- Infections: bacterial→ strep, mycoplasma; Viral→ hep b, EBV; Fungal→ cocci, blasto, histoplasmosis; mycobacterial→ TB
- Meds: OCPs, bactrim, other
- Autoimmune/Idiopathic: sarcoid, IBD, Bechets dz, other/idiopathic
- Cancer: lymphoma, AML
- Acute, red, nodular, painful erruption
- Sometimes f, fatigue, arthralgias
- Erythematous, painful nodules