A patient from Africa comes with nodular patch on the shin which is reddish brown. What is the most probable diagnosis?

The key is B. Erythema nodosum. [Causes of erythema nodosum: MOST COMMON CAUSES- i) streptococcal infection ii) sarcoidosis. Other causes- tuberculosis, mycoplasma pneumonia, infectious mononucleosis, drugs- sulfa related drug, OCP, oestrogen; Behcet’s disease, CD, UC; lymphoma, leukemia and some others].