Snapshot A 25-year-old woman with a history of sarcoidosis presents with fever, fatigue, and joint pain over the past week. Yesterday, she developed a bruise-like and raised painful rash on her shins despite having no recent trauma to the area. Physical exam reveals multiple 2-4 cm erythematous and tender nodules with poorly demarcated borders on her anterior shins. Laboratory examination reveals elevated inflammatory markers. She is sent home with reassurance and instructions to take ibuprofen as needed for pain. Introduction Clinical definition a panniculitis characterized by painful subcutaneous nodules typically located on pretibial surfaces Associated conditions infection coccidioidomycosis (desert bumps) histoplasmosis tuberculosis streptococcus leprosy Behcet syndrome Sweet syndrome inflammatory bowel disease sarcoidosis Epidemiology Incidence the most common panniculitis Demographics female > male peak incidence between 20-30 years of age Risk factors infection autoimmune disease leprosy ETIOLOGY Pathogenesis some evidence suggests type IV delayed hypersensitivity response immune complex deposition in venules of connective tissue or subcutaneous fat, causing subcutaneous nodules Presentation Symptoms sudden onset painful symmetric rash often preceded by inflammation/infection may be preceded by prodrome fever, malaise, and fatigue arthralgia Physical exam warm and erythematous subcutaneous nodules that are 1-10 cm in diameter tender to palpation poorly demarcated margins location typically symmetrically on anterior shins can also affect forearms, thighs, trunk, head, or neck Studies Labs ↑ inflammatory markers erythrocyte sedimentation rate C-reactive protein Biopsy indications only if diagnosis is unclear clinically Histology septal panniculitis without vasculitis septa is thickened and has inflammatory infiltration Differential Scleroderma Granulomas Treatment Management approach treat underlying cause Medical nonsteroidal anti-inflammatory drugs (NSAIDs) indication for symptomatic relief as needed Complications Arthralgias may persist Secondary bacterial infection Prognosis Erythema nodosum typically resolves spontaneously and fades over 1-2 months