History

• Fever, malaise, chills, fatigue
• Increasingly tender and aching patches on the legs, mainly below the knee.
• Eruptions often preceded by symptoms of pharyngitis or other upper respiratory infection
• Headache
• Arthralgias (rare)

Physical Exam

• Initially warm, tender, brightly erythematous nodules, which may be raised, on anterior shins. Lesions become bluish and fluctuant, gradually fading to yellowish resembling a bruise.
• Can also occur on any area with subcutaneous fat
• Diameter 1–15 cm

Lab

• Elevated ESR
• CBC: Mild leukocytosis
• Antistreptolysin titers maybe elevated.
• Throat culture (usually negative because the infection typically resolves before lesions appear)
• Stool culture and leukocytes, if indicated
• Skin testing for mycobacteria, if indicated
• Drugs that may alter lab results: Antecedent antibiotics may affect cultures.

Imaging
CXR for hilar adenopathy or infiltrates related to sarcoidosis or tuberculosis

Diagnostic Procedures/Other
Deep skin excisional biopsy including subcutaneous fat; rarely necessary.

Pathological Findings

• Septal panniculitis
• Neutrophilic infiltrate in septa of fat tissue, early in course
• Fibrosis, paraseptal granulation tissue, lymphocytes, and multinucleated giant cells predominate late in course
• Lower dermis/subcutis involvement and septal fibrosis may occur.

• Superficial thrombophlebitis
• Cellulitis
• Septic emboli
• Erythema induratum (ulcerating calf nodules)
• Nodular vasculitis (warm, ulcerating nodules)
• Weber-Christian disease (violaceous, scarring nodules)
• Lupus panniculitis
• Cutaneous polyarteritis nodosa
• Sarcoidosis granulomata
• Cutaneous T-cell lymphoma
• Erythema nodosum leprosum