panniculitisin

Panniculitis is a term for conditions that involve inflammation of the subcutaneous fat. It presents with tender nodules or plaques under the skin, most commonly on the legs, but may appear elsewhere. The lesions may vary in color and size and are sometimes accompanied by fever or malaise, depending on the underlying cause.

Pathology is used to classify panniculitis as septal (involving the connective tissue septa between fat lobules) or lobular (primarily involving the fat lobules themselves), and as with or without accompanying vasculitis. This histologic pattern helps guide diagnosis and management. The most familiar forms include erythema nodosum, a septal panniculitis without vasculitis, and erythema induratum (nodular vasculitis), a lobular panniculitis with vasculitis occurring typically on the calves. Other forms include pancreatic panniculitis associated with pancreatic disease, cold panniculitis due to exposure to cold, and lupus panniculitis (lupus profundus).

Causes and associations are diverse. Infections (such as streptococcal), medications, autoimmune or inflammatory diseases (for example Crohn’s disease or sarcoidosis), trauma, pancreatitis, and certain metabolic or hematologic conditions can trigger panniculitis. In many cases, no single cause is identified.

Diagnosis relies on clinical evaluation supported by a skin biopsy to determine the pattern of inflammation, along with laboratory tests to identify underlying triggers. Imaging or additional tests may be used when systemic disease is suspected.

Treatment focuses on the underlying cause and symptom control. Many forms resolve with treatment of the trigger and supportive care, such as analgesia and compression for nodules. Corticosteroids or other therapies may be considered for persistent, extensive, or vasculitic panniculitis. Prognosis varies with the type and underlying condition, with erythema nodosum often self-limiting.