Last revised by Liz Silverstone on 27 Mar 2024

Lymphangioleiomyomatosis (LAM) is a low-grade destructive metastasizing PEComatous tumor 1 resulting from the proliferation of LAM cells in the lung, kidney and axial lymphatics. The disease is caused by mutations of the TSC2 or TSC1 genes and is more commonly sporadic rather than inherited. Cystic lung disease (CLD) is the most frequent manifestation.

Symptomatic CLD almost exclusively affects women and is associated with sporadic lymphangioleiomyomatosis (s-LAM) or tuberous sclerosis complex (TSC-LAM). The few cases of cystic LAM lung disease in men are associated with TSC-LAM except for one reported case of s-LAM. CLD in men is less severe. CLD may be detected through screening of known TSC cases, but in s-LAM diagnosis is more likely to be delayed and advanced cystic lung destruction may be mistaken for emphysema.

s-LAM may be a forme fruste of TSC. In s-LAM, the mutations are somatic and not heritable, whereas in TSC germline mutations are transmissible to future generations in an autosomal dominant fashion. Even in TSC, sporadic mutations outnumber inherited disease 2:1 and these cases will have a negative family history. TSC affects about 1:6,000 live births. The true prevalence of s-LAM may be as high as 8:1,000,000.

s-LAM can present in late teens or adulthood with lymphatic or lung disease. TSC-LAM commonly presents during childhood with developmental delay, seizures, characteristic skin lesions or tumors. Cystic lung disease and renal angioleiomyoma (AML) are features of both conditions and can present in the following ways:

  • pneumothorax often precedes diagnosis, occurring in >65% of cases and often recurrent, sometimes bilateral

  • pneumothorax during pregnancy

  • progressive dyspnea: the disease is variable, the average age of onset of symptoms is 33 years of age and untreated patients typically become dependent on home oxygen about 10 years afterwards

  • hemoptysis

  • acute abdominal pain and hypovolemic shock due to hemorrhagic renal angiomyolipoma

American Thoracic Society/Japanese Respiratory Society guidelines 2017 2 support a clinical diagnosis of LAM based on typical lung CT and accompanied by any of the following:

TSC is characterized by benign tumors in almost any organ which are frequently detected in childhood or, in the case of cardiac rhabdomyomas, in utero. Children often have developmental delay, seizures and characteristic skin lesions. TSC2 on chromosome 16 codes for tuberin and is more commonly implicated and severe than TSC1 on chromosome 9 which codes for hamartin. Pathological TSC gene mutations are detected in 75-90% of TSC cases 3.

In the absence of a TSC diagnosis, the guidelines recommend testing for vascular endothelial growth factor D (VEGF-D) before resorting to a lung biopsy which must be stained appropriately, including for HMB-45 (other smooth muscle-predominant lesions in the lung do not react with this antibody). VEGF-D levels correlate with the severity of lymphatic involvement and higher levels predict more rapid disease progression and more robust responses to mTOR inhibitors. Serum VEGF-D >800 pg/mL is considered diagnostic. Less severe cases with a normal VEGF-D can be offered transbronchial biopsy which has a diagnostic rate <50%; VATS wedge resection has a higher diagnostic rate but greater morbidity and mortality.

A radiological suspicion without confirmatory findings is insufficient for diagnosis: long-term treatment with sirolimus or everolimus can have serious toxicity, and a wrong diagnosis is a missed opportunity to correctly manage a different condition.

Smooth muscle-like LAM cells contain inactivating mutations of TSC2 or TSC1 tumor suppressor genes with consequent activation of the mechanistic target of rapamycin (mTOR) signaling pathway. This results in proliferation of LAM cells which migrate through lymphatic vessels and infiltrate airways and blood vessels. Lymphatic and vascular obstruction and rupture may result, causing hemorrhage, chylous effusions etc.. The mechanism of cystic lung destruction is uncertain and could involve check-valve obstruction and/or metalloproteinases. LAM cells express estrogen receptors and functional decline accelerates during pregnancy. Estrogen is a driver of LAM cell proliferation and lymphatic dissemination. 

