Multifocal Micronodular Pneumocyte Hyperplasia in Tuberous Sclerosis Complex: Resolution with Everolimus Treatment

[Genetic diffuse cystic lung disease in adults]

Multiple cystic lung diseases comprise a wide range of various diseases, some of them of genetic origin. Lymphangioleiomyomatosis (LAM) is a disease occurring almost exclusively in women, sporadically or in association with tuberous sclerosis complex (TSC). Patients with LAM present with lymphatic complications, renal angiomyolipomas and cystic lung disease responsible for spontaneous pneumothoraces and progressive respiratory insufficiency. TSC and LAM have been ascribed to mutations in TSC1 or TSC2 genes. Patients with TSC are variably affected by cutaneous, cognitive and neuropsychiatric manifestations, epilepsy, cerebral and renal tumors, usually of benign nature. Birt-Hogg-Dubé syndrome is caused by mutations in FLCN encoding folliculin. This syndrome includes lung cysts of basal predominance, cutaneous fibrofolliculomas and various renal tumors. The main complications are spontaneous pneumothoraces and renal tumors requiring systematic screening. The mammalian target of rapamycin (mTOR) pathway is involved in the pathophysiology of TSC, sporadic LAM and Birt-Hogg-Dubé syndrome. MTOR inhibitors are used in LAM and in TSC while Birt-Hogg-Dubé syndrome does not progress towards chronic respiratory failure. Future challenges in these often under-recognized diseases include the need to reduce the delay to diagnosis, and to develop potentially curative treatments. In France, physicians can seek help from the network of reference centers for the diagnosis and management of rare pulmonary diseases.

Perfect match: mTOR inhibitors and tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant syndrome that presents with diverse and complex clinical features and involves multiple human systems. TSC-related neurological abnormalities and organ dysfunction greatly affect the quality of life and can even result in death in patients with TSC. It is widely accepted that most TSC-related clinical manifestations are associated with hyperactivation of the mammalian target of rapamycin (mTOR) pathway caused by loss‑of‑function mutations in TSC1 or TSC2. Remarkable progress in basic and translational research has led to encouraging clinical advances. Although mTOR inhibitors (rapamycin/everolimus) demonstrate great potential in TSC management, two major concerns hamper their generalized application. One is the frequent manifestation of adverse events, such as stomatitis, infections, and menstrual disorders; and the other is the poor response in certain patients. Thus, indicators are required to effectively predict the efficacy of mTOR inhibitors. Herein, we have summarized the current utilization of mTOR inhibitors in the treatment of TSC and focused on their efficacy and safety, in an attempt to provide a reference to guide the treatment of TSC.

Hyperactivation of mammalian target of rapamycin (mTOR) is essential in the pathogenesis of tuberous sclerosis complex (TSC) and can serve as a therapeutic target.

mTOR inhibitors have shown considerable success in multiple clinical trials for the treatment of TSC, including neurological, pulmonary, cardiac, renal, and cutaneous phenotypes.

mTOR inhibitors are associated with adverse events, which should be considered during the management of TSC.

Indicators to predict mTOR inhibitor efficacy are required to select patients who are likely to benefit from such therapy.

Resolution of multifocal micronodular pneumocyte hyperplasia with everolimus in a patient with tuberous sclerosis complex

A woman with a diagnosis of tuberous sclerosis complex (TSC) presented with TSC2 gene mutation and various manifestations, including epilepsy, renal angiomyolipomas (AML), and pathologically confirmed multifocal micronodular pneumocyte hyperplasia (MMPH). With oral administration of everolimus, a mammalian target of rapamycin (mTOR) inhibitor, MMPH and AML were markedly reduced. Further, after starting treatment with everolimus, serum levels of surfactant protein (SP)-A and SP-D, which reflect type II pneumocyte hyperplasia, decreased to the normal range. At the time of writing of this manuscript, 6 years after starting everolimus, MMPH lesions did not relapse and SP-A/D remained the low levels. This is the first case of everolimus efficacy shown for histologically confirmed MMPH in genetically determined TSC patient, with time course of serum SP-A and SP-D.

Tuberous sclerosis complex for the pulmonologist

Tuberous sclerosis complex (TSC) is a rare multisystem genetic disorder affecting almost all organs with no sex predominance. TSC has an autosomal-dominant inheritance and is caused by a heterozygous mutation in either the TSC1 or TSC2 gene leading to hyperactivation of the mammalian target of rapamycin (mTOR). TSC is associated with several pulmonary manifestations including lymphangioleiomyomatosis (LAM), multifocal micronodular pneumocyte hyperplasia (MMPH) and chylous effusions. LAM is a multisystem disorder characterised by cystic destruction of lung parenchyma, and may occur in either the setting of TSC (TSC-LAM) or sporadically (S-LAM). LAM occurs in 30–40% of adult females with TSC at childbearing age and is considered a nonmalignant metastatic neoplasm of unknown origin. TSC-LAM is generally milder and, unlike S-LAM, may occur in males. It manifests as multiple, bilateral, diffuse and thin-walled cysts with normal intervening lung parenchyma on chest computed tomography. LAM is complicated by spontaneous pneumothoraces in up to 70% of patients, with a high recurrence rate. mTOR inhibitors are the treatment of choice for LAM with moderately impaired lung function or chylous effusion. MMPH, manifesting as multiple solid and ground-glass nodules on high-resolution computed tomography, is usually harmless with no need for treatment.

Tuberous sclerosis complex is associated with diverse pulmonary manifestations including LAM, multiple micronodular pneumocyte hyperplasia and chylous effusions. LAM occurs in 30–40% of adult females with tuberous sclerosis complex.https://bit.ly/3iLqZ08

Effect of everolimus on multifocal micronodular pneumocyte hyperplasia in tuberous sclerosis complex

Multifocal micronodular pneumocyte hyperplasia (MMPH) is a benign proliferation of alveolar type II cells presenting as multiple pulmonary nodules at chest imaging, which is frequently seen in patients with tuberous sclerosis complex (TSC). We report a case of a woman with TSC and MMPH who received everolimus, a mechanistic target of rapamycin (mTOR) inhibitor, for the treatment of a subependymal giant cell astrocytoma (SEGA). After 3 months of therapy, a remarkable decrease in density of all pulmonary MMPH lesions was observed, without any change in size. This shows that everolimus is active on MMPH similarly to its effects on SEGA, renal angiomyolipomas, and pulmonary lymphangioleiomyomatosis in TSC, and suggests that the dysregulated activation of mTOR which characterizes TSC also plays a role in the pathogenesis of MMPH.