<prompt> A 25 yr old male having fever malaise since 2 weeks, ahritis of ankle joint and tender erythematous nodules over the shin. Diagnosis is?Erythema nodosumErythema marginatumWeber Christian diseaseUicarial vasculitis  <response>: Erythema nodosum is most common on the shins, but it may also occur on other areas of the body buttocks, calves, ankles, thighs, and arms. The lesions begin as flat, firm, hot, red, painful lumps approximately an inch across. Within a few days they may become purplish, then over several weeks fade to a brownish, flat patch. Other symptoms may include: a. Fever b. General ill feeling malaise c. Joint aches d. Skin redness, inflammation, or irritation e. Swelling of the leg or other affected area. Causes of erythema nodosum infections, such as Streptococcal pharyngitis or strep throat. bacterial infections, such as Mycoplasma pneumonia or tuberculosis. viral infections. deep fungal infections. sarcoidosis. cancer. antibiotics. oral contraceptives Ref Robbins 9e pg 345 