Panniculitides

Abstract

Panniculitis is an inflammation that originates primarily in the subcutaneous fatty tissue (panniculus adiposus). It is associated with rheumatological diseases and with adverse events to rheumatological therapies (e.g. poststeroid panniculitis, erythema nodosum, infective panniculitis). The panniculitides are classified histopathologically into mostly septal panniculitis and mostly lobular panniculitis, according to the major or denser localization of the infiltrate, and also into those with or without vasculitis. Additional criteria involve the composition of the inflammatory infiltrate, the cause, and an underlying or associated disease. The clinical hallmarks of panniculitis are subcutaneous nodules or plaques, often located on the lower limb. A deep excisional biopsy is often required for a more precise diagnosis, given the often sparse and monotonous clinical symptoms. Erythema nodosum is the most common form and a typical example of septal panniculitis. It occurs in response to many different provoking factors, the most common trigger in children being a ’strep throat’, in adults sarcoidosis. Clinically, it presents with a sudden symmetrical appearance of painful, tender, warm, erythematous nodes or plaques, usually on the shins, which resemble bruises. Classical and cutaneous polyarteriitis nodosa present a mostly septal panniculitis associated with vasculitis. Here subcutaneous, partially ulcerating nodules are surrounded by livedo racemosa. The mostly lobular panniculitides not associated with vasculitis include lupus panniculitis (lupus erythematosus profundus, typically with ensuing lipoatrophy and predilection for the upper part of the body), panniculitis in dermatomyositis (often calcifiying), cold panniculitis, pancreatic panniculitis, panniculitis due toα‎‎-antitrypsin deficiency, poststeroid panniculitis (in children after rapid withdrawal of corticosteroids), calciphylaxis (with and without renal failure), and factitious panniculitis (after mechanical, physical, or chemical injuries to the subcutaneous tissue, often self-inflicted). Nodular vasculitis (formerly erythema induratum Bazin) is a lobular panniculitis with vasculitis involving mostly the small blood vessels of the fat lobule. It appears to present a (hyper)reactive response to certain infections (tuberculosis, streptococci, candida) or to cold exposure or chronic venous insufficiency in susceptible females. In conclusion, the panniculitides are a heterogenous group of diseases requiring a systematic work-up and knowledge of certain histological or clinical criteria.