Characterization of pulmonary cysts in Birt-Hogg-Dubé syndrome: histopathological and morphometric analysis of 229 pulmonary cysts from 50 unrelated patients

Diffuse Cystic Lung Disease: A Clinical Guide to Recognition and Management

TOPIC IMPORTANCE

Diffuse cystic lung diseases (DCLDs) represent a group of pathophysiologically heterogeneous entities that share a common radiologic phenotype of multiple thin-walled pulmonary cysts. DCLDs differ from the typical fibroinflammatory interstitial lung diseases in their epidemiology, clinical presentation, molecular pathogenesis, and therapeutic approaches, making them worthy of a distinct classification. The importance of timely and accurate identification of DCLDs is heightened by the impact on patient management including recent discoveries of targeted therapeutic approaches for some disorders.

REVIEW FINDINGS

This article offers a practical framework for evaluating patients with DCLD, indicating the most appropriate and current diagnostic and management approaches. We focus on the DCLDs that are most likely to be encountered by practicing pulmonologists: lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, Birt-Hogg-Dubé syndrome, and lymphoid interstitial pneumonia. Chest CT scan is the most informative noninvasive diagnostic modality to identify DCLDs. Thereafter, instituting a structured approach to high-yield associated factors (eg, medical, social, and family history; renal and dermatologic findings) increases the likelihood of identifying DCLDs and achieving a diagnosis.

SUMMARY

Although the individual diseases that comprise the DCLD family are rare, taken together, DCLDs can be encountered more frequently in clinical practice than commonly perceived. An increased eagerness among general pulmonary physicians to recognize these entities, coupled with a practical and systematic clinical approach to examinations and investigations, is required to improve case findings, allow earlier intervention, and reduce morbidity and mortality.

Birt-Hogg-Dubé syndrome in an overall view: Focus on the clinicopathological prospects in renal tumors

Birt-Hogg-Dubé syndrome (BHD) represents a rare autosomal dominant tumor predisposition syndrome characterized by skin lesions, lung cysts, and renal tumors. The predominant histological subtypes of BHD-related renal tumors include hybrid oncocytoma-chromophobe tumors, oncocytomas, and chromophobe renal cell carcinomas, all exhibiting eosinophilic/oncocytic features. Immunohistochemistry staining for KIT (CD117) and CK7 exhibits variability in these tumor types. Germline mutations in FLCN have been consistently identified. Generally, patients with BHD demonstrate a favorable prognosis with minimal metastatic potential. Nonetheless, the comprehensive elucidation of pathological characteristics of BHD remains incomplete, particularly in BHD-associated renal tumors that deviate from the previously identified subtypes, thereby complicating the differential diagnosis. In this review, we provide a comprehensive overview of BHD encompassing epidemiology, clinical manifestations, genetic and molecular pathogenesis, as well as clinical diagnostic modalities. Emphasis is placed on clinicopathological features, specifically focusing on BHD-associated renal tumors. Collectively, this review aims to present the latest insights into BHD which benefits in the early detection, therapeutic decision-making, and prognosis prediction in BHD cases, and deepen the understanding of sporadic renal tumors.

Diagnosis of cystic lung diseases: a position statement from the UK Cystic Lung Disease Rare Disease Collaborative Network

BACKGROUND

Rare cystic lung diseases are increasingly recognised due the wider application of CT scanning making cystic lung disease management a growing part of respiratory care. Cystic lung diseases tend to have extrapulmonary features that can both be diagnostic but also require surveillance and treatment in their own right. As some of these diseases now have specific treatments, making a precise diagnosis is crucial. While Langerhans cell histiocytosis, Birt-Hogg-Dubé syndrome, lymphoid interstitial pneumonia and lymphangioleiomyomatosis are becoming relatively well-known diseases to respiratory physicians, a targeted and thorough workup improves diagnostic accuracy and may suggest other ultrarare diseases such as light chain deposition disease, cystic pulmonary amyloidosis, low-grade metastatic neoplasms or infections. In many cases, diagnostic information is overlooked leaving uncertainty over the disease course and treatments.

AIMS

This position statement from the Rare Disease Collaborative Network for cystic lung diseases will review how clinical, radiological and physiological features can be used to differentiate between these diseases.

NARRATIVE

We highlight that in many cases a multidisciplinary diagnosis can be made without the need for lung biopsy and discuss where tissue sampling is necessary when non-invasive methods leave diagnostic doubt. We suggest an initial workup focusing on points in the history which identify key disease features, underlying systemic and familial diseases and a clinical examination to search for connective tissue disease and features of genetic causes of lung cysts. All patients should have a CT of the thorax and abdomen to characterise the pattern and burden of lung cysts and extrapulmonary features and also spirometry, gas transfer and a 6 min walk test. Discussion with a rare cystic lung disease centre is suggested before a surgical biopsy is undertaken.

CONCLUSIONS

We suggest that this focused workup should be performed in all people with multiple lung cysts and would streamline referral pathways, help guide early treatment, management decisions, improve patient experience and reduce overall care costs. It could also potentially catalyse a national research database to describe these less well-understood and unidentified diseases, categorise disease phenotypes and outcomes, potentially leading to better prognostic data and generating a stronger platform to understand specific disease biology.

Pulmonary interstitial glycogenosis in Birt-Hogg-Dubé syndrome-associated lung cysts: A new insight into the pathogenesis?

Multiple lung cysts are one of the major features of Birt-Hogg-Dubé syndrome (BHD), but little is known about their nature and pathogenesis. We report a case of a woman diagnosed with BHD lung cysts who exhibited pulmonary interstitial glycogenosis (PIG), a mesenchymal abnormality hitherto undescribed in this disease, in specimens resected at 14 and 29 years of age. Histopathologically, oval to spindle clear cells were seen in the subepithelial interstitial tissue of septal structures and the walls of the cysts. They had abundant periodic acid-Schiff-positive cytoplasmic glycogen. Immunohistochemically, these cells were positive for a few markers of mesenchymal stem cell-like lineage, including vimentin, CD44, and CD10, and negative for markers of epithelial or specific mesenchymal differentiation; these results were consistent with the reported immunophenotype of PIG cells. These PIG cells were more abundant in her specimen at age 14 years than in the second specimen from adulthood. The present case suggests that BHD lung cysts belong to a group of pulmonary developmental disorders characterized by combined PIG and alveolar simplification/cystic change. Disorders with PIG may persist until adulthood and may be of clinical and pathological significance.

Progression of pulmonary cysts in Birt-Hogg-Dubé syndrome: longitudinal thoracic computed tomography study with quantitative assessment

BACKGROUND

Birt-Hogg-Dubé (BHD) syndrome is a rare autosomal dominant disorder characterized by fibrofolliculomas, renal tumors, pulmonary cysts, and recurrent pneumothorax. Pulmonary cysts are the cause of recurrent pneumothorax, which is one of the most important factors influencing patient quality of life. It is unknown whether pulmonary cysts progress with time or influence pulmonary function in patients with BHD syndrome. This study investigated whether pulmonary cysts progress during long-term follow-up (FU) by using thoracic computed tomography (CT) and whether pulmonary function declines during FU. We also evaluated risk factors for pneumothorax in patients with BHD during FU.

