This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pathology
A 25 yr old male having fever & malaise since 2 weeks, ahritis of ankle joint and tender erythematous nodules over the shin. Diagnosis is? 
Select and explain. 
A. Erythema nodosum, B. Erythema marginatum, C. Weber Christian disease, D. Uicarial vasculitis
A: Erythema nodosum
Answer: A: Erythema nodosum 
Explanation: 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 9/e pg 345