This is a case report of a patient with resistant erythema nodosum. Despite multiple traditional treatments, the patient did not improve until the use of potassium iodide, an under used treatment for EN. Also included is a review of EN including clinical features, histology, and treatment. Potassium iodide as a treatment for treatment resistant EN is discussed in detail including possible mechanism of action, dosage, adverse effects, and contraindications. Keywords: Nodules; Potassium iodide; Erythema nodosumAbbreviations EN: Erythema Nodosum; KI: Potassium Iodide Case ReportA 55 year-old Caucasian female with a past medical history of refractory hepatitis C, coronary artery disease, COPD, diabetes, hypertension, obesity, and GERD who presented to our Rheumatology clinic in January complaining of lesions on her right leg.Her lesions started nine months prior as a small spot over her right calf which subsequently grew into nodules. They were tender to touch and red in appearance. She was treated by her primary care physician for cellulitis with several courses of antibiotics including doxycyline without improvement. She was then treated with steroids with no change. She was started on colchicine, which did not help.Her outside labs were reviewed, which included a rheumatoid factor, sedimentation rate, serum protein electrophoresis, complete blood count, creatinine, ANCA, compliment levels including (CH50, C3, C4), C-reactive protein, lyme test, and ANA which were all negative or within normal limits. Her liver enzymes were elevated as well as her angiotensin converting enzyme at 93 with normal being less than 68. An X-ray of her chest was unremarkable. She denied signs or symptoms consistent with connective tissue disease or systemic vasculitis. She denied fevers, weight loss or joint pain. On this initial visit, her physical exam was unremarkable with the exception of several nodules located on her shins, which were tender to palpation, erythematous and ranged in size from 1-5 cm. A clinical diagnosis of erythema nodosum was made and she was started on Dapsone. Hydroxychloroquine was considered but there was concern for liver toxicity with Hepatitis-C.Initially, her nodules decreased in size on Dapsone, but she then developed new nodules on her ankles. She continued to have normal inflammatory markers and elevated liver enzymes on repeat labs. Dapsone was discontinued secondary to the development of lesions while on this medication. Prednisone was started at a low dose of 5 mg daily. She tolerated low dose prednisone but did not have improvement. Her dose was increased to 10 mg daily, but she continued to develop new lesions.She was referred to dermatology who tried high dose steroids beginning at 60 mg with taper over the next two weeks but the nodules did not respond. She was started on a non-steroidal anti-inflammatory, Mobic 7.5 mg daily, at our clinic without improvement. Dermatology then arranged for a biopsy. Biopsy was completed in September 2008 from a large extensor surface nodule of 5 cm on th...