Restated, an inflammatory disorder primarily localized in the subcutaneous fat is termed a "panniculitis," a group of disorders that may be challenging both for the clinician and the dermatopathologist.:487
It can occur in any fatty tissue (cutaneous or visceral) and is often diagnosed on the basis of a deep skin biopsy, and can be further classified by histological characteristics based on the location of the inflammatory cells (within fatty lobules or in the septa which separate them) and on the presence or absence of vasculitis.
There are thus four main histological subtypes:
Erythema induratum, or "Bazin disease", is a panniculitis on the back of the calves. It was formerly thought to be a reaction to the tuberculum bacillus. It is now considered a panniculitis that is not associated with a single defined pathogen.
Nodular vasculitis is a skin condition characterized by small, tender, reddened nodules on the legs, mostly on the calves and shins. Microscopically there are epithelioid granulomas and vasculitis in the subcutaneous tissue, making it a form of panicullitis. Most of these cases are now thought to be manifestation of tuberculosis and indeed they respond well to anti-tuberculous treatment.
Non-vasculitis forms of panniculitis that may occur include:
Traumatic panniculitis is a panniculitis that occurs following trauma to the skin.:492
Cold panniculitis is a panniculitis occurring after exposure to cold, most often seen in infants and young children.:491 This condition has been described in children who suck ice or popsicles, and therefore is sometimes referred to as "popsicle panniculitis.":491 The term was coined when a patient with a rash of unknown origin on her cheek was brought to a dermatologist.
Gouty panniculitis is a panniculitis caused by deposition of uric acid crystals in gout.:494
Pancreatic panniculitis (also known as "Enzymatic panniculitis," "Pancreatic fat necrosis," and "Subcutaneous fat necrosis") is a panniculitis most commonly associated with pancreatic carcinoma, and more rarely with anatomic pancreatic abnormalities, pseudocysts, or drug-induced pancreatitis.:493
Factitial panniculitis is a panniculitis that may be induced by the injection of organic materials, povidone, feces, saliva, vaginal fluid, and oils.:492
Panniculitis can also be classified based on the presence or absence of systemic symptoms. Panniculitis without systemic disease can be a result of trauma or cold; Panniculitis with systemic disease can be caused:
^Cotran, Ramzi S.; Kumar, Vinay; Fausto, Nelson; Nelso Fausto; Robbins, Stanley L.; Abbas, Abul K. (2005). Robbins and Cotran pathologic basis of disease (7th ed.). St. Louis, Mo: Elsevier Saunders. p. 1265. ISBN0-7216-0187-1.
^Winkelmann RK, Bowie EJ. Hemorrhagic diathesis associated with benign histiocytic cytophagic panniculitis and systemic histiocytosis. Arch Intern Med.1980; 140: 1460-3
^Smith K J, Skeleton H J, Yeagre J, Angritt P, Wagner K, James W. D., Giblin W. J., Lupton G. P. Cutaneous histopathological, immunohistochemical, and clinical manifestations inpatients with hemophagocytic syndrome. Military Medical Consortium for Applied Retroviral Research (MMCARR). Arch Dermatol 1992; 128: 193-200
^ abcRapini, Ronald P.; Bolognia, Jean L.; Jorizzo, Joseph L. (2007). Dermatology: 2-Volume Set. St. Louis: Mosby. p. 1515. ISBN1-4160-2999-0.