METHODS

Our retrospective cohort included 43 patients with BHD (25 women; mean age, 54.2 ± 11.7 years). We evaluated whether cysts progress by visual assessment and quantitative volume analysis using initial and serial thoracic CT. The visual assessment included the size, location, number, shape, distribution, presence of a visible wall, fissural or subpleural cysts, and air-cuff signs. In CT data obtained from a 1-mm section from 17 patients, the quantitative assessment was performed by measuring the volume of the low attenuation area using in-house software. We evaluated whether the pulmonary function declined with time on serial pulmonary function tests (PFT). Risk factors for pneumothorax were analyzed using multiple regression analysis.

RESULTS

On visual assessment, the largest cyst in the right lung showed a significant interval increase in size (1.0 mm/year, p = 0.0015; 95% confidence interval [CI], 0.42-1.64) between the initial and final CT, and the largest cyst in the left lung also showed significant interval increase in size (0.8 mm/year, p < 0.001, 95% CI; -0.49-1.09). On quantitative assessment, cysts had a tendency to gradually increase in size. In 33 patients with available PFT data, FEV1pred%, FEV1/FVC, and VCpred% showed a statistically significant decrease with time (p < 0.0001 for each). A family history of pneumothorax was a risk factor for the development of pneumothorax.

CONCLUSIONS

The size of pulmonary cysts progressed over time in longitudinal follow-up thoracic CT in patients with BHD, and pulmonary function had slightly deteriorated by longitudinal follow-up PFT.

Exons 1-3 deletion in FLCN is associated with increased risk of pneumothorax in Chinese patients with Birt-Hogg-Dubé syndrome

BACKGROUND

The pathogenic variants responsible for Birt-Hogg-Dubé syndrome (BHDS) in folliculin (FLCN) gene mostly consist of point mutations. Although large intragenic deletions/duplications have been reported in several case reports, the relationship between large intragenic deletions/duplications and phenotype in BHDS remains unclear.

METHODS

We retrospectively identified and reviewed patients with a large intragenic deletion spanning exons 1-3 and analyzed their phenotypic features to compare with those of point mutation carriers in our hospital from January 1, 2017 to August 31, 2022.

RESULTS

Twenty unique point mutations (including 4 novel mutations) were detected in 62 patients from 45 families (90%). Exons 1-3 deletion were identified in 8 patients from 5 families (10%) that resided in the same region, Feidong County of Anhui Province, China. Breakpoint analysis indicated that all the deletion breakpoints were flanked by Alu repeats. The prevalence of exons 1-3 deletion carriers in Feidong County was 8.1-times higher than that for BHDS in Anhui Province, suggesting a clustered phenomenon of exons 1-3 deletion. Significantly increased risk of pneumothorax was observed in those with exons 1-3 deletion compared with point mutations (91% vs. 58%, p value 0.047). The risk of renal cancer may be higher in those with exons 1-3 deletion than for those with point mutations (18% vs. 4%, p > 0.05).

CONCLUSIONS

Large intragenic deletion of exons 1-3 in FLCN was identified as a local aggregation phenomenon in Feidong County, China, and was associated with a significantly higher risk of pneumothorax compared to those with point mutations.

High-Resolution Computed Tomography of Cystic Lung Disease

The cystic lung diseases (CLD) are characterized by the presence of multiple, thin-walled, air-filled spaces in the pulmonary parenchyma. Cyst formation may occur with congenital, autoimmune, inflammatory, infectious, or neoplastic processes. Recognition of cyst mimics such as emphysema and bronchiectasis is important to prevent diagnostic confusion and unnecessary evaluation. Chest CT can be diagnostic or may guide the workup based on cyst number, distribution, morphology, and associated lung, and extrapulmonary findings. Diffuse CLD (DCLDs) are often considered those presenting with 10 or more cysts. The more commonly encountered DCLDs include lymphangioleiomyomatosis, pulmonary Langerhans' cell histiocytosis, lymphoid interstitial pneumonia, Birt-Hogg-Dubé syndrome, and amyloidosis/light chain deposition disease.

Birt-Hogg-Dubé syndrome in apparent primary spontaneous pneumothorax patients; results and recommendations for clinical practice

Background

Birt-Hogg-Dubé syndrome (BHD) is an inherited disease caused by pathogenic variants in the FLCN gene. One of the characteristics is the increased risk for spontaneous pneumothorax, likely due to the presence of pulmonary cysts mainly distributed under the carina. Due to variable expression and lack of awareness, BHD is likely to be underdiagnosed. We aimed to examine the prevalence of BHD in patients presenting with an apparent primary spontaneous pneumothorax and to evaluate the contribution of chest CT in establishing the diagnosis.

Methods

Patients who presented with apparent primary spontaneous pneumothorax between 2004 and 2017 in a large Dutch teaching hospital were enrolled in this quantitative cross-sectional study. A questionnaire was sent to eligible patients. Patients who completed the questionnaire and consented to further participation were invited to visit the hospital for genetic testing and low dose, volumetric chest CT.

Results

Genetic testing was performed in 88 patients with apparent primary spontaneous pneumothorax. Three patients were found to have a pathogenic variant in the FLCN gene (3.4%). No variants of unknown significance were detected. Pulmonary cysts were detected in 14 out of 83 participants with an available chest CT, six had more than one cyst. All three patients with BHD had multiple pulmonary cysts.

Conclusions

Based on previous literature and the present study, we believe that performing a chest CT in every patient presenting with primary spontaneous pneumothorax is justified. Subsequent genetic testing of the FLCN gene should be considered when multiple pulmonary cysts are present.

Trial registration

The study was registered at clinicaltrials.gov with reference NCT02916992.

Summary at a glance

Three out of 88 patients with an apparent primary spontaneous pneumothorax were diagnosed with Birt-Hogg-Dubé syndrome in this study and all three had multiple pulmonary cysts. We believe that performing a chest CT in every patient with an apparent primary spontaneous pneumothorax is justified to identify underlying diseases.

Birt-Hogg-Dubé syndrome with rare unclassified renal cell carcinoma: A case report

INTRODUCTION

Birt-Hogg-Dubé syndrome (BHDS) is a rare genetic disease. Renal cell carcinoma is the most serious complication of BHDS. The histological types of BHDS-related renal cell carcinoma are mostly mixed chromophobe/eosinophil and chromophobe cell types. BHDS with unclassified renal cell carcinoma is extremely rare.

PATIENT CONCERNS

A 37-year-old man was admitted to the hospital because of lumbago and hematuria.

