Panniculitis is a group of diseases whose hallmark is inflammation of subcutaneous adipose tissue (the fatty layer under the skin – panniculus adiposus).

[1] Symptoms include tender skin nodules, and systemic signs such as weight loss and fatigue.

[citation needed] 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.

[citation needed] There are thus four main histological subtypes:[4] Erythema induratum, or "Bazin disease", is a panniculitis on the back of the calves.

[7] Nodular vasculitis is a skin condition characterized by small, tender, reddened nodules on the legs, mostly on the calves and shins.