Panniculitis: A summary

The diagnosis of panniculitis is felt to be a confusing topic by some pathologists. This summarical article presents inflammatory diseases of the subcutis in a systematic fashion, based on whether they are centered on fibrovascular septa or the adipose lobules, and whether morphologic vasculitis is present or not. Septocentric, non-vasculitis disorders include erythema nodosum, panniculitis that follows the use of "biological" therapeutic agents, lipodermatosclerosis, post-irradiation panniculitis, morphea profunda, and necrobiosis lipodica profunda. Polyarteritis nodosa and Behçet's disease are the conditions that are based in the subcutaneous septa with vasculitis. Predominantly-lobular panniculitides with no vasculitis include pancreatogenic panniculitis, the panniculitis of alpha-1-antitrypsin deficiency, panniculitis associated with lupus erythematosus and dermatomyositis, subcutaneous Sweet syndrome, eosinophilic panniculitis, factitial panniculitis, cold panniculitis, panniculitis following injections of corticosteroids, lipomembranous (ischemic) panniculitis; sclerema neonatorum and subcutaneous fat necrosis of the newborn, and Rosai-Dorfman disease of the subcutis. Erythema induratum and infectious panniculitis are vasculitic and lobulocentric conditions. This article reviews the histological features of these diseases.