Lymphangioleiomyomatosis, usually shortened to LAM, is a rare lung disease in which abnormal smooth muscle-like cells proliferate throughout the lungs, gradually destroying healthy tissue and replacing it with thin-walled cysts. It overwhelmingly affects women of childbearing age and can occur on its own (sporadic LAM) or alongside a genetic condition called tuberous sclerosis complex (TSC-LAM). Although once considered uniformly progressive and fatal, LAM now has a targeted drug treatment that can stabilize lung function for years, fundamentally changing the outlook for most patients.
What Happens Inside the Lungs
LAM cells look like immature smooth muscle cells, but they behave more like slow-moving cancer. They multiply, migrate, and embed themselves in lung tissue in a disorganized way, quite unlike the orderly layers of smooth muscle found in normal airways and blood vessels.1PubMed Central. Smooth muscle-like cells in pulmonary lymphangioleiomyomatosis These cells are now formally classified as a low-grade malignant soft-tissue tumor belonging to the family of perivascular epithelioid cell tumors (PEComas).2PubMed. Cathepsin K is Superior to HMB45 for the Diagnosis of Pulmonary Lymphangioleiomyomatosis As they grow, they choke off small airways and lymphatic channels, and the surrounding lung tissue breaks down into fluid-filled cysts. Over time the lungs can become riddled with hundreds of these cysts, leading to progressive shortness of breath, reduced oxygen levels, and a high risk of collapsed lung.
The Genetic Root
Whether LAM arises on its own or with tuberous sclerosis, the molecular culprit is the same: mutations that knock out both copies of either the TSC1 or TSC2 gene in LAM cells.3European Respiratory Review. Towards personalised therapy for lymphangioleiomyomatosis: lessons from cancer These genes normally act as brakes on a cellular growth-signaling pathway called mTOR complex 1 (mTORC1). When the brakes are gone, mTORC1 stays switched on, telling cells to keep growing and dividing when they should not be.4JCI Insight. Lymphangioleiomyomatosis — a wolf in sheep’s clothing In sporadic LAM the mutations happen only inside the LAM cells themselves, so they are not inherited. In TSC-LAM, a person inherits one faulty copy of a TSC gene in every cell; a second “hit” in certain cells then tips the balance toward unchecked growth.
Why It Almost Exclusively Affects Women
One of the most striking features of LAM is its near-total restriction to women, and estrogen is the key reason. LAM cells carry estrogen and progesterone receptors, and lung function tends to decline during periods when circulating estrogen is high.5PubMed Central. Minireview: Lymphangioleiomyomatosis (LAM): The “Other” Steroid-Sensitive Cancer Laboratory work using cells taken from LAM patients shows that estrogen drives a strong activation of a secondary signaling pathway (ERK2) that cooperates with the already-overactive mTOR pathway. Together, the two pathways ramp up production of proteins associated with cell movement and invasion.6PubMed Central. Integration of mTOR and estrogen-ERK2 signaling in lymphangioleiomyomatosis pathogenesis This dual-fuel arrangement helps explain why LAM is rarely diagnosed before puberty or after menopause, and why pregnancy can accelerate the disease.
Pregnancy and LAM
Because LAM typically strikes premenopausal women, questions about pregnancy come up often. The rising estrogen levels of pregnancy can unmask previously silent LAM or speed up existing disease.7PubMed Central. Systematic Review of Lymphangioleiomyomatosis Outcomes in Pregnancy and a Proposed Management Guideline Patients first diagnosed during pregnancy tend to have worse outcomes than those diagnosed before conception.8PubMed Central. Lymphangioleiomyomatosis and pregnancy: a mini-review For this reason, women with LAM have historically been counseled to avoid pregnancy. That advice is becoming more nuanced now that mTOR-targeted drugs can control disease activity, but the decision still requires careful discussion with a specialist, especially regarding medication timing and monitoring.
