spur cell

**Definition:** Spur cells = acanthocytes (Greek "akantha" = thorn). They are dense, contracted RBCs with a few (2–20) irregularly distributed projections of varying length and width, often with no central pallor. Do not confuse with echinocytes (burr cells).

**Spur cell vs. burr cell (high-yield distinction):** - Acanthocyte (spur cell): few, irregular, unevenly spaced, thorn-like spicules of variable length and thickness. - Echinocyte (burr cell): 10–30 short, evenly spaced, uniform projections, with preserved central pallor. Often an artifact, or seen in uremia, pyruvate kinase deficiency, and after transfusion of stored blood.

**Pathophysiology:** - *Liver disease (spur cell anemia):* Cholesterol-rich lipoproteins (abnormal LDL/lipoprotein X) increase the RBC membrane cholesterol:phospholipid ratio. This lowers membrane fluidity. The cells become rigid and spiculated. The spleen then remodels and sequesters them (extravascular hemolysis), causing a Coombs-negative hemolytic anemia. - *Abetalipoproteinemia (Bassen-Kornzweig):* There is an autosomal recessive defect in microsomal triglyceride transfer protein (MTP). Apolipoprotein B-48 and B-100 cannot be assembled, so chylomicrons, VLDL, and LDL are absent. The abnormal membrane lipid composition produces acanthocytes. - *McLeod syndrome (X-linked, XK gene) and chorea-acanthocytosis (VPS13A):* Neuroacanthocytosis syndromes. - Others: anorexia nervosa/severe malnutrition, hypothyroidism, post-splenectomy, and some cases of vitamin E deficiency.

**Clinical features by association:** - *Cirrhosis/severe alcoholic liver disease:* Spur cell hemolytic anemia is a marker of advanced disease and poor prognosis, with a high short-term mortality. Splenomegaly from portal hypertension worsens it. Definitive therapy is liver transplantation. Splenectomy has been used but is risky. - *Abetalipoproteinemia:* Presents in infancy with fat malabsorption (steatorrhea, failure to thrive), then fat-soluble vitamin deficiency (A, D, E, K). Vitamin E deficiency causes spinocerebellar ataxia, loss of proprioception/vibration (posterior column), and areflexia (Friedreich-like). Vitamin A deficiency causes retinitis pigmentosa. Vitamin K deficiency causes coagulopathy. Very low cholesterol and triglycerides. Biopsy shows intestinal enterocytes with lipid accumulation (lipid-laden, vacuolated). Treatment: low-fat diet and high-dose fat-soluble vitamins, especially vitamin E. - *McLeod syndrome:* Absent Kx antigen with weak Kell antigen expression. It causes chorea, neuropathy, cardiomyopathy, and elevated CK. Transfusion compatibility is an issue.

**Lab/smear findings:** Normocytic anemia, elevated reticulocytes, indirect bilirubin, and LDH, with low haptoglobin, negative Coombs test, and acanthocytes on smear.

**Board pearls:** - "Spur cells + cirrhosis" = Coombs-negative hemolysis from altered membrane cholesterol. - "Child with steatorrhea + ataxia + acanthocytes + low cholesterol" = abetalipoproteinemia (MTP defect). - Spur cell = irregular projections; burr cell = regular projections.