Hematology · USMLE Step 1 and Step 2

Sideroblastic Anemia song

Sideroblastic Anemia - Causes & Smear, as a song. Hear the short teaser here. The full song is on YouTube and Spotify.

Sideroblastic Anemia

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Key points in this song10

Sideroblastic anemia is characterized by ringed sideroblasts on Prussian blue stain — iron-laden mitochondria surrounding the nucleus of erythroblasts in a perinuclear ring pattern.
The most common acquired cause is chronic alcohol use, which disrupts heme synthesis by inhibiting pyridoxal-5-phosphate (active B6) and directly impairing ALA synthase.
Isoniazid (INH) causes sideroblastic anemia by antagonizing pyridoxine (B6), which is a required cofactor for ALA synthase — the rate-limiting enzyme of heme synthesis.
Labs show a microcytic, hypochromic anemia with elevated serum iron, elevated ferritin, elevated transferrin saturation, and normal to low TIBC — distinguishing it from iron deficiency anemia.
X-linked sideroblastic anemia is caused by mutations in ALAS2 (ALA synthase 2), the erythroid-specific isoform located on the X chromosome, and responds to high-dose pyridoxine.
Myelodysplastic syndrome (MDS) with ring sideroblasts is the classic acquired clonal cause, associated with SF3B1 mutations, and carries a risk of transformation to AML.
In sideroblastic anemia, the RBC distribution width (RDW) is classically elevated due to a dimorphic smear — a mix of normal and hypochromic microcytic red cells.
Lead poisoning causes sideroblastic anemia by inhibiting ALA dehydratase and ferrochelatase, blocking heme synthesis at two steps, and is associated with basophilic stippling on peripheral smear.
Treatment of reversible causes: discontinue alcohol or offending drug; pyridoxine supplementation treats INH-induced and X-linked forms; chelation therapy for lead toxicity.
Unlike iron deficiency anemia, sideroblastic anemia presents with iron overload — repeated transfusions worsen hemosiderosis, and chelation with deferoxamine may be required.