Definition of Lymphangioleiomyomatosis

Lymphangioleiomyomatosis: A lung disease characterized by an unusual type of muscle cell that invades the tissue of the lungs, including the airways, blood vessels, and lymph vessels. Over time, these muscle cells form into bundles and grow into the walls of the airways and blood and lymph vessels, causing them to become obstructed. Although these cells are not considered cancerous, they act somewhat like cancer cells in that they grow uncontrollably throughout the lung. The muscle cells in time block the flow of air, blood, and lymph to and from the lungs, preventing the lungs from providing oxygen to the rest of the body.

"Lymphangioleiomyomatosis" is pronounced lim - fan' je - o - li' o - mi' o - ma - to' sis. "Lymph-" and "-angio-" refer to the lymph and blood vessels. "Leiomyomatosis" refers to the formation of the bundles of the unusual muscle cells. Lymphangioleiomyomatosis is abbreviated LAM.

Cause: LAM can occur in association with tuberous sclerosis due to mutations in the tuberous sclerosis complex (TSC) genes TSC1 or TSC2 genes. Sporadic (isolated) caes of LAM typically result from 2 somatic mutations in the TSC2 gene, although a fraction of sporadic LAM is caused by germline mutations in the TSC1 gene.

Frequency: The precise number of people with LAM is not known. It has been estimated that there may be up to several hundred women in the US with it.

LAM almost exclusively affects women of childbearing age, although several cases have been reported in which the disease was thought to have developed after menopause. The international literature also includes reports of a few cases in men.

Symptoms: A common symptom of LAM is shortness of breath (dyspnea). In the early stages of disease, there may be dyspnea only during strenuous exercise, but as the disease advances, even at rest there may be shortness of breath. Another common symptom is chest pain. Occasionally, patients cough up small amounts of blood.

The symptoms are caused by the excessive growth of the muscle cells around the airways, and blood and lymph vessels. The excess muscle cells can block the airways, trapping air in the smallest air compartments in the lung (alveoli) and causing the person to have difficulty moving air out of the lungs. This results in a breakdown of the lung tissue and the formation of small cysts (air-filled cavities).

Cysts near or on the surface of the lung (blebs) can rupture and, as air leaks from the lung into the chest cavity (pneumothorax), the lung or a part of the lung can collapse, causing pain. If the amount of air that leaks out is small, the lung may seal over the space and re-expand itself. If air continues to leak into the chest cavity, however, it may be necessary to re-expand the collapsed portion of the lung by removing the air that has leaked into the chest cavity. This is an in-patient procedure, done using tube inserted through the chest wall into the chest cavity.

The excessive muscle growth may also block blood vessels in the lung, causing them to become distended with blood and even to rupture. This can result in the patient coughing up blood-stained sputum or blood (hemoptysis).

Obstruction of the lymphatic vessels by the excess muscle growth can lead to leakage of fluid into the chest cavity (pleural effusion). The fluid may be straw-colored (lymph), or fat-containing, milky white (chyle), or pinkish-red if it contains blood. A physician can remove some of this fluid with a needle and syringe to determine its composition and origin. If large amounts of this fluid accumulate in the chest cavity, it may have to be removed through a tube surgically inserted into the chest.

About 30 to 50% of patients with LAM develop leakage of air into the chest cavity (pneumothorax), and up to 80% have leakage of fluid into the chest cavity (pleural effusions). Coughing up blood-stained sputum or blood (hemoptysis) is less frequent.

Course: LAM is generally progressive, leading to increasingly impaired lung function. The rate of development can vary considerably among patients. As the disease advances, there is more extensive growth of muscle cells throughout the lung and repeated leakage of fluid into the chest cavity (pleural effusions). As an increasing number of cysts are formed, the lung takes on a honeycomb appearance.

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