Review Question - QID 102777

The patient is presenting with fatigue and macrocytic anemia (as indicated by the MCV > 100 fL) which is most likely a side effect from taking methotrexate.

Methotrexate interferes with folic acid metabolism and commonly results in macrocytic anemia in patients not taking folate supplements. Methotrexate is a dihydrofolate reductase inhibitor and is indicated in the management of an ectopic pregnancy, in rheumatoid arthritis, and in certain malignancies among many other conditions. Dihydrofolate reductase converts folic acid into a reduced form (FH4-folinic acid) that is essential in the de novo production of thymidine. Patients taking methotrexate are unable to use folate effectively which in turn causes a macrocytic anemia.

Incorrect Answers:
Answer 1: Depression would present with 5 of the SIGE CAPS criteria (Sleep changes, Interest loss, Guilt, Energy loss, Concentration trouble, Appetite changes, Psychomotor retardation, and Suicidality). This patient is only suffering from fatigue, energy loss, guilt, and some interest loss which does not meet criteria for depression and is better explained by her anemia.

Answer 2: Gastrointestinal bleed would present with a microcytic anemia and would warrant further workup with a colonoscopy. The small amount of blood on the toilet paper for this patient is likely from a fissure or external hemorrhoid.

Answer 3: Iron deficiency causes a microcytic anemia, which presents with a low MCV (< 80 fL). It is commonly caused by poor iron intake and bleeding (such as menses or GI bleeds).

Answer 5: Vitamin B12 deficiency can result in a macrocytic anemia but is uncommon unless the patient is an alcoholic, elderly patient, or a vegan.

Bullet Summary:
Methotrexate can cause a megaloblastic anemia.