DIAGNOSIS

Combined with abdominal enhanced CT and pulmonary CT, BHDS complicated with renal cell carcinoma was diagnosed, and right partial nephrectomy was performed. The postoperative pathological diagnosis was unclassified renal cell carcinoma. Gene detection revealed the FLCN frameshift mutation.

OUTCOMES

No signs of recurrence were observed after regular follow-up.

CONCLUSION

The pathogenesis of BHDS has not been fully elucidated, and the pathological type of BHDS with unclassified renal cell carcinoma is extremely rare. Through case presentation and review of related literature, this paper summarizes the diagnosis and treatment of BHDS complicated with unclassified renal cell carcinoma.

Pneumothorax: Classification and Etiology

Pneumothorax is a common problem worldwide. Pneumothorax develops secondary to diverse aetiologies; in many cases, there may be no recognizable lung abnormality. The pathogenetic mechanism(s) causing spontaneous pneumothorax may be related to an interplay between lung-related abnormalities and environmental factors such as smoking. Tobacco smoking is a major risk factor for primary spontaneous pneumothorax; chronic obstructive pulmonary disease is most frequently associated with secondary spontaneous pneumothorax. This review article provides an overview of the historical perspective, epidemiology, classification, and aetiology of pneumothorax. It also aims to highlight current knowledge and understanding of underlying risks and pathophysiological mechanisms in pneumothorax development.

A 44-Year-Old Woman With Multiple Neoplasms and Cystic Lung Disease

CASE PRESENTATION

A 44-year-old woman with a history of renal cell carcinoma and thyroid cancer was referred to our institution for evaluation of cystic lung disease. She was an active smoker with a 15-pack-year of tobacco use. Two years before her presentation, she underwent a left nephrectomy for renal cell carcinoma, clear cell type. Four months before, she had a total thyroidectomy that showed nodules consistent with noninvasive follicular thyroid neoplasm with papillary like nuclear features. She had no previous pulmonary complaints. Her family history was positive for breast cancer in her grandmother. There was no family history of pneumothorax. She complained of mild shortness of breath with exertion and occasional nonproductive cough. As part of her oncologic work up, she underwent a chest CT scan of the lungs (Fig 1).

Birt-Hogg-Dubé syndrome

Birt–Hogg–Dubé syndrome (BHD) is a rare inherited autosomal dominant disorder caused by germline mutations in the tumour suppressor gene FLCN, encoding the protein folliculin. Its clinical expression typically includes multiple pulmonary cysts, recurrent spontaneous pneumothoraces, cutaneous fibrofolliculomas and renal tumours of various histological types. BHD has no sex predilection and tends to manifest in the third or fourth decade of life. Multiple bilateral pulmonary cysts are found on chest computed tomography in >80% of patients and more than half experience one or more episodes of pneumothorax. A family history of pneumothorax is an important clue, which suggests the diagnosis of BHD. Unlike other cystic lung diseases such as lymphangioleiomyomatosis and pulmonary Langerhans cell histiocytosis, BHD does not lead to progressive loss of lung function and chronic respiratory insufficiency. Renal tumours affect about 30% of patients during their lifetime, and can be multiple and recurrent. The diagnosis of BHD is based on a combination of genetic, clinical and/or skin histopathological criteria. Management mainly consists of early pleurodesis in the case of pneumothorax, periodic renal imaging for tumour detection, and diagnostic work-up in search of BHD in relatives of the index patient.

Birt–Hogg–Dubé syndrome is a rare genetic disorder characterised by multiple lung cysts, recurrent pneumothoraces, skin lesions and kidney tumours. As the presenting symptoms may be respiratory, chest physicians should be able to identify this disease.https://bit.ly/2xsOTuk

Ultra-rare cystic disease

Diffuse cystic lung diseases include a group of heterogeneous disorders characterised by the presence of cysts within the lung parenchyma, sometimes showing a characteristic computed tomography scan pattern that allows diagnosis. The pathogenetic mechanisms underlying cyst formation in the lung are still not clear and a number of hypotheses have been postulated according to the different aetiologies: ball-valve effect, ischaemic dilatation of small airways and alveoli related to infiltration and obstruction of small vessels and capillaries that supply the terminal bronchioles and connective tissue degradation by matrix metalloproteases. A wide number of lung cyst diseases have been classified into six diagnostic groups according to the aetiology: neoplastic, congenital/genetic, lymphoproliferative, infective, associated with interstitial lung diseases, and other causes. This article focuses on lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis and Erdheim–Chester disease, Birt–Hogg–Dubé, follicular bronchiolitis and lymphocytic interstitial pneumonia, light-chain deposition disease and amyloidosis, congenital lung disease associated with aberrant lung development and growth, and cystic lung disease associated with neoplastic lesion. These cystic diseases are epidemiologically considered as ultra-rare conditions as they affect fewer than one individual per 50 000 or fewer than 20 individuals per million. Despite the rarity of this group of disorders, the increasing use of high-resolution computed tomography has improved the diagnostic yield, even in asymptomatic patients allowing prompt and correct therapy and management without the need for a biopsy.

Diffuse cystic lung diseases show a characteristic CT scan pattern that often allows for diagnosis, even in asymptomatic patients, allowing prompt correct therapy and management without the needing of a biopsyhttps://bit.ly/2wIUKet

Loss of FLCN inhibits canonical WNT signaling via TFE3

Lower lobe predominant pulmonary cysts occur in up to 90% of patients with Birt-Hogg-Dubé (BHD) syndrome, but the key pathologic cell type and signaling events driving this distinct phenotype remain elusive. Through examination of the LungMAP database, we found that folliculin (FLCN) is highly expressed in neonatal lung mesenchymal cells. Using RNA-Seq, we found that inactivation of Flcn in mouse embryonic fibroblasts leads to changes in multiple Wnt ligands, including a 2.8-fold decrease in Wnt2. This was associated with decreased TCF/LEF activity, a readout of canonical WNT activity, after treatment with a GSK3-α/β inhibitor. Similarly, FLCN deficiency in HEK293T cells decreased WNT pathway activity by 76% post-GSK3-α/β inhibition. Inactivation of FLCN in human fetal lung fibroblasts (MRC-5) led to ~ 100-fold decrease in Wnt2 expression and a 33-fold decrease in Wnt7b expression-two ligands known to be necessary for lung development. Furthermore, canonical WNT activity was decreased by 60%. Classic WNT targets such as AXIN2 and BMP4, and WNT enhanceosome members including TCF4, LEF1 and BCL9 were also decreased after GSK3-α/β inhibition. FLCN-deficient MRC-5 cells failed to upregulate LEF1 in response to GSK3-α/β inhibition. Finally, we found that a constitutively active β-catenin could only partially rescue the decreased WNT activity phenotype seen in FLCN-deficient cells, whereas silencing the transcription factor TFE3 completely reversed this phenotype. In summary, our data establish FLCN as a critical regulator of the WNT pathway via TFE3 and suggest that FLCN-dependent defects in WNT pathway developmental cues may contribute to lung cyst pathogenesis in BHD.

