The panniculitides are a group of heterogeneous inflammatory diseases involving the subcutaneous fat. Traditionally, the clinical and the histopathological study of the panniculitides have been considered one of the most difficult subjects in dermatology. The reasons for this relative unpopularity of the panniculitides are varied. First, the lesions show a disappointing clinical monotony. The most disparate processes involving the subcutaneous fat have the same clinical morphology presenting as erythematous nodules generally located on the lower limbs. Therefore, the clinical findings are often not helpful in the differential diagnosis among the different inflammatory conditions involving the subcutis. Second, there is issue relative to the depth of the lesions that adds difficulty to the histopathologic study of these disorders. Sometimes biopsy specimens sent to the dermatopathology laboratories with a clinical diagnosis of panniculitis contain no subcutaneous fat at all. Pathologists and dermatopathologists also share some responsibility for the fact that panniculitides are considered to be the “ugly duck” of dermatopathology. Too often, a dermatopathologic report of a panniculitis is signed out with the diagnosis of septal panniculitis or lobular panniculitis, or even worse, mixed panniculitis, so that the report communicates little or nothing to the clinician. Dermatopathologists must recognize that a diagnosis of septal or lobular panniculitis is just the first step in the diagnostic process. Following that initial classification, efforts should be made to look for the characteristic histopathologic findings that allow for a more specific final diagnosis in the language of clinical dermatology. Another difficulty for the specific diagnosis of panniculitides results from the evolutive nature of the lesions. Like other inflammatory diseases of the skin, panniculitides constitute dynamic processes in which both the composition and the distribution of the inflammatory infiltrate cells change within the course of a few days. Biopsies from panniculitis are often taken from late-stage lesions due to inadequate clinicopathologic correlation and they show nonspecific findings. Clinicians are often reluctant to perform deep excisional biopsies for diagnosis of panniculitic disorders, because they think that many times a specific diagnosis will not be rendered by the dermatopathologist and because of the poor healing and scarring of large biopsies on the lower legs of women.
I think that this is an overly pessimistic view of the histopathology of panniculitides and that with an appropriate biopsy a specific diagnosis can usually be made. The purpose of this monography is to present a clinico-pathologic overview of some panniculitides. Emphasis will be placed on the characteristic histopathologic features for specific diagnosis, and
will include short comments about the treatment for each entity. In my experience, with appropriate specimens, adequate clinico-pathologic correlation, and pertinent histopathologic study a specific diagnosis may be rendered in most cases of panniculitis.
Luis Requena, MD
The panniculitides are a group of heterogeneous inflammatory diseases involving the subcutaneous fat. Traditionally, the clinical and the histopathological study of the panniculitides have been considered one of the most difficult subjects in dermatology. The reasons for this relative unpopularity of the panniculitides are varied. First, the lesions show
a disappointing clinical monotony.
The panniculitides represent a group of heterogeneous inflammatory diseases that involve the subcutaneous fat. The specific diagnosis of these diseases requires histopathologic study because different panniculitides usually show the same clinical appearance, which consists of erythematous nodules on the lower extremities.
Superficial thrombophlebitis (STP) is a common disease usually characterized by an auto-resolving vasculitis of medium-sized veins of the upper subcutis or deep dermis that clinically manifests as a tender or painful palpable cord-like structure.
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