The consequences of vessel and airway obstruction include chylous fluid accumulations, hemoptysis, airflow obstruction and pneumothorax. The typical disease course displays progressive dyspnea on exertion, spaced by recurrent pneumothoraces and in some patients, chylous pleural effusions or ascites.Most people have dyspnea on exertion with daily activities by 10 years after symptom onset. Many patients require supplemental oxygen over that interval. Genetics
LAM occurs in two settings: in the disease tuberous sclerosis complex (TSC-LAM) and in a sporadic form, in women who do not have TSC (sporadic LAM). In both settings, genetic evidence indicates that LAM is caused by inactivating or “loss of function” mutations in the TSC1 or TSC2 genes, which were cloned in 1997 and 1993 respectively. The TSC1 gene is located on the long arm of chromosome 9 (9q34) and the TSC2 gene is located on the short arm of chromosome 16 (16p13). TSC-LAM occurs in women who have germline mutations in either the TSC1 or the TSC2 gene.Sporadic LAM is primarily associated with somatic TSC2 gene mutations. Germline and somatic mutations in LAM include many types of mutations spread across the genes, with no clear “hot spots,” including missense changes, in-frame deletions and nonsense mutations. Because of the large size of the genes (together they have more than 60 exons) and because mutations can be located virtually anywhere within the genes, mutation detection is often challenging.On a cellular basis, LAM cells carry bi-allelic inactivation of the TSC2 genes, consistent with the “two-hit” tumor suppressor gene model.
Treatment
An FDA-approved drug for treatment of LAM, the mTOR inhibitor sirolimus, is available for stabilization of lung function decline. Lung transplant remains the last resort for patients with advanced disease. Pneumothorax
Pneumothoraces in LAM patients tend to recur, especially after conservative management such as observation, aspiration or simple tube thoracostomy. Over 65% of LAM patients develop pneumothorax during the course of their illness, averaging 3.5 pneumothoraces in those who have at least one pneumothorax. The LAM Foundation Pleural Consensus Group advocated the use of a pleural symphysis procedure with the first pneumothorax, given the greater than 70% chance of recurrence. Chemical sclerosis, mechanical abrasion, talc poudrage and pleurectomy have been effective in patients with LAM, but mechanical abrasion is preferred for those who may require pulmonary transplantation in the future. About half of LAM patients who have undergone transplant have had a prior pleurodesis procedure, and more than 75% of those had had prior bilateral pleurodesis. Although pleurodesis is not a contraindication to transplantation, it can result in increased perioperative bleeding. Chylothorax
Chyle does not generally cause pleural inflammation or fibrosis. Small stable chylous effusions rarely require intervention once the LAM diagnosis is made. Shortness of breath may mandate possibly repeated drainage. Sirolimus is effective for chylous effusions and most experts believe it should be used as the first line of therapy. Imaging the source of the leak with heavy T2-weighted MRI or contrast lymphangiography is an advised for refractory effusions. Some leaks are amenable to embolization through catheters threaded from groin lymph nodes into the thoracic duct.