A chest film should be performed if there are pulmonary symptoms, as lung involvement may occur and is quite responsive to systemic corticosteroids. Age-appropriate cancer screening and evaluation for inflammatory bowel disease are indicated if no other underlying cause is found, especially in patients with bullous or ulcerative lesions. Skin biopsy should be performed to confirm the diagnosis. The classic histopathologic pattern consists of a dense diffuse neutrophilic infiltrate in the reticular dermis. Leukocytoclastic nuclear debris is typically present interstitially, and there is commonly massive papillary dermal edema.
Eosinophils are present in some instances, but neutrophils usually predominate.
The epidermis is usually spared, although nonspecific findings such as spongiosis and subcorneal pustule formation can be seen. Direct immunofluorescence testing is non-contributory. Rarely, the inflammation extends to involve the subcutis. In essentially all instances, those cases with subcutaneous involvement will also show extensive involvement of the reticular dermis. Pulmonary infiltrates also tend to respond promptly to prednisone.