How LAM Shows Up on Imaging
High-resolution CT of the chest is the cornerstone of LAM diagnosis. The hallmark finding is numerous thin-walled, round cysts scattered evenly through both lungs, from top to bottom, ranging from a few millimeters to several centimeters across.9PubMed. Pulmonary lymphangioleiomyomatosis. High-resolution CT findings in 11 patients and compared with the literature Unlike the cysts seen in emphysema, which tend to cluster in the upper lungs and have irregular shapes, LAM cysts are distinctly round and distributed throughout the entire lung, including the bases.10PubMed. Lymphangioleiomyomatosis: pulmonary and abdominal findings with pathologic correlation Researchers have also found that the lung tissue between the cysts is not entirely normal either: subtle changes resembling emphysema were identified in lung tissue of the majority of patients in one imaging study, suggesting that the disease’s impact extends beyond the visible cysts.11PubMed Central. CT grading of lung disease in lymphangioleiomyomatosis
In a woman of childbearing age with this characteristic CT pattern, a clinician can often make the diagnosis without a lung biopsy, especially if certain other features are present. However, other rare cystic lung diseases can mimic LAM on imaging, so additional information is usually needed to confirm the diagnosis.
The VEGF-D Blood Test
One of the most useful advances in LAM diagnosis is a simple blood test measuring vascular endothelial growth factor D (VEGF-D). LAM cells produce unusually large amounts of this protein, which promotes the growth of lymphatic vessels. In a prospective study, a VEGF-D level above 800 pg/mL was essentially diagnostic of LAM, while every patient ultimately found to have a different cystic lung disease had levels below 600 pg/mL.12PubMed Central. Serum vascular endothelial growth factor-D prospectively distinguishes lymphangioleiomyomatosis from other diseases This means that for many patients, a combination of a characteristic CT scan and an elevated VEGF-D level can confirm the diagnosis without surgery.
VEGF-D is also useful as a disease-activity marker. Higher levels correlate with worse airflow obstruction and greater need for supplemental oxygen, while patients who respond to treatment tend to see their levels drop.13The Lancet Respiratory Medicine. Serum vascular endothelial growth factor-D and disease severity and treatment response in lymphangioleiomyomatosis It is not a perfect crystal ball, though: roughly a fifth of patients with sporadic LAM have VEGF-D levels below the diagnostic threshold, so a normal result does not rule out the disease.
Telling LAM Apart from Other Cystic Lung Diseases
Several other rare diseases can fill the lungs with cysts, including Birt-Hogg-Dubé syndrome (BHD), pulmonary Langerhans cell histiocytosis (LCH), and lymphoid interstitial pneumonia (LIP). A recent analysis comparing these conditions found that certain clinical features can sharply narrow the possibilities. Pneumothorax was the first sign of disease in about 90% of BHD patients and roughly a third of LAM patients but did not occur in LIP or LCH. Meanwhile, lymphatic involvement (enlarged lymph nodes, lymphatic masses, or chylous fluid collections) and kidney tumors called angiomyolipomas appeared only in LAM, never in the other conditions.14Annals of the American Thoracic Society. Utility of Presenting Features to Differentiate between Rare Cystic Lung Diseases When these distinguishing features are combined with CT patterns and the VEGF-D blood test, clinicians can usually reach a confident diagnosis without invasive biopsy.
Beyond the Lungs
LAM is not solely a lung disease. It frequently involves the lymphatic system and the kidneys, and understanding these extrapulmonary features matters both for diagnosis and for long-term management.
Kidney Angiomyolipomas
About half of patients with sporadic LAM harbor at least one angiomyolipoma, a benign kidney tumor made of fat, smooth muscle, and abnormal blood vessels. In TSC-LAM the proportion is even higher. A long-term study found that these tumors grew at an average rate of about 2 mm per year, and a number of patients with sporadic LAM eventually needed a kidney removed because of life-threatening bleeding.15PubMed Central. Natural history of angiomyolipoma in lymphangioleiomyomatosis: implications for screening and surveillance Hemorrhage is the chief clinical concern with these tumors, especially once they grow beyond about 4 cm in diameter.16PubMed Central. Evidence-based protocol-led management of renal angiomyolipoma: A review of literature Regular abdominal imaging is recommended so that growing tumors can be treated proactively, often with arterial embolization rather than surgery, to preserve as much kidney tissue as possible.
