Differentiation between Birt-Hogg-Dubé syndrome and lymphangioleiomyomatosis: quantitative analysis of pulmonary cysts on computed tomography of the chest in 66 females

Backgrounds: Since Birt-Hogg-Dubé syndrome (BHDS) and lymphangioleiomyomatosis (LAM) share some clinical manifestations (multiple pulmonary cysts with pneumothorax, renal tumors, and sometimes skin lesions), the differential diagnosis of the two diseases becomes problem especially in female patients. This study aims to quantify pulmonary cysts in computed tomography (CT) of females with BHDS and those with LAM and also to identify the independent parameters for differentiating the two diseases.

Methods: Fourteen patients with BHDS and 52 with LAM were studied. In CT scans, lung fields were defined as areas with fewer than -200 Hounsfield units (HU) and pulmonary cysts as areas consisting of 10 or more consecutive pixels with fewer than -960 HU. The extent, number, size and circularity of cysts were calculated by using hand-made software and compared between the two diseases. Moreover, the lung fields were divided into six zones and analyzed for the distribution of cysts. Finally, a stepwise discriminant analysis employing quantitative measurements of cysts and clinical features was performed.

Results: The two diseases were significantly different in all quantitative measurements of cysts. Stepwise discriminant analysis accepted the following four variables: the family history of pneumothorax within the second degree relatives, lower-medial zone predominance of cysts, diffusing capacity and mean size of cysts in this order.

Conclusion: The quantitative characteristics of pulmonary cysts are significantly different between BHDS and LAM. The independent parameters for differentiating the two diseases are the family history of pneumothorax, zonal predominance of cysts, diffusing capacity and size of cysts.