Erythema Nodosum AND Panniculitis — Nodules of the Lower Limb

The answer first

Erythema nodosum and panniculitis are inflammatory reactions of the subcutaneous fat that present as tender nodules, most often on the shins. The single most important physician action is to separate the common, self-limiting septal pattern (classic erythema nodosum) from the lobular, ulcerating, systemic patterns that demand biopsy and a multisystem workup. ^[1]

A consultant-grade answer rests on four pillars: ^[1]

1. Classify the nodules by where the inflammation sits. Erythema nodosum is the prototype septal panniculitis with spared lobules and no vasculitis; everything that ulcerates, scars, suppurates or recurs sits in the lobular group and behaves differently. The clinical pattern predicts histology, but histology — a 5 to 6 mm punch or incisional biopsy reaching subcutaneous fat — changes management. ^[4]
2. Treat erythema nodosum as a reactive pattern, not a disease. In adults the dominant triggers are streptococcal pharyngitis, sarcoidosis (especially Löfgren syndrome), inflammatory bowel disease, pregnancy and drugs (oral contraceptives, sulfonamides, bromides, BRAF inhibitors); a focused history and a short panel resolve most cases without skin biopsy. ^[1]
3. Recognise the dangerous mimics. Erythema induratum (nodular vasculitis) signals tuberculosis; pancreatic panniculitis may be the first clue to pancreatitis or pancreatic carcinoma; alpha-1 antitrypsin deficiency panniculitis ulcerates after minor trauma and demands specific replacement or avoidance of dapsone. ^[4]
4. Stage treatment by severity and cause. Most erythema nodosum resolves in three to six weeks with rest, compression and non-steroidal anti-inflammatory drugs; refractory or relapsing disease warrants a short course of potassium iodide 300 to 900 mg three times daily, or oral corticosteroid (prednisone 0.5 to 1 mg/kg per day) once infection is excluded. ^{[1] [2]}

DWE high-yield: "Ulcerating panniculitis is not erythema nodosum." The triad that should send the patient to biopsy rather than reassurance is ulceration, recurrence and systemic symptoms — these three pivot the diagnosis from benign septal erythema nodosum to the lobular mimics (erythema induratum, pancreatic, alpha-1 antitrypsin deficiency, Weber-Christian) that need a defined systemic workup. ^[4]

References12ShowHide

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11. [11]Miteva M, Romanelli P, Kirsner RS Lipodermatosclerosis. Dermatol Ther, 2010.PMID 20666825
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