2025 – PAGE 283 – HEMATOLOGY & ONCOLOGY
PYRUVATE KINASE DEFICIENCY
Pyruvate kinase deficiency is an enzyme deficiency resulting in energy issues we will not discuss here. The end result is an unstable RBC structure, causing RBC deformities and hemolysis. The hemolytic anemia can cause hyperbilirubinemia and jaundice.
PEARL: One of the metabolites that builds up due to the PK deficiency is 2,3-diphosphoglycerol (DPG). DPG causes the oxygen dissociation curve to shift to the right, resulting in the hemoglobin having less O2 affinity. So the patient can have a surprisingly good exercise tolerance even though he or she is anemic.
IMAGE: www.pbrlinks.com/PYRUVATE1
MNEMONIC: Some people know the DPG as Snoop’s “Dog Pound Gang.” Now imagine Snoop and his gang having surprisingly good exercise tolerance. Given how much they smoke, it truly would be impressive.
MNEMONIC VIDEO: www.pbrlinks.com/PYRUVATE2
HEREDITARY SPHEROCYTOSIS
Look for intermittent anemia and possibly a similar family history to diagnose hereditary spherocytosis. It’s an inherited disorder resulting in spectrin deficiency (usually autosomal dominant). Cells are more fragile and, as pieces of the RBC membrane are ripped off, spherical cells are left behind. The amount of hemoglobin remains the SAME in this slightly smaller, spherical cell. The results is an ELEVATED MCHC. Diagnose with osmotic fragility testing. Treat with folic acid and transfusions (when needed).
PEARLS: Parvovirus B19 can cause an aplastic crisis. While HS patients usually have an elevated retic count due to their ongoing hemolysis, the count will be low in an aplastic crisis. The resulting constellation of lab values is extremely unique: LOW hemoglobin + LOW reticulocyte count + HIGH MCHC. If you see this combination on the pediatric boards, select HS with aplastic crisis.
MNEMONICS: HS = HS. Hereditary SpherOcytOsis = Hereditary Spectrin deficiency. SpherOcytOsis = OsmOtic fragility testing.
(DOUBLE TAKE) ERYTHEMA INFECTIOUSUM
Erythema infectiosum IS an INFECTIOUS rash!!! It is caused by Parvovirus B19. It is also called Fifth Disease Look for erythematous facial flushing of the cheeks (sometimes described as “slapped cheeks” appearance). The extremities will have diffuse macular (or morbilliform) erythema (especially on the extensor surfaces) referred to as “lacy” or “reticular.” Diagnose with IgM titers. (There is no culture or rapid antigen available.)
PEARLS: The rash occurs AFTER the slapped cheeks rash (often a week later). Patients may also have knee or ankle pain. Parvovirus B19 infection can result in APLASTIC CRISIS. Intrauterine exposure can result in hydrops fetalis.
MNEMONIC: infectio5uM = FIFTH disease = “Five fingers.” Imagine a cheek being SLAPPED with FIVE fingers covered by a white LACY glove with a red M on the back of it (extensor surface). M = IgM titers.
MNEMONIC: ParVoVirus B19: From now on, say/think “parVoVirus V19.” V = Roman numeral 5!