Quantitative Analysis of Cystic Lung Diseases by Use of Paired Inspiratory and Expiratory CT: Estimation of the Extent of Cyst-Airway Communication and Evaluation of Diagnostic Utility

PURPOSE

To establish a method for quantitatively estimating the extent of the communication between the cyst and the airway in cystic lung diseases (CLDs) and evaluate its diagnostic utility in differentiating among CLDs.

MATERIALS AND METHODS

Seventy-one patients (mean age, 49.9 years; age range, 25-79 years) with CLDs who underwent paired inspiratory and expiratory CT between July 2015 and July 2018 were enrolled in this prospective study. Participants were divided into three groups based on their diagnosis: Birt-Hogg-Dubé syndrome (BHDS) group (15 participants), lymphangioleiomyomatosis (LAM) group (43 participants), and other diseases (OT) group (13 participants). Total lung volume (TLV) and low-attenuation area volume (LAAV) were calculated at inspiration and expiration. The collapsibility of the LAAV was determined as the expiration-to-inspiration (E/I) ratio of LAAV (E/I ratio LAAV). The cyst-airway communicating index (CACI), the ratio of the LAAV change between inspiration and expiration to the TLV change between inspiration and expiration, was also determined. Receiver operating characteristic (ROC) analysis was used to evaluate the diagnostic utility for differentiating diseases.

RESULTS

The E/I ratio LAAV was significantly higher in the BHDS group (0.69; 95% confidence interval [CI]: 0.61, 0.78) than in the LAM (0.33; 95% CI: 0.28, 0.38) (P < .001) and the OT (0.51; 95% CI: 0.38, 0.64) (P = .038) groups. The CACI was significantly lower in the BHDS group (0.89; 95% CI: 0.61, 1.17) than in the LAM (1.89; 95% CI: 1.76, 2.0) (P < .001) and the OT (1.539; 95% CI: 1.21, 1.86) (P = .003) groups. There was no significant difference in the area under the ROC curve of the CACI (0.881; 95% CI: 0.7749, 0.987) and the E/I ratio LAAV (0.877; 95% CI: 0.791, 0.963) for differentiating BHDS from other diseases.

CONCLUSION

Quantitative analysis using paired inspiratory and expiratory CT for estimating the extent of cyst-airway communication in CLDs is useful when distinguishing BHDS from other diseases.Supplemental material is available for this article.© RSNA, 2020See also the commentary by Chung in this issue.

Genetic Risk Factors for Spontaneous Pneumothorax in Birt-Hogg-Dubé Syndrome

BACKGROUND

Birt-Hogg-Dubé syndrome (BHDS) is a genetic tumor syndrome characterized by lung cysts, spontaneous pneumothorax, fibrofolliculomas, and renal cell cancer. Because of its rarity and clinical heterogeneity, much is still unknown regarding the course of the disease and individual risk assessment. Therefore, we studied nonenvironmental risk factors for pneumothorax in a large sample of patients with BHDS.

METHODS

Clinical data were available from 197 patients with BHDS (male patients, 103; female patients, 94) belonging to 63 unrelated families. The FLCN coding region including adjacent intronic sequences was analyzed by PCR and subsequent Sanger sequencing as well as by multiplex ligation-dependent probe amplification. Statistical analyses were performed, using adequate methods to account for familial clustering.

RESULTS

Patients who had only a single spontaneous pneumothorax were significantly older at the time of occurrence than those with multiple pneumothoraces (mean, 38.93 vs 29.74 years; P value, .010). The risk for three or more pneumothoraces drastically increased after the second event. Significantly increased pneumothorax risks were found for mutations c.1300G>C (59%) and c.250-2A>G (77%), compared with FLCN hotspot mutation c.1285dup (37% risk) (P value, .02).

CONCLUSIONS

We observed significant differences for the spontaneous pneumothorax risk regarding both age and sex in patients with BHDS. Furthermore, two FLCN mutations were identified that are associated with significantly increased pneumothorax risk. Thus, formerly unknown individual predictors have been identified that provide improved risk stratification for patients with BHDS.

Familial pneumothoraces - Birt-Hogg-Dubé syndrome. Differentiation with other cystic lung diseases

Birt-Hogg-Dubé syndrome (BHDS) is a rare, genetic, autosomal dominant disease caused by mutation in a folliculin gene. This syndrome is characterised by three main symptoms: benign lesions originating from hair follicles, variously shaped cysts in the lungs, and various types of benign and malignant kidney neoplasms. In our article we are going to present cases of two sisters with BHDS. In the case of the first sister skin lesions were accompanied by lung abnormalities. The second sister, however, presented with recurrent pneumothoraces associated with variously shaped lung cysts located mainly below the tracheal carina. In both instance diagnosis was confirmed by genetic test.

Pathology of Birt-Hogg-Dubé syndrome: A special reference of pulmonary manifestations in a Japanese population with a comprehensive analysis and review

Birt-Hogg-Dubé (BHD) syndrome is a rare genetic disorder characterized by cutaneous fibrofolliculomas, pulmonary cysts and renal cell carcinomas. Affected individuals inherit germline mutations in the folliculin gene (FLCN). Approximately 150 pathogenic FLCN variants have been identified worldwide. Many Japanese probands of BHD syndrome were first identified by pulmonologists and/or radiologists during treatment of pneumothoraces. Lung specimens obtained through video-assisted thoracoscopic surgery (VATS) have characteristic features unique to BHD syndrome; however, pathologists often miss key findings and diagnose patients with "bullae/blebs". The pleural and subpleural cysts of BHD syndrome-associated lung diseases are often modified by tissue remodeling and can be difficult to distinguish from emphysematous bullae/blebs. Intraparenchymal unruptured cysts tend to retain distinctive features that are different from other cystic lung diseases. Here, we review the clinicopathological findings of BHD syndrome in a Japanese population based on data from 200 probands diagnosed by genetic testing and a total of 520 symptomatic family members identified through BHD-NET Japan (http://www.bhd-net.jp/). Detailed morphology of pulmonary cysts obtained from VATS and autopsied lung specimens are described, and pathological clues for differentiating miscellaneous cystic lung disorders are discussed.

Pulmonary cysts in smoking-related interstitial fibrosis: a form of pseudocyst secondary to pulmonary interstitial emphysema

Smoking-related interstitial fibrosis is a distinct form of fibrosis, found in smokers, which has striking histopathological features. We present a case of pulmonary interstitial fibrosis with cysts in a 58-year-old woman who was a significant active smoker, presenting with a 7 month history of progressive dyspnea. TAC revealed thin-walled pulmonary cysts. An open lung biopsy was performed and the histopathological study showed hyaline fibrous thickening of the alveolar septa, respiratory bronchiolitis and cysts in the thickness of the interlobar septa. Immunohistochemically, the absence of an epithelial, vascular or lymphatic endothelial lining of the cysts would suggest that the cysts had been caused by pulmonary interstitial emphysema. Immunohistochemistry is essential in the differential diagnosis that includes, in this case, true cysts, pseudocysts and pulmonary lymphangiectasia.

