Panniculitis

Panniculitis is a group of diseases whose hallmark is inflammation of subcutaneous adipose tissue (the fatty layer under the skin – panniculus adiposus). Symptoms include tender skin nodules, and systemic signs such as weight loss and fatigue.
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. The general term for inflammation of any adipose tissue is steatitis.
Signs and symptoms.
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 by:
This is not a complete list of possible causes.
Associated conditions.
Lipoatrophy or lipodystrophy (the loss of subcutaneous adipose tissue) can occur in any of these conditions.
Diagnosis.
Classification.
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:
Lobular.
With vasculitis.
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 panniculitis. Most of these cases are now thought to be manifestation of tuberculosis and indeed they respond well to anti-tuberculous treatment.
Without vasculitis.
Non-vasculitis forms of panniculitis that may occur include:
With needle-shaped clefts.
Lipodermatosclerosis is a form of panniculitis associated with chronic venous insufficiency that presents with brown indurations on the front of the shins. It may be associated with pain and other signs of chronic venous insufficiency. The exact cause is unknown.
Other forms include:
Septal.
Erythema nodosum.
Erythema nodosum is a form of panniculitis characterised by tender red nodules, 1–10 cm, associated with systemic symptoms including fever, malaise, and joint pain. Nodules may become bluish-purple, yellowing, and green, and subside over a period of 2–6 weeks without ulcerating or scarring. Erythema nodosum is associated with infections, including Hepatitis C, EBV and tuberculosis, Crohn's disease and sarcoidosis, pregnancy, medications including sulfonamides, and some cancers, including Non-Hodgkin lymphoma and pancreatic cancer.
A1AT-deficiency-associated.
Alpha-1 antitrypsin deficiency panniculitis is a panniculitis associated with a deficiency of the α1-antitrypsin enzyme.