BACKGROUND: Birt-Hogg-Dubé (BHD) syndrome is a genetic condition caused by pathogenic variants in the FLCN gene resulting in benign skin lesions, spontaneous pneumothorax, and increased risk for a variety of renal tumors. Skin manifestations of BHD include trichodiscoma (TD) and fibrofolliculoma (FF), which may represent the same pathologic entity. These lesions can identify BHD patients, who upon positive genetic testing can be considered for life-long surveillance for renal neoplasms.
OBJECTIVE: To characterize patients diagnosed with TD and FF including rates and outcomes of genetics referral.
METHODS: Retrospective chart reviews of patients with confirmed or possible diagnosis of TD or FF at the University of Michigan from September 2002 through October 2020 to assess pathologic findings, personal and family history of BHD manifestations, referral for genetic evaluation, and genetic testing results.
RESULTS: 64 patients had a pathologic diagnosis of TD or FF, 16 of whom (25%) were referred to cancer genetics. Fourteen patients completed genetic evaluation, 9 of whom were diagnosed with BHD (64%), with 6 unique pathogenic variants in FLCN.
CONCLUSIONS: Providers should consider referral for genetic evaluation for patients with biopsy-proven TD or FF, as early diagnosis of BHD provides the opportunity for early detection and treatment of other BHD-associated conditions.

The diagnosis of patients with Birt-Hogg-Dubé (BHD) syndrome is always delayed (even for more than 10 years). Improving the understanding and diagnosis of this disease is vital for clinicians and radiologists. In this study we presented the chest computed tomography (CT) findings of BHD syndrome and offered suggestions for BHD cases with spontaneous pneumothorax.
Twenty-six BHD patients from 11 families (10 men, 16 women; mean age: 46 ± 12 years, 20-68 years) were included. The clinical features of the patients included pneumothorax, renal lesions, and skin lesions. Twenty-three patients underwent chest CT imaging. The cyst condition of each patient derived from reconstructed chest CT imaging was recorded, including the cyst number, size, volume, pattern, and distribution.
Pneumothorax occurred in 54% (14/26) of patients. Among them, 43% (6/14) had pneumothorax more than twice. However, typical skin and renal lesions were absent. Four patients had renal hamartoma. CT showed that 23 (100%) patients had lung cysts. Pulmonary cysts were bilateral and multiple, round, irregular, or willow-like. And 93.6% of the large cysts (long-axis diameter ≥ 20 mm) were under the pleura, and near the mediastinum and spine. The long-axis diameter, short-axis diameter and volume of the largest cysts were associated with the occurrence of pneumothorax (all P < 0.05).
Chest CT imaging can reveal some characteristic features of BHD syndrome. The occurrence of pneumothorax in BHD patients is closely related to their pulmonary cystic lesions.

Cutaneous adnexal tumors (CAT) are rare tumors originating from the adnexal epithelial parts of the skin. Due to its clinical and histopathological characteristics comparable with other diseases, clinicians and pathologists experience difficulties in its diagnosis.We aimed to reveal the clinical and histopathological characteristics of the retrospectively screened cases and to compare the prediagnoses and histopathological diagnoses of clinicians.
The data of the last 5 years were scanned and patients with histopathological diagnosis of CAT were included in the study.
A total of 65 patients, including 39 female and 26 male patients aged between 8 and 88, were included in the study. The female to male ratio was 1.5, and the mean age of the patients was 46.15 ± 21.8 years. The benign tumor rate was 95.4%, whereas the malignant tumor rate was 4.6%. 38.5% of the tumors were presenting sebaceous, 35.4% of them were presenting follicular, and 18.5% of them were presenting eccrine differentiation. It was most commonly seen in the head-neck region with a rate of 66.1%. When clinical and histopathological prediagnoses were compared, prediagnoses and histopathological diagnoses were compatible in 45% of the cases. Most frequently, it was the basal cell carcinoma, epidermal cyst, and sebaceous hyperplasia identified in preliminary diagnoses.
Cutaneous adnexal tumors are very important, as they can accompany different syndromes and may be malignant. Due to difficulties in its clinical diagnosis, histopathological examination must be performed from suspicious lesions for definitive diagnosis.

Birt-Hogg-Dubé syndrome (BHD) is an autosomal dominantly inherited cancer predisposition syndrome associated with an increased risk of spontaneous pneumothorax (SP) and renal cell carcinoma in the adult population. Recent studies suggest that BHD accounts for up to 10% of all SP in adults and BHD in children with SP have been reported.
To explore to what extent BHD is the cause of childhood pneumothorax, we studied a Danish BHD cohort consisting of 109 cases from 22 families. Clinical data was gathered by review of medical records. A systematic literature search concerning childhood and adolescence pneumothorax in BHD was performed and identified publications reviewed.
In our cohort, three of 109 BHD cases experienced childhood pneumothorax, corresponding to a prevalence of 3%. Reviewing the literature, data regarding more than 800 BHD cases were covered. Only seven previously published cases of childhood pneumothorax in BHD were identified.
Our findings suggest that BHD is likely the cause of a larger subset of childhood pneumothoraces than hitherto recognized. Awareness of BHD as a cause of childhood pneumothorax needs to be raised to provide patients and relatives with the possibility of specialized management of SP and regular renal cancer surveillance.

Birt-Hogg-Dubé syndrome (BHDS) is an autosomal dominantly inherited disorder characterized by multiple trichodiscomas, fibrofolliculomas, and acrocordons. There is also an increased risk of developing renal neoplasms and lung cysts/spontaneous pneumothorax. We present a 43-year-old man with multiple, 2~4 mm sized, dome-shaped, and skin-colored papules on his cheek and neck. On the basis of clinical finding and histopathologic examination on the cheek lesion, it was diagnosed as multiple trichodiscomas. Subsequently, molecular analysis revealed a mutation in the folliculin gene. We report a rare case of BHDS with a proved gene mutation.