A total pleural covering of absorbable cellulose mesh prevents pneumothorax recurrence in patients with Birt-Hogg-Dubé syndrome

Background

Birt-Hogg-Dubé syndrome (BHDS) is a recently recognized inherited multiple cystic lung disease causing recurrent pneumothoraces. Similarly to the lesions in patients with lymphangioleiomyomatosis (LAM), the pulmonary cysts are innumerable and widely dispersed and cannot all be removed. We recently described a total pleural covering (TPC) that covers the entire visceral pleura with oxidized regenerated cellulose (ORC) mesh. TPC successfully prevented the recurrence of pneumothorax in LAM patients. The purpose of this study was to evaluate the effect of an ORC pleural covering on pneumothorax recurrence in BHDS patients.

Results

This retrospective study enrolled a total of 81 pneumothorax patients with the diagnosis of BHDS who underwent 90 covering surgeries from January 2010 to August 2017 at Tamagawa Hospital. During the first half of the study period, a lower pleural covering (LPC) which covered the affected area with ORC mesh was mainly used to treat 38 pneumothoraces. During the second half of the study period, TPC was primarily performed for 52 pneumothoraces. All the thoracoscopic surgeries were successfully performed without serious complications (≥ Clavien-Dindo grade III). The median follow-up periods after LPC/TPC were 66/34 months, respectively. Pneumothorax recurrence rates after LPC at 2.5/5/7.5 years postoperatively were 5.4/12/42%, respectively; none of the patients who had underwent TPC developed postoperative pneumothorax recurrence (P = 0.032).

Conclusions

TPC might be an effective option for surgical treatment of intractable pneumothorax in patients with BHDS.

Electronic supplementary material

The online version of this article (10.1186/s13023-018-0790-x) contains supplementary material, which is available to authorized users.

Birt-Hogg-Dubé Syndrome: A Review of Dermatological Manifestations and Other Symptoms

Birt-Hogg-Dubé syndrome (BHD) is an autosomal dominant genodermatosis with malignant potential characterized by cutaneous and extracutaneous stigmata. Aberrations in the folliculin (FLCN) gene, which is located on chromosome 17, have been discovered in individuals with this condition. Over 150 unique mutations have been identified in BHD. The skin lesions associated with this condition include fibrofolliculomas, trichodiscomas, perifollicular fibromas, and acrochordons. Extracutaneous features of the syndrome typically include the lung (spontaneous pneumothorax and cysts) and the kidney (neoplasms). The only malignancies associated with BHD are renal cancers; however, other tumors have been observed in individuals with BHD. In this article, the skin lesions associated with this condition are reviewed, lung and renal manifestations associated with this syndrome are presented, and malignancies occurring in these patients are summarized.

Difference of the progression of pulmonary cysts assessed by computed tomography among COPD, lymphangioleiomyomatosis, and Birt-Hogg-Dubé syndrome

Many groups developed the methods to quantitatively analyze low attenuation area (LAA) on chest CT in patients with cystic lung diseases. Especially in COPD, it was reported that the cumulative size distribution of LAA clusters follows a power law characterized by the exponent D, which reflect the fractal dimension of terminal airspace geometry. We hypoyhesized that the quantitative charateristics of LAA clusters including fractal property might indicate the different features of the progression of cysts in cystic lung diseases. The aim of this study was to apply the CT image-based method of characterizing the size distribution of LAA clusters for lymphangioleiomyomatosis (LAM) and Birt-Hogg-Dubé syndrome (BHDS) to disclose their features of the progression of pulmonary cysts. 40 patients with COPD, 52 patients with LAM, and 18 patients with BHDS who had undergone CT scans at our institute between January 2002 and August 2009 were included. Differences among these diseases in the quantitative characteristics of LAA clusters {i.e., extent, number, size, fractal property, and the relationship between these quantitatives} were assessed. The Chi-sqsuare test, unpaired t-test, and one-way analyses of variance with Tukey post-hoc tests were used to compare groups, spline model with an interaction terms were used to assess the relationship between extent and number, and exponential regression model was used to assess the relationship between extent and size. Statistically significant differences separated the three diseases in extent and number (P < 0.001). Number was significantly correlated with extent in COPD (P < 0.001), but was not so in LAM and BHDS when extent exceeded 11.5% and 20.8%, respectively. Size was significantly correlated with extent in COPD and LAM (P < 0.001), but was not so in BHDS. The percentage of CT images with fractal property was higher in COPD than that in LAM and BHDS (95.8%, 92.9% and 63.0%, respectively). In conclusion, our study has demonstrated for the first time the different characteristics of the size distribution of LAA clusters among COPD, LAM and BHDS, and indicated that this method is useful for exploration of the pathophysiology in cystic lung diseases.

Novel clinical scoring system to identify patients with pneumothorax with suspicion for Birt-Hogg-Dubé syndrome

BACKGROUND AND OBJECTIVE

Birt-Hogg-Dubé syndrome (BHDS) is a rare hereditary disease that presents with multiple lung cysts and pneumothorax (PTX). Although some reports propose that findings from chest computed tomography enable one to distinguish BHDS from primary spontaneous pneumothorax (PSP), it is still unclear whether clinical features are useful for identifying patients with suspicion of BHDS from those with PTX.

METHODS

We retrospectively reviewed the medical records of patients with PTX who underwent video-assisted thoracoscopic surgery at Nissan Tamagawa Hospital from January 2012 to December 2015.

RESULTS

We identified a total of 1141 patients with PTX, including 54 with BHDS and 517 with PSP. Among them, logistic regression analysis segregated five features that were significantly associated with BHDS: familial history of PTX, past history of bilateral PTX, age at the first episode of PTX (≥25 years old (y.o.)), body mass index (≥18.5) and gender (female). We assigned scores of 3, 3, 2, 2 and 1 to the five features, respectively, to establish a system with a calculated score from 0 to 11. The cut-off value of a calculated score ≥ 4 yielded the highest sensitivity of 93% and specificity of 86%. Receiver operating characteristic (ROC) analysis showed the area under the curve reflecting an accuracy of this diagnostic test as 0.953.

CONCLUSION

BHDS has several clinical features distinct from PSP. Our scoring system consists of only five clinical variables that are easily evaluated and efficiently separate BHDS patients from those who have PTX without relying on an imaging study. Further prospective study is needed to confirm our findings.