Lung disease, lymphatic disease and chylous leaks predominate in s-LAM, whereas widespread benign tumors and hamartomas are common in TSC. Epithelioid AML may have a relatively aggressive course and is normally rare, but occurs with greater frequency in s-LAM and TSC-LAM.

The source of the LAM cells is not known, however microscopic uterine LAM cell lesions have a high incidence in LAM patients, but are absent in non-LAM controls.

  • large lungs containing scattered thin-walled rounded empty cysts

    • in early disease, the cysts are few and small with normal intervening lung parenchyma

    • the cysts progressively enlarge and become more numerous until there is little normal lung remaining

  • transient areas of increased lung opacity due to hemorrhage

  • small lung nodules representing multifocal micronodular pneumocyte hyperplasia (MMPH) especially in tuberous sclerosis

  • pneumothorax

  • chylous effusions: pleural, pericardial

  • lymphadenopathy

  • dilated thoracic duct

  • myocardial fatty foci in tuberous sclerosis

Best delineated by CT or MRI:

  • single or multiple renal AMLs containing a mixture of fat and soft tissue

    • >90% incidence in TSC cases which have larger and more numerous AMLs compared with about 30% incidence in s-LAM

  • hepatic, adrenal or retroperitoneal AMLs

  • chylous ascites

  • lymphangioleiomyomas: soft cystic/solid masses which can insinuate between normal structures without compressing them. These may be hormone-responsive, waxing and waning through the menstrual cycle 14

  • lymphadenopathy

  • multiple osteoblastic bone lesions in tuberous sclerosis, similar in appearance to enostoses

Median survival is approximately 30 years following diagnosis. There are few medications that have been shown to benefit patients with LAM, with mTOR inhibitors (e.g. sirolimus or everolimus) being one of the main treatment options. mTOR inhibitors limit LAM cell proliferation by inhibiting the activated mTOR pathway, thereby improving lung function, at least in the short-term, and often shrinking masses and chylous effusions. Progression generally resumes on cessation.

​Other potential therapies, depending on the manifestations include:

  • bronchodilators, response seen in ~20% 

  • VATS pleurodesis for recurrent pneumothorax, the method affects perioperative hemorrhage at transplantation

  • lung transplantation for respiratory failure

    • recurrent LAM in transplanted lungs carries the original tuberous sclerosis mutation

  • embolization or nephron-sparing surgery for large, rapidly growing or hemorrhagic AMLs

  • surgery is contraindicated for lymphatic masses, as it can result in persistent chyle leaks

  • genetic counseling for TSC cases

  • pneumococcus and influenza vaccines are advised

Lutembacher's 1918 report described a cystic lung disease associated with tuberous sclerosis complex (TSC) for the first time 12. Von Stössel reported the first known case of sporadic lymphangioleiomyomatosis (LAM) in 1937 12.

  • emphysema

    • advanced emphysema can appear similar to advanced cystic lung disease in LAM

    • fibrosis may mimic cyst walls

    • emphysema distribution depends on etiology

    • LAM will have typical cysts separated by normal parenchyma in the least affected areas

  • lymphocytic interstitial pneumonitis (LIP)

    • in women of child-bearing age, LIP is usually associated with connective tissue disease, especially Sjögren syndrome

    • a smaller number of lower zone predominant perivascular cysts, some with internal soft-tissue may coexist with nodules, ground-glass opacity,  tree-in-bud opacities, lymphoma or amyloid deposits

    • lung changes may pre-date typical serological abnormalities, delaying diagnosis

  • pulmonary Langerhans cell histiocytosis

    • upper zone predominant and bronchocentric cavitating nodules, branching or irregular cysts

    • spares costophrenic and costomediastinal angles

    • typically a disease of young adult smokers, especially men

  • Birt-Hogg-Dubé syndrome

    • fewer cysts with characteristic subpleural distribution and characteristic cyst shapes

    • autosomal dominant inheritance

    • family history of pneumothorax or renal tumors

    • characteristic skin lesions

    • folliculin gene mutation

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