This week’s blog post contains a round-up of the latest case reports for Birt-Hogg-Dubé Syndrome (BHD) in the literature.
Case Report 1
Firstly, a case report by Degheili et al., documents BHD in 2 individuals with kidney cysts but no kidney tumours. As opposed to tumours, which are solid masses of unusual tissue, cysts are small sacs normally filled with air or fluid. Kidney cysts do not normally impact the function of the kidney but in rare cases can grow large enough to cause pain or discomfort and can block the flow of urine through the kidneys.
The first case was a 70-year-old woman referred for investigation of cysts on her lungs. The patient also had innumerable pale skin bumps on her face and upper torso which were later confirmed to be fibrofolliculomas. A CT scan of her kidneys revealed bilateral cysts and were considered simple. The patient was followed for four years and both lung and kidney cysts remained stable, with the formation of no new cysts.
The second case was a 50-year-old woman with a personal and family history of recurrent pneumothoraces, as well as several skin lesions characteristic of BHD. Genetic testing of the folliculin gene confirmed the diagnosis of BHD. CT scans revealed cysts on both her lungs and kidneys with no kidney tumours.
It is questioned whether the presence of kidney cysts is an incidental finding, or a true feature of BHD. Renal cysts are found in as many as 4 in 10 people in the general population. However, these tend to be isolated, unilateral and simple, compared with the multiple bilateral cysts found in these patients, and in the reported literature on kidney cysts in BHD. However, without further documentation of kidney cysts on a larger scale, an association cannot yet be made.
Case Report 2
In this case report by Lakhani et al., BHD was diagnosed through incidental findings on a lung CT scan. A 59-year-old male presented to the hospital following a CT scan of the lung, abdomen and kidney as part of a trauma workup which revealed the presence of lung cysts. A second CT scan of the chest showed multiple, thin-walled, cysts with a basal distribution (i.e. cysts were located at the bottom of the lungs). The patient had no personal or family history of spontaneous pneumothoraces or kidney cancer. Despite this, and due to the characteristics of the cysts in the lung, BHD was suspected and was confirmed by genetic testing.
BHD is thought to remain underdiagnosed, partly due to variation in clinical presentation as well as lack of awareness. This case report highlights the importance of spreading awareness of BHD within the medical community, as lung cysts found incidentally on imaging studies may be the first sign of BHD in many cases. Early diagnosis of BHD can be critical in minimising the risk of kidney cancer. The BHD Foundation is creating a BHD awareness leaflet that will be circulated to the doctors who are likely to come across the first signs of BHD including dermatologists (skin doctors), radiologists (doctors who review images) and lung doctors
Case Report 3
The final case report documents a 37-year-old male who was admitted to hospital with lower back pain and hematuresis (blood in the urine). The patient had a personal and family history of spontaneous pneumothorax. A CT scan of the kidney showed a mass on the right kidney and robotic-assisted surgery was performed to remove the tumour. It was noted that the tumour had an unusual shape, and upon further investigation of a sample of the tumour tissue, the tumour was considered as an unclassified type of renal cell carcinoma (RCC). This is unusual for individuals with BHD who normally present with chromophobe, oncocytoma or a hybrid chromophobe/oncocytoma type of RCC.
Genetic testing was performed and a mutation in the folliculin gene was found. In BHD, mutation of a single copy of folliculin is sufficient to cause the skin and lung manifestations, but it is thought that a mutation in the second copy is required for the development of kidney cancer. In this report, it appears that they did not observe a mutation in the second copy of folliculin in the kidney tumour tissue, however it is unclear whether any other genes known to be drivers of cancer development were analysed for mutations. If there were no other mutations and only a single copy of folliculin was mutated this report would represent a rare finding of kidney cancer in and individual with BHD.
Case reports such as these are invaluable additions to the BHD scientific literature that can raise questions about uncommon manifestations or highlight different routes to diagnosis that can increase our knowledge and understanding of the condition. As well as this, they can also help to raise awareness of BHD among clinicians which is an important aspect of the work of the BHD Foundation.