Last updated: November 4, 2014

Synonyms: Erythema nodosum, Weber-Christian disease.

ICD-9 Code: 729.30.

ICD-10 Code: M79.3

Definition: Panniculitis is inflammation within subcutaneous fat.

Etiology: Panniculitis can be caused by a variety of systemic diseases and is classified according to histopathologic criteria in four major groups: septal, lobular, mixed, and with vasculitis (Table 30). Panniculitis seldom occurs in association with hypersensitivity vasculitis or PAN. The pathogenesis involves a dynamic process of inflammation evolving from a neutrophilic infiltrate to eventual fibrosis.

Table 30
Major Types of Panniculitis
Disease Hisologic Substype Peak Age M:F Ratio Key Features
Erythema nodosumWeber-Christian diseaseLupus Panniculitis (lupus Profoundus) SeptalLobularMixed  25-40
1:33:71:9 Acute process,anterior tibia; resolves without scarringFever, multiple sites, visceral involvementLesions on face, upper arms, buttocks, breasts; may ulcerate with scarring

Pathology: Skin/fat biopsy findings reflect the age of the lesion. Neutrophils are seen early, followed by macrophage infiltration and the formation of granulomata. Fibrosis is seen late.

Demographics: Panniculitis is rare; prevalence is less than one per 100,000. It occurs in the third to fifth decades (Table 30).

Cardinal Findings: Features common to all panniculitides include tender subcutaneous nodules. Associated phenomena are common and depend on the underlying clinical syndrome. In erythema nodosum, tender nodules appear on the anterior tibial surface and evolve into ecchymotic lesions that typically regress in 4 to 6 weeks without scarring. Weber-Christian disease is characterized by multiple recurrent subcutaneous nodules, fever, arthralgia, myalgia, and occasional abdominal pain; eventually fibrosis occurs. Lupus erythematosus panniculitis (lupus profundus) is seen in less than 3% of patients with SLE, with tender nodules that may ulcerate occurring on the face, arms, buttocks, or breasts. In PAN, small vessel vasculitis may cause panniculitis. Some patients with pancreatic disease develop subcutaneous fat necrosis (lobular panniculitis) with polyarthritis. Lobular panniculitis has also been associated with a1-antitrypsin deficiency.

Keys to Diagnosis: Panniculitis should be suspected with tender subcutaneous nodules that are often red and may turn violaceous. Fibrosis is seen in late cases. Ulceration is rare.

Diagnostic Tests: Choice of tests depends on the clinical picture but may include pharyngeal culture for streptococcal infection, chest radiograph, skin test for tuberculosis, and serum tests for amylase, lipase, and a1-antitrypsin. Skin/fat biopsy is usually not necessary to diagnose erythema nodosum but may be helpful in other forms of panniculitis.

Therapy: Therapy is directed at underlying disease, if detected. In idiopathic cases, management is symptomatic: bed rest and elevation of extremity (if involved). NSAIDs may be useful, and oral corticosteroids are effective in most. Immunosuppressive agents are reserved for recurrent/ recalcitrant disease.

Prognosis: Prognosis depends on underlying disease. Most cases of erythema nodosum resolve in 4 to 6 weeks. Weber-Christian disease is typically chronic, with death in 10% to 15% of cases. In lupus profundus, the course often does not follow systemic disease activity.

Callen JP. Miscellaneous disorders that commonly affect both skin and joints: panniculitis. In: Sontheimer RD, Provost TT, eds. Cutaneous manifestations of rheumatic diseases. Baltimore: Williams & Wilkins, 1996:266–273.

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