An 81-year-old man was admitted for workup of anemia. His red blood cell (RBC) count was 2.6×106/mm3 (2.6 × 1012/L); hemoglobin level, 7.3 g/dL (73 g/L); hematocrit reading, 22.1% (0.22); mean corpuscular volume, 72 μm3; and mean corpuscular hemoglobin level, 24 pg. The peripheral blood smear showed a dimorphic picture, ie, normocytic cells admixed with a preponderantly microcytic-hypochromic RBC population and rare siderocytes. Prussian blue stain of the bone marrow disclosed numerous ringed sideroblasts,1,2 which are erythroblasts with coarse iron granules arranged around the nucleus (Figure). The diagnosis was acquired sideroblastic anemia secondary to isoniazid use.
Sideroblastic anemia is a hematologic disorder that occurs under a variety of circumstances. Rarely is it hereditary, being more commonly an acquired condition. Acquired sideroblastic anemia can be secondary to exposure to certain drugs and toxins. Implicated are antituberculous drugs (with isoniazid the most common offender), antibiotics