolism (see page 249) and pulmonary edema (fluid in the lungs) can occur if initial symptoms are ignored. The brain, heart, and muscles also can be affected by acute alti- tude sickness. A rapid descent to a lower altitude is the most effective treat- ment, but supplemental oxygen also should be used. To prevent this disorder, climbers should always make a gradual ascent, stop to rest at intermittent alti- tudes, and use supplemental oxygen as needed.

Diagnostic Procedures

The details about your symptoms of lung disease help your physician make an initial diagnosis. Tests of lung function and procedures to visualize your lungs are needed to confirm a diagnosis or to plan or monitor treatment. If your doctor thinks that you may have a lung disorder, you will likely undergo some of the following diagnostic procedures:

•  Spirometry. This is the simplest and most commonly performed lung function test. Spirometry is used to check or to evaluate a lung disorder and to monitor a person’s response to treatment. In this procedure the person takes a deep breath and exhales forcefully into the mouthpiece of a machine called a spirometer. The spirometer measures the total volume of air exhaled, which is the forced vital capacity (FVC), and the rate at which the air was exhaled, which is the forced expiratory volume in 1 second (FEV1 ).

•  Arterial blood gases test. This blood test is performed to determine the levels

of oxygen and carbon dioxide in the blood and the acidity of the blood. Sam-

ples of blood are drawn from an artery. This procedure is useful for diagnos- ing and monitoring respiratory failure.

•  Thoracentesis. If you have fluid in the pleural space, your doctor will insert a needle to draw some out. You will be awake, sitting upright, and leaning for- ward slightly. Your skin will be cleansed and anesthetized. The location at which the needle is inserted depends on where the fluid is located. This is determined by listening with a stethoscope, or by a chest X ray, ultrasound, or computed tomography (CT) scan.

•  Bronchoscopy. Your doctor may want to look directly into your lungs with a bronchoscope, a thin, flexible tube with a light and video camera at its tip. Your doctor also can use the bronchoscope to take samples of mucus and tis- sue from the lungs. Bronchoscopy can be used for both diagnosis and treat- ment, such as removing foreign bodies and clearing unwanted fluids. The procedure is performed while you are awake and lying on your back. You will be sedated and given adequate pain medication. The doctor also will give you medication to keep you from gagging or coughing during the procedure. Oxy- gen is delivered to your lungs via a tube that has been passed through one nos- tril; the bronchoscope will be threaded through your mouth or the other nostril. Your doctor will watch the video display as the bronchoscope moves through the airway into your lungs. These images also will be recorded on videotape, and the most helpful images will be printed out.

•  Thoracotomy. When a bronchoscopy is insufficient to make a diagnosis or shows problems that require more thorough evaluation, your doctor may recommend an endoscopic examination of the pleural space. During the examination, the doctor may perform either of two minor surgical proce- dures—a mediastinoscopy or a thoracoscopy. If the problem is more exten- sive, you may need to have a major surgical procedure called a thoracotomy. You will have general anesthesia for a thoracotomy, in which the chest cavity is opened and the lungs and surrounding tissues are examined. Pieces of tissue will be removed for laboratory analysis, and the overall state of the respiratory system will be assessed. Often this can be achieved through a small incision between the ribs. Sometimes a larger surgical opening must be created.

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