The role of skin biopsy in diagnosis of panniculitides.

Several factors hamper the clinical and histologic diagnosis of panniculitis. Clinically the patients tend to present with erythematous subcutaneous nodules with quite a monotonous appearance, without additional symptoms. Histopathologically, as the subcutaneous fat responds to a variety of insults in a limited number of forms, there are sometimes subtle pathologic differences among the conditions. Although the biopsy plays a critical role in the diagnostic process of a panniculitis, a series of prerequisites must be met in order to obtain as much information as possible from this procedure. If the biopsy is inadequate, i.e., does not include sufficient subcutaneous fat or the site of sampling site/biopsy timing is wrong, histopathologic assessment is limited and the correct diagnosis may be delayed and further sampling may be required. This article introduces the reader to the field of panniculitides under the histopathologic perspective through a brief description of the normal histology of subcutaneous fat. I also includes the definition of the types of fat necrosis, role of biopsy of panniculitis and its rules and pitfalls, up to a microscopic approach of a slide.