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Diagnostic Pearls

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Differential Diagnosis & Pitfalls

• Erythema nodosum – Tender bilateral, symmetric, self-limited nodules, usually preceded by an identifiable infection, autoinflammatory condition, or medication. 
• Nodular vasculitis (erythema induratum) 
• Pancreatic panniculitis 
• Alpha-1 antitrypsin deficiency panniculitis 
• Lupus panniculitis – Tender plaques and nodules most commonly affect the upper body of patients with systemic lupus erythematosus. 
• Cytophagic histiocytic panniculitis – Nodules tend to ulcerate and drain, and biopsy reveals lobular panniculitis with "beanbag" cells. 
• Lipodermatosclerosis – Signs and symptoms of venous insufficiency, including varicose veins, edema, and atrophic skin. 

• Subcutaneous panniculitis-like T-cell lymphoma – Skin lesions may be almost identical to SNMP, but immunohistochemical studies will reveal neoplastic T-cells. 
• Polyarteritis nodosa – Lower extremity nodules are commonly associated with livedo reticularis. Biopsy reveals medium-vessel vasculitis and inflammation limited to the perivascular zones. 
• Necrobiosis lipoidica 
• Morphea 
• Subcutaneous granuloma annulare  
• Rheumatoid nodule – Nontender nodules located on extensor and pressure surfaces of patients with rheumatoid arthritis. 
• Sarcoidosis  
• Superficial migratory thrombophlebitis – Tender nodules develop along course of a vein with associated thrombosis. 
• Arthropod bites

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