Parsimony or poor luck: Concurrent Birt-Hogg- Dubé Syndrome and sarcoidosis

While sarcoidosis is notorious for myriad manifestations including cystic lung changes, we present a case with both Birt-Hogg-Dubé syndrome (BHD) and pulmonary sarcoidosis. BHD is a rare, autosomal dominant genetic disorder characterized by numerous thin-walled, irregular cysts, but lung function is typically normal otherwise. We present a case with confirmed BHD syndrome and concurrent granulomatous lung disease consistent with sarcoidosis. (Sarcoidosis Vasc Diffuse Lung Dis 2017; 34: 194-196).

Diagnosis and treatment of cystic lung disease

Cystic lung disease (CLD) is a group of lung disorders characterized by the presence of multiple cysts, defined as air-filled lucencies or low-attenuating areas, bordered by a thin wall (usually < 2 mm). The recognition of CLDs has increased with the widespread use of computed tomography. This article addresses the mechanisms of cyst formation and the diagnostic approaches to CLDs. A number of assessment methods that can be used to confirm CLDs are discussed, including high-resolution computed tomography, pathologic approaches, and genetic/ serologic markers, together with treatment modalities, including new therapeutic drugs currently being evaluated. The CLDs covered by this review are lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, Birt-Hogg-Dube syndrome, lymphocytic interstitial pneumonia/follicular bronchiolitis, and amyloidosis.

Birt-Hogg-Dubé syndrome: a case report and a review of the literature

Background: Birt-Hogg-Dubé syndrome (BHDS) is a rare autosomal dominant inherited syndrome caused by mutations in the folliculin coding gene (FLCN). The clinical manifestations of the syndrome involve the skin, lungs, and kidneys. Because of the rarity of the syndrome, guidelines for diagnosis and management of the patients with BHDS are lacking.

Objective: To present a case story and a review of the literature on BHDS in order to give an update on genetics, clinical manifestations, diagnosis, treatment, prognosis and follow-up strategies.

Design: Literature review and case story.

Results: A PubMed and Embase search identified 330 papers. BHDS is characterized by small benign tumors in the skin, spontaneous pneumothoraces caused by cysts in the lungs and a seven-fold increased risk of renal cancer. A case story of a young female patient presenting with pneumothorax and a family history of recurrent pneumothoraces in many relatives illustrates how the history and the diagnostic work up resulted in a diagnosis of BHDS.

Conclusion: BHDS is a rare inherited disorder. In patients with spontaneous pneumothorax or cystic lung disease without any obvious explanation, BHDS should be considered. Concomitant skin manifestations, a family history of familiar pneumothorax, renal cancers and skin manifestations supports the suspicion of BHDS. Early diagnosis is important in order to subject patients to systematic screening for renal cancers. A radiological surveillance strategy for renal cancer is proposed.

Haploinsufficiency of the folliculin gene leads to impaired functions of lung fibroblasts in patients with Birt-Hogg-Dubé syndrome

Birt–Hogg–Dubé syndrome (BHDS) is an autosomal dominant inherited disorder caused by germline mutations in the FLCN gene, and characterized by skin fibrofolliculomas, multiple lung cysts, spontaneous pneumothorax, and renal neoplasms. Pulmonary manifestations frequently develop earlier than other organ involvements, prompting a diagnosis of BHDS. However, the mechanism of lung cyst formation and pathogenesis of pneumothorax have not yet been clarified. Fibroblasts were isolated from lung tissues obtained from patients with BHDS (n = 12) and lung cancer (n = 10) as controls. The functional abilities of these lung fibroblasts were evaluated by the tests for chemotaxis to fibronectin and three‐dimensional (3‐D) gel contraction. Fibroblasts from BHDS patients showed diminished chemotaxis as compared with fibroblasts from controls. Expression of fibronectin and TGF‐β1 was significantly reduced in BHDS fibroblasts when assessed by qPCR. Addition of TGF‐β1 in culture medium of BHDS lung fibroblasts significantly restored these cells' abilities of chemotaxis and gel contraction. Human fetal lung fibroblasts (HFL‐1) exhibited reduced chemotaxis and 3‐D gel contraction when FLCN expression was knocked down. To the contrary, a significant increase in chemotactic activity toward to fibronectin was demonstrated when wild‐type FLCN was overexpressed, whereas transduction of mutant FLCN showed no effect on chemotaxis. Our results suggest that FLCN is associated with chemotaxis in lung fibroblasts. Together with reduced TGF‐β1 expression by BHDS lung fibroblasts, a state of FLCN haploinsufficiency may cause lung fibroblast dysfunction, thereby impairing tissue repair. These may reveal one mechanism of lung cyst formation and pneumothorax in BHDS patients.

Risk of spontaneous pneumothorax due to air travel and diving in patients with Birt-Hogg-Dubé syndrome

Background and objectives

Birt–Hogg–Dubé syndrome is an autosomal dominant disorder characterized by skin fibrofolliculomas, lung cysts, spontaneous pneumothorax and renal cell cancer due to germline folliculin (FLCN) mutations (Menko et al. in Lancet Oncol 10(12):1199–1206, 2009). The aim of this study was to evaluate the incidence of spontaneous pneumothorax in patients with BHD during or shortly after air travel and diving.

Methods

A questionnaire was sent to a cohort of 190 BHD patients and the medical files of these patients were evaluated. The diagnosis of BHD was confirmed by FLCN mutations analysis in all patients. We assessed how many spontaneous pneumothoraces (SP) occurred within 1 month after air travel or diving.

Results

In total 158 (83.2 %) patients returned the completed questionnaire. A total of 145 patients had a history of air travel. Sixty-one of them had a history of SP (42.1 %), with a mean of 2.48 episodes (range 1–10). Twenty-four (35.8 %) patients had a history of pneumothorax on both sides. Thirteen patients developed SP < 1 month after air travel (9.0 %) and two patients developed a SP < 1 month after diving (3.7 %). We found in this population of BHD patients a pneumothorax risk of 0.63 % per flight and a risk of 0.33 % per episode of diving. Symptoms possible related to SP were perceived in 30 patients (20.7 %) after air travel, respectively in ten patients (18.5 %) after diving.

Conclusion

Based on the results presented in this retrospective study, exposure of BHD patients to considerable changes in atmospheric pressure associated with flying and diving may be related to an increased risk for developing a symptomatic pneumothorax. Symptoms reported during or shortly after flying and diving might be related to the early phase of pneumothorax. An individualized advice should be given, taking also into account patients’ preferences and needs.