Lymphatic Problems and Chylous Effusions
LAM cells produce high levels of lymphatic growth factors (VEGF-C and VEGF-D), which stimulate the formation of abnormal lymphatic vessels within and around LAM nodules.17PubMed. Lymphangioleiomyomatosis: a disease involving the lymphatic system When these disordered lymphatics leak, the result is a chylous effusion, a milky fluid collection in the chest or abdomen. In one long-running series at a single center, roughly one in ten LAM patients developed a chylous pleural effusion. Management ranged from simple drainage to surgical procedures like thoracic duct ligation or pleurodesis, depending on severity.18PubMed. Chylothorax in lymphangioleiomyomatosis Clusters of LAM cells have also been observed floating in chylous fluid and within lymphatic channels, which is part of the reason LAM behaves more like a metastasizing tumor than a simple overgrowth.
Sirolimus and the mTOR Revolution
The discovery that LAM is driven by an overactive mTOR pathway made a targeted treatment possible. Sirolimus (rapamycin), a drug originally developed to prevent organ transplant rejection, directly inhibits mTORC1. The landmark trial enrolled 89 women and showed that patients on sirolimus had stable lung function over 12 months, while the placebo group lost about 12 mL of lung capacity per month. The absolute difference was about 153 mL, or roughly 11% of the average starting lung function. Sirolimus also improved quality of life, exercise capacity, and brought down VEGF-D levels.19PubMed Central. Efficacy and Safety of Sirolimus in Lymphangioleiomyomatosis
Long-term observational studies have since confirmed that these benefits hold up over years of treatment, with lung function, oxygen needs, and quality of life all remaining stable or improving over four-year follow-up periods.20PubMed Central. Long-term efficacy and safety of sirolimus therapy in patients with lymphangioleiomyomatosis However, sirolimus does not cure LAM. The disease tends to progress again if the drug is stopped, which means most patients face the prospect of lifelong treatment.
Side Effects of Long-Term Sirolimus
Because sirolimus suppresses part of the immune system, it carries real side effects. In one single-center series following 48 patients, about a third experienced side effects. The most common was mouth ulcers, affecting roughly one in six patients. Other reported problems included ovarian cysts, elevated cholesterol, liver enzyme abnormalities, and fluid retention, though only one patient in that cohort had to stop the drug entirely.21PubMed Central. Long-term results of sirolimus treatment in lymphangioleiomyomatosis: a single referral centre experience Side effects tend to be worst in the early months and settle over time. Doctors monitor blood levels of the drug along with cholesterol, kidney function, and blood counts at regular intervals. Infections are a concern with any immunosuppressant, so patients on sirolimus need to be vigilant about vaccinations and prompt treatment of infections.
Managing Pneumothorax
Collapsed lung is one of the most common and disruptive complications of LAM. Pooled data suggest that more than half of LAM patients will experience at least one pneumothorax, and recurrence rates are punishing: most estimates hover around 70%, with affected patients averaging three to five episodes each.22American Journal of Respiratory and Critical Care Medicine. Lymphangioleiomyomatosis Diagnosis and Management: High-Resolution Chest Computed Tomography, Transbronchial Lung Biopsy, and Pleural Disease Management These repeated collapses mean hospitalizations, chest tubes, lost work, and considerable anxiety.
For this reason, the American Thoracic Society and Japanese Respiratory Society guidelines recommend pleurodesis (a procedure that seals the lung to the chest wall) after the very first pneumothorax rather than waiting for it to happen again. Patients managed conservatively after a first episode had a recurrence rate around 65%, compared with roughly 18 to 32% after pleurodesis. The trade-off is that pleurodesis can complicate a future lung transplant by making surgery technically harder, but because most patients will eventually need the procedure anyway, the panel concluded it is better to do it sooner. An alternative approach used at some centers is total pleural covering (TPC), a surgical technique that wraps the lung surface in a sheet of absorbable material. In one series, about three-quarters of treated lung sides remained free of further pneumothorax, with the probability of staying recurrence-free estimated at roughly 72% at five years.23PLoS ONE. A Total Pleural Covering for Lymphangioleiomyomatosis Prevents Pneumothorax Recurrence
When Transplant Becomes the Option
For patients whose lung function deteriorates despite sirolimus, bilateral lung transplantation is the last resort. Survival data from transplant centers vary somewhat but generally fall in the range of 60 to 77% at five years and 46 to 58% at ten years.24The Journal of Heart and Lung Transplantation. Lung transplantation in lymphangioleiomyomatosis: Results and influence of sirolimus therapy 25CHEST. Outcomes and recurrence of disease after lung transplantation in advanced LAM These numbers are broadly comparable to transplant outcomes for other lung diseases, which is encouraging.
