Snapshot A 26-year-old man presents to his primary care physician for an abnormal skin rash in his legs. The skin rash is found bilaterally at the level at the tibia. He says that the rash appears red and is warm to the touch. He denies any recent trauma to his lower extremities. Medical history is significant for ulcerative colitis. Physical examination is notable for bilateral erythematous nodules that are slightly raised. These lesions are warm to the touch and are tender to palpation. (Erythema nodosum) Introduction Definition subcutaneous fat inflammation Epidemiology Incidence erythema nodosum is the most common type of panniculitis Etiology Inflammatory erythema nodosum lupus panniculitis cutaneous polyarteritis Infectious Traumatic Deposition gout calciphylaxis Malignancy cutaneous lymphoma Presentation Symptoms/physical exam of note, there are various forms of panniculitis ulcers atrophy sclerosis livedo racemosa can be tender to palpation Studies Skin biopsy indication in cases where the diagnosis is unclear or the diagnosis needs to be confirmed Treatment Note that the mainstay of treatment is treating the underlying cause of the panniculitis