Genetic, epidemiologic and clinicopathologic studies of Japanese Asian patients with Birt-Hogg-Dubé syndrome

Birt-Hogg-Dubé syndrome (BHD) is a rare genetic disorder characterized by fibrofolliculomas, pulmonary cysts and renal cell carcinomas (RCCs). The affected individuals inherit germline mutations in the folliculin gene (FLCN). We investigated the mutation spectrum and clinicopathologic findings of 312 patients from 120 different families (119 Japanese and 1 Taiwanese). A total of 31 different FLCN sequence variants were identified. The majority were c.1285dupC (n = 34), c.1533_1536delGATG (n = 25), and c.1347_1353dupCCACCCT (n = 19). Almost all patients presented with pulmonary cysts. The incidence of RCCs in FLCN mutation carriers over the age of 40 was 34.8% (40/115). Fifty-five RCC lesions were surgically resected; most were either chromophobe RCC (n = 24; 43.6%) or hybrid oncocytic/chromophobe tumors (19; 34.5%). Seventy-six of 156 FLCN mutation carriers (120 probands and 36 sibs, 48.7%) had skin papules; however, cutaneous manifestations were so subtle that only one patient voluntarily consulted dermatologists. Japanese Asian BHD families have three FLCN mutational hotspots. Recurrent episodes of pneumothoraces are the major symptoms suggestive of a BHD diagnosis in our cohort. Characteristic features of lung and kidney lesions may be more informative than fibrofolliculomas as diagnostic criteria for BHD in the Japanese Asian population.

Pulmonary Neoplasms in Patients with Birt-Hogg-Dubé Syndrome: Histopathological Features and Genetic and Somatic Events

Birt-Hogg-Dubé syndrome (BHD) is an inherited disorder caused by genetic mutations in the folliculin (FLCN) gene. Individuals with BHD have multiple pulmonary cysts and are at a high risk for developing renal cell carcinomas (RCCs). Currently, little information is available about whether pulmonary cysts are absolutely benign or if the lungs are at an increased risk for developing neoplasms. Herein, we describe 14 pulmonary neoplastic lesions in 7 patients with BHD. All patients were confirmed to have germline FLCN mutations. Neoplasm histologies included adenocarcinoma in situ (n = 2), minimally invasive adenocarcinoma (n = 1), papillary adenocarcinoma (n = 1), micropapillary adenocarcinoma (n = 1), atypical adenomatous hyperplasia (n = 8), and micronodular pneumocyte hyperplasia (MPH)-like lesion (n = 1). Five of the six adenocarcinoma/MPH-like lesions (83.3%) demonstrated a loss of heterozygosity (LOH) of FLCN. All of these lesions lacked mutant alleles and preserved wild-type alleles. Three invasive adenocarcinomas possessed additional somatic events: 2 had a somatic mutation in the epidermal growth factor receptor gene (EGFR) and another had a somatic mutation in KRAS. Immunohistochemical analysis revealed that most of the lesions were immunostained for phospho-mammalian target of rapamycin (p-mTOR) and phospho-S6. Collective data indicated that pulmonary neoplasms of peripheral adenocarcinomatous lineage in BHD patients frequently exhibit LOH of FLCN with mTOR pathway signaling. Additional driver gene mutations were detected only in invasive cases, suggesting that FLCN LOH may be an underlying abnormality that cooperates with major driver gene mutations in the progression of pulmonary adenocarcinomas in BHD patients.

Mechanisms of pulmonary cyst pathogenesis in Birt-Hogg-Dube syndrome: The stretch hypothesis

Loss-of-function mutations in the folliculin gene (FLCN) on chromosome 17p cause Birt-Hogg-Dube syndrome (BHD), which is associated with cystic lung disease. The risk of lung collapse (pneumothorax) in BHD patients is 50-fold higher than in the general population. The cystic lung disease in BHD is distinctive because the cysts tend to be basilar, subpleural and lentiform, differentiating BHD from most other cystic lung diseases. Recently, major advances in elucidating the primary functions of the folliculin protein have been made, including roles in mTOR and AMPK signaling via the interaction of FLCN with FNIP1/2, and cell-cell adhesion via the physical interaction of FLCN with plakophilin 4 (PKP4), an armadillo-repeat containing protein that interacts with E-cadherin and is a component of the adherens junctions. In addition, in just the last three years, the pulmonary impact of FLCN deficiency has been examined for the first time. In mouse models, evidence has emerged that AMPK signaling and cell-cell adhesion are involved in alveolar enlargement. In addition, the pathologic features of human BHD cysts have been recently comprehensively characterized. The "stretch hypothesis" proposes that cysts in BHD arise because of fundamental defects in cell-cell adhesion, leading to repeated respiration-induced physical stretch-induced stress and, over time, expansion of alveolar spaces particularly in regions of the lung with larger changes in alveolar volume and at weaker "anchor points" to the pleura. This hypothesis ties together many of the new data from cellular and mouse models of BHD and from the human pathologic studies. Critical questions remain. These include whether the consequences of stretch-induced cyst formation arise through a destructive/inflammatory program or a proliferative program (or both), whether cyst initiation involves a "second hit" genetic event inactivating the remaining wild-type copy of FLCN (as is known to occur in BHD-associated renal cell carcinomas), and whether cyst initiation involves exclusively the epithelial compartment versus an interaction between the epithelium and mesenchyme. Ultimately, understanding the mechanisms of cystic lung disease in BHD may help to elucidate the pathogenesis of primary spontaneous pneumothorax, with more than 20,000 cases reported annually in the United States alone.

Birt-Hogg-Dubé syndrome: Clinical and molecular aspects of recently identified kidney cancer syndrome

Birt-Hogg-Dubé syndrome is an autosomal dominantly inherited disease that predisposes patients to develop fibrofolliculoma, lung cysts and bilateral multifocal renal tumors, histologically hybrid oncocytic/chromophobe tumors, chromophobe renal cell carcinoma, oncocytoma, papillary renal cell carcinoma and clear cell renal cell carcinoma. The predominant forms of Birt-Hogg-Dubé syndrome-associated renal tumors, hybrid oncocytic/chromophobe tumors and chromophobe renal cell carcinoma are typically less aggressive, and a therapeutic principle for these tumors is a surgical removal with nephron-sparing. The timing of surgery is the most critical element for postoperative renal function, which is one of the important prognostic factors for Birt-Hogg-Dubé syndrome patients. The folliculin gene (FLCN) that is responsible for Birt-Hogg-Dubé syndrome was isolated as a novel tumor suppressor for kidney cancer. Recent studies using murine models for FLCN, a protein encoded by the FLCN gene, and its two binding partners, folliculin-interacting protein 1 (FNIP1) and folliculin-interacting protein 2 (FNIP2), have uncovered important roles for FLCN, FNIP1 and FNIP2 in cell metabolism, which include AMP-activated protein kinase-mediated energy sensing, Ppargc1a-driven mitochondrial oxidative phosphorylation and mTORC1-dependent cell proliferation. Birt-Hogg-Dubé syndrome is a hereditary hamartoma syndrome, which is triggered by metabolic alterations under a functional loss of FLCN/FNIP1/FNIP2 complex, a critical regulator of kidney cell proliferation rate; a mechanistic insight into the FLCN/FNIP1/FNIP2 pathway could provide us a basis for developing new therapeutics for kidney cancer.