One unusual concern is that LAM can recur in the transplanted lungs. Because LAM cells behave like a metastatic neoplasm and can circulate through the lymphatic system and bloodstream, they can seed new grafts. In one documented case, recurrence appeared nine years after bilateral transplantation.26PubMed Central. Recurrence of lymphangioleiomyomatosis: Nine years after a bilateral lung transplantation Recurrence rates are low overall, and when it does happen, switching the patient’s immunosuppressive regimen to include sirolimus can control the regrowth. Still, the possibility of recurrence is something transplant teams discuss with patients beforehand.
Exercise and Pulmonary Rehabilitation
Living with LAM means living with reduced lung capacity, and many patients assume they should limit physical activity. Research suggests the opposite. A systematic review of physiotherapy studies in LAM found that programs combining endurance and resistance training improved lung function, exercise tolerance, depression symptoms, and quality of life.27PubMed Central. Physiotherapy in lymphangioleiomyomatosis: a systematic review A separate study looked at a four-week inpatient pulmonary rehabilitation program in 58 patients with advanced LAM whose lung function averaged only about 45% of predicted. After the program, their six-minute walking distance increased by an average of 49 meters and their quality-of-life scores improved significantly, with gains comparable to those seen in patients with COPD going through the same program.28PubMed Central. Benefits of pulmonary rehabilitation in patients with advanced lymphangioleiomyomatosis (LAM) compared with COPD – a retrospective analysis No clinical baseline characteristics predicted who would benefit most, meaning even patients with quite severe disease saw improvements.
Emerging Treatment Strategies
Sirolimus was a breakthrough, but it does not eliminate LAM cells; it mainly keeps them in check. Researchers are looking for combinations that could do more. One approach under investigation adds hydroxychloroquine, a drug that blocks a cellular recycling process called autophagy. The idea is that when sirolimus starves LAM cells of growth signals, they survive by cannibalizing their own components through autophagy. Blocking that escape route might push the cells toward death. An early-phase safety trial combining sirolimus with hydroxychloroquine in 13 patients found the combination was well tolerated and lung function improved over 24 weeks, though it declined again once treatment was stopped.29PubMed Central. Novel treatment strategies for lymphangioleiomyomatosis: a narrative review The cooperation between the mTOR pathway and estrogen signaling is also a therapeutic target: laboratory work has shown that blocking both pathways simultaneously may be more effective than hitting either one alone.30PubMed Central. Integration of mTOR and estrogen-ERK2 signaling in lymphangioleiomyomatosis pathogenesis Clinical trials testing anti-estrogen strategies in combination with mTOR inhibitors have yet to deliver results, but the rationale is strong enough to keep the approach alive.
Sporadic LAM Versus TSC-LAM
Most patients with LAM have the sporadic form, meaning they do not have tuberous sclerosis. In a national center audit of TSC-LAM patients, baseline lung function measures were remarkably similar between the two groups, with both showing reduced airflow and gas transfer at the time of first clinical assessment.31PubMed Central. Lymphangioleiomyomatosis in patients with tuberous sclerosis: a national centre audit CT imaging studies have compared the two forms and generally find the same cystic pattern, though TSC-LAM patients tend to be diagnosed slightly younger (mean age around 40 versus 44 for sporadic LAM in one series) and may have additional TSC-related findings like skin lesions or brain tumors.32PubMed Central. Sporadic Lymphangioleiomyomatosis and Tuberous Sclerosis Complex with Lymphangioleiomyomatosis: Comparison of CT Features From a treatment standpoint, sirolimus works in both forms, which makes sense given that both share the same mTOR-driven mechanism. The practical difference is that TSC-LAM patients need surveillance for the many other organ systems that tuberous sclerosis can affect, including the brain, kidneys, skin, and heart.
One diagnostic subtlety: VEGF-D levels tend to be higher in TSC-LAM than in sporadic LAM, with median values roughly two to three times greater in some cohorts.33PubMed Central. Serum vascular endothelial growth factor-D prospectively distinguishes lymphangioleiomyomatosis from other diseases This can be useful for screening women with TSC who have no lung symptoms yet, since an elevated VEGF-D level may prompt earlier CT imaging and earlier detection of cystic change before lung function is lost.