Sideroblastic anemias are a heterogeneous group, that share the following common features: the occurrence of ringed sideroblasts in the bone marrow, ineffective erythropoiesis, an elevated serum iron and mostly macrocytic erythrocytes. Sometimes, the erythrocytes are normocytic or microcytic. In the blood film, the population of erythrocytes can be dimorphous, i.e. normochromic macrocytes and hypochromic microcytes are seen. There are inherited and acquired forms. The latter are in turn subdivided into primary forms (belonging to the myelodysplastic syndromes) and secondary forms (drug-induced or chronic inflammatory diseases).
Symptoms are similar to those of anemia. Hereditary forms usually manifest themselves in the first months to years of life, while the acquired primary form typically occurs only in the elderly. Drugs that typically induce sideroblastic anemia include isoniazid, pyrazinamide and cycloserine.
The hereditary forms often demonstrate hypochromia, marked anisocytosis and poikilocytosis. In the acquired forms, microcytosis as well as macrocytosis can be observed.
Ringed sideroblasts (right image) are found in bone marrow stained with Prussian blue. These are normoblasts with hemosiderin granules arranged around the nucleus (see also sideroblasts = left image). They constitute more than 15% of the marrow normoblasts.