BHD causes pneumothoraces during childhood in rare cases

Birt-Hogg-Dubé Syndrome is caused by inactivating mutations in the FLCN gene, characterised by skin lesions on the face and upper body; lung cysts and predisposition to pneumothorax; and kidney cancer. Although symptoms typically appear in the third and fourth decade of life, Johannesma et al. (2014) suggest that pneumothorax in patients under the age of 18 might be underdiagnosed.

In two large cohort studies, 24% were found to have had one or more episodes of pneumothorax, with a predicted lifetime risk of29% of developing a pneumothorax (Houweling et al., 2011, Toro et al., 2007). The age range of patients’ initial pneumothorax episodes was 18 – 74 years, with a median age of 36 – 38 years, suggesting that the age of onset of this symptom can vary widely (Houweling et al., 2011, Toro et al., 2007). However, the majority of families in both of these studies were recruited via dermatology clinics, meaning that there might be some ascertainment bias in these cohorts.

Johannesma et al. report the cases of two unrelated Dutch BHD patients who suffered their first pneumothorax at the age of 14. Both patients were given chest CT scans, as they suffered recurrent episodes as teenagers, and revealed the presence of lung cysts in the lower lobes of the lungs. Genetic testing confirmed each had a pathogenic FLCN mutation, confirming a diagnosis of BHD.

This report follows three other reports of BHD patients suffering pneumothoraces as teenagers: a 7 year old French boy (Bessis et al., 2006); a 16 year old Japanese girl (Gunji et al., 2007); and an 18 year old Dutch girl (Houweling et al., 2011). Thus, although pneumothorax during childhood is rare in BHD patients, both clinicians and BHD patients with children should be aware that it is a possibility.

It is possible that BHD is underdiagnosed in cases of paediatric spontaneous pneumothorax as BHD is normally considered to be an adult-onset disease. Additionally, CT scans – which would help diagnose BHD if lung cysts were found – are not normally administered to paediatric patients, unless deemed to be absolutely necessary, due to the low dose of radiation patients are exposed to during the scan (Balfour-Lynn et al., 2005).

Given that both patients reported by Johannesma et al. were found to have lung cysts as teenagers but neither had yet developed skin or kidney symptoms, it is possible that lung cysts are the first symptom of BHD to develop, but are not normally found unless the patient receives a chest CT for some other reason. Indeed, pneumothorax risk is strongly correlated with increased number and size of lung cysts (Toro et al., 2007), and it has subsequently been hypothesised that lung collapses are caused by air-filled cysts rupturing and releasing air into the chest cavity (Furuya and Nakatani, 2013). Thus it is likely that all the reported paediatric patients also developed lung cysts in childhood.

Four of the five paediatric BHD patients did have recurrent episodes, with one patient having four recurrent lung collapses before the age of 18 (Johannesma et al. 2014), and another having six episodes between the ages of 16 and 38 (Gunji et al., 2007). Given that the average number of pneumothoraces per patient was found to be two in the cohort studied by Toro et al. this does suggest that BHD patients who have their first pneumothorax in childhood might be at higher risk of recurrent episodes than other BHD patients.

Thus, although BHD patients suffer pneumothoraces during childhood only in rare cases, as childhood pneumothorax is itself rare, only affecting 4 in 100,000 boys and 1 in 100,000 girls, Johannesma et al. recommend that a thorough family history, a low dose CT scan, and genetic testing should be considered for paediatric patients who experience repeated episodes of spontaneous pneumothorax.

 

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 www.bhdsyndrome.org – the primary online resource for anyone interested in BHD Syndrome.

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