A 35 year old lady is admitted with pyrexia, weight loss, diarrhea and her skin is lemon yellow in color. CBC = high MCV. What is the most probably diagnosis?

The key is B. Pernicious anemia. [It may be graves disease with pernicious anemia. Lemon yellow pallor occurs in pernicious anemia. Both are autoimmune disease which favours this association. Hyperthyroidism may cause persistently raised body temperature, weight loss and diarrhea. In pernicious anemia there is lack of intrinsic factor which is needed to absorb vitamin B12 and as this vitamin is not absorbed in pernicious anemia there occurs macrocytic anemia that leads to high MCV].