Friday, December 2, 2011

Birt-Hogg-Dubé Syndrome

Birt-Hogg-Dubé syndrome is a rare autosomal-dominant multiorgan disorder that affects the skin, kidneys, and lungs.

Skin lesions include the characteristic triad of fibrofolliculomas (hamartomas of the hair follicles, 2- to 4-mm, smooth, dome-shaped papules), trichodiscomas (tumors of the hair disk), and acrochordons (skin tags).

Renal involvement includes a predisposition to hybrid chromophobe oncocytomas, chromophobe carcinomas, clear cell carcinomas, oncocytomas, and papillary renal cell carcinomas.

Pulmonary involvement manifests as cystic lung disease and spontaneous pneumothorax. The cysts are variable in shape and size, but are discrete and thin-walled. Larger cysts are usually multiseptated. The cysts tend to be larger and more numerous in the lower lobes, a distribution that can help differentiate Birt-Hogg-Dubé syndrome from other causes of multiple cystic lung lesions such as Langerhans cell histiocytosis and lymphangioleiomyomatosis (see below).

Patients present with the characteristic skin lesions in the 3rd–4th decades of life. Spontaneous pneumothorax occurs in about 1/4 of patients, and renal cancer develops in 15%–30% of patients with skin lesions.

The images above reveal a solid left renal lesion that turned out to be an oncocytoma, as well as cystic lung disease. Note that the typical cysts described are usually larger and more irregular in shape (see the article by Agarwal et al for the full spectrum).

Differential Diagnosis

The main differential consideration in a patient with a solid renal tumor and cystic lung disease is tuberous sclerosis. Sclerotic bone lesions, renal angiomyolipoma, and brain lesions support the latter diagnosis. The pattern and appearance of the cystic lung disease (see below) is also helpful.

The presence of pulmonary cysts without a solid renal tumor widens the differential diagnosis to include other causes of cystic lung disease:
  • Langerhans cell histiocytosis: Upper lung–predominant distribution of irregularly shaped cysts and nodules.
  • Lymphangioleiomyomatosis: Cysts are typically round, more uniform in size, and diffuse in distribution. Cysts are not as large as those in Birt-Hogg-Dubé syndrome.
  • Lymphocytic interstitial pneumonia: Characterized by ground-glass opacities, often in combination with cystic lesions. Typically seen in in patients with Sjögren syndrome, human immunodeficiency virus infection, and variable immunodeficiency syndromes.
  • Pneumocystis jiroveci pneumonia: Typically seen in immunocompromised patients. Look for associated ground-glass opacities.


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