Hypocellular marrow involving all elements, often with replacement of bone marrow by fat cells, is characteristic of which disorder?

• A. Iron deficiency anemia
• B. Aplastic anemia
• C. Folate deficiency anemia
• D. Pernicious anemia

Answer: (B)

This pattern reflects bone marrow failure where the hematopoietic stem cell pool is depleted and the marrow is replaced by fat. That is classic for aplastic anemia, in which all blood cell lines are reduced, leading to pancytopenia and a very low reticulocyte count. The marrow biopsy shows markedly decreased cellularity with fat replacement, signaling loss of productive marrow.

Other common anemias don’t typically show this fatty, hypocellular marrow. Folate deficiency and pernicious anemia produce megaloblastic changes with more cellular, not fatty, marrow (often normal to hypercellular). Iron deficiency anemia usually shows compensatory erythroid hyperplasia rather than fatty replacement.