Lymphangioleiomyomatosis (LAM) is a rare lung disease that affects almost exclusively women, which occurs in the presence and absence of tuberous sclerosis complex (TSC-LAM) or sporadic (S-LAM), respectively. LAM is characterized by an unusual type of muscle cell that invades the tissue of the lungs, including the airways, and blood 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 muscle cells are not considered cancerous, they grow without the usual controls within the lungs. Over time, the muscle cells block the flow of air, blood, and lymph vessels to and from the lungs, preventing the lungs from providing oxygen to the rest of the body.
The most common presentation of LAM is progressive dyspnea on exertion, often in association with a history of pneumothorax or chylothorax (other symptoms of LAM include chest pain and coughing). The histopathological hallmarks of the disease are dilated distal airspaces and diffuse infiltration of the pulmonary interstitium with atypical smooth muscle cells, including spaces surrounding airways, vessels, and lymphatics. The differential diagnosis of the thin walled cystic change that is characteristic of LAM also includes emphysema, pulmonary Langerhan's cell histiocytosis (PLCH), lymphocytic interstitial pneumonitis, Birtt Hogg Dubé syndrome, and Sjogren's syndrome. Rare syndromes of benign or malignant smooth muscle metastasis may also produce cystic change and closely mimic LAM, including benign metastasizing leiomyoma, endometrial stromal sarcomas, and low-grade leiomyosarcomas. Classical methods of diagnosing LAM disease include chest X-rays, high-resolution CT scans and lung biopsies (e.g., thoracoscopy, open biopsy and transbronchial biopsy).
Because many of the early signs and symptoms of lymphangioleiomyomatosis (LAM) are similar to those of other lung diseases, including asthma, emphysema and bronchitis, LAM can be difficult to diagnose. Thus, there remains a need in the art for a diagnostic assay to differentiate LAM disease from other respiratory disorders.