Diffuse Cystic Lung Disease. Part II

The diffuse cystic lung diseases have a broad differential diagnosis. A wide variety of pathophysiological processes spanning the spectrum from airway obstruction to lung remodeling can lead to multifocal cyst development in the lung. Although lymphangioleiomyomatosis and pulmonary Langerhans cell histiocytosis are perhaps more frequently seen in the clinic, disorders such as Birt-Hogg-Dubé syndrome, lymphocytic interstitial pneumonia, follicular bronchiolitis, and light-chain deposition disease are increasingly being recognized. Obtaining an accurate diagnosis can be challenging, and management approaches are highly disease dependent. Unique imaging features, genetic tests, serum studies, and clinical features provide invaluable clues that help clinicians distinguish among the various etiologies, but biopsy is often required for definitive diagnosis. In part II of this review, we present an overview of the diffuse cystic lung diseases caused by lymphoproliferative disorders, genetic mutations, or aberrant lung development and provide an approach to aid in their diagnosis and management.

Pleural Covering Application for Recurrent Pneumothorax in a Patient with Birt-Hogg-Dubé Syndrome

Birt-Hogg-Dubé syndrome (BHDS) is a rare hereditary disease that presents with multiple lung cysts and recurrent pneumothorax. These cysts occupy predominantly the lower-medial zone of the lung field adjacent to the interlobar fissure, and some of them abut peripheral pulmonary vessels. For the surgical management of pneumothorax with BHDS, the conventional approach of resecting all subpleural cysts and bullae is not feasible. Thus, after handling several bullae by using a stapler or performing ligation as a standardized treatment, we applied to a pleural covering technique to thicken the affected visceral pleura and then to prevent recurrence of pneumothorax. We herein report the successful application of a pleural covering technique via thoracoscopic surgery to treat the recurrent pneumothorax of a 30-year-old man with BHDS. This technique is promising for the management of intractable pneumothorax secondary to BHDS.

Partial pleural covering for intractable pneumothorax in patients with Birt-Hogg-Dubé Syndrome

BACKGROUND AND AIMS

Birt-Hogg-Dubé syndrome (BHD) is an inherited disorder associated with a germline mutation of the folliculin (FLCN) gene. Most patients with BHD have multiple pulmonary cysts, and are at high risk of repeated pneumothorax. Although an increasing number of patients are diagnosed with BHD by genetic testing, therapeutic approaches for intractable pneumothorax have not yet been described.

METHODS

We treated three patients who had repeated episodes of pneumothorax. All had multiple pulmonary cysts in the lower lobes, and two had a family history of pneumothorax. Video-assisted thoracic surgery was used to perform wedge resections and partial pleural covering of the cystic lesions. The partial pleural covering technique used sheets of polyglycolic acid felt or regenerative oxidized cellulose mesh. The resected tissues underwent histopathological evaluation, and peripheral blood leukocytes were tested for FLCN mutations.

RESULTS

The operative times were less than 2 h, and there were no complications. The resected cysts had histopathological features characteristic of BHD lung. All patients were found to have FLCN germline mutations; thus their repeated pneumothoraces were a manifestation of BHD. None of the patients developed respiratory problems after undergoing the partial pleural covering procedure, and they have all been well without pneumothorax for 30 months or more.

CONCLUSIONS

Partial pleural covering combined with resection of protruding cysts should be a safe and effective therapeutic approach for BHD patients with intractable pneumothorax. Further investigation is needed to establish a detailed protocol for treatment of pneumothorax that results in minimal functional impairment.

Folliculin regulates cell-cell adhesion, AMPK, and mTORC1 in a cell-type-specific manner in lung-derived cells

Germline loss‐of‐function BHD mutations cause cystic lung disease and hereditary pneumothorax, yet little is known about the impact of BHD mutations in the lung. Folliculin (FLCN), the product of the Birt–Hogg–Dube (BHD) gene, has been linked to altered cell–cell adhesion and to the AMPK and mTORC1 signaling pathways. We found that downregulation of FLCN in human bronchial epithelial (HBE) cells decreased the phosphorylation of ACC, a marker of AMPK activation, while downregulation of FLCN in small airway epithelial (SAEC) cells increased the activity of phospho‐S6, a marker of mTORC1 activation, highlighting the cell type–dependent functions of FLCN. Cell–cell adhesion forces were significantly increased in FLCN‐deficient HBE cells, consistent with prior findings in FLCN‐deficient human kidney‐derived cells. To determine how these altered cell–cell adhesion forces impact the lung, we exposed mice with heterozygous inactivation of Bhd (similarly to humans with germline inactivation of one BHD allele) to mechanical ventilation at high tidal volumes. Bhd^+/− mice exhibited a trend (P = 0.08) toward increased elastance after 6 h of ventilation at 24 cc/kg. Our results indicate that FLCN regulates the AMPK and mTORC1 pathways and cell–cell adhesion in a cell type–dependent manner. FLCN deficiency may impact the physiologic response to inflation‐induced mechanical stress, but further investigation is required. We hypothesize that FLCN‐dependent effects on signaling and cellular adhesion contribute to the pathogenesis of cystic lung disease in BHD patients.

We found that downregulation of FLCN in human bronchial epithelial (HBE) cells decreased the phosphorylation of ACC, a marker of AMPK activation, while downregulation of FLCN in small airway epithelial (SAEC) cells increased the activity of phospho‐S6, a marker of mTORC1 activation, highlighting the cell type–dependent functions of FLCN. Cell–cell adhesion forces were significantly increased in FLCN‐deficient HBE cells, consistent with prior findings in FLCN‐deficient human kidney‐derived cells. To determine how these altered cell–cell adhesion forces impact the lung, we exposed mice with heterozygous inactivation of Bhd (similarly to humans with germline inactivation of one BHD allele) to mechanical ventilation at high tidal volumes. Bhd+/− mice exhibited a trend (P = 0.08) toward increased elastance after 6 h of ventilation at 24 cc/kg.

Spontaneous pneumothorax as indicator for Birt-Hogg-Dubé syndrome in paediatric patients

Background

Birt-Hogg-Dubé syndrome (BHD) is a rare autosomal dominantly inherited disorder caused by germline mutations in the folliculin (FLCN) gene. Clinical manifestations of BHD include skin fibrofolliculomas, renal cell cancer, lung cysts and (recurrent) spontaneous pneumothorax (SP). All clinical manifestations usually present in adults > 20 years of age.

Case presentations

Two non-related patients with (recurrent) pneumothorax starting at age 14 accompanied by multiple basal lung cysts on thoracic CT underwent FLCN germline mutation analysis. A pathogenic FLCN mutation was found in both patients confirming suspected BHD. The family history was negative for spontaneous pneumothorax in both families.

Conclusion

Although childhood occurrence of SP in BHD is rare, these two cases illustrate that BHD should be considered as cause of SP in children.