This video provides a detailed explanation of Paroxysmal Nocturnal Hemoglobinuria (PNH), an acquired chronic hemolytic anemia. It covers the underlying PI gene mutation in myeloid stem cells, leading to a deficiency in GPI-anchored proteins (CD55 and CD59) that regulate the complement system. The video elucidates the alternative pathway of complement activation and how the absence of CD55 and CD59 results in the complement system attacking and destroying red blood cells, causing intravascular hemolysis. Complications, clinical presentation (hemolytic anemia, pancytopenia, venous thrombosis), lab findings, diagnosis (flow cytometry), and treatment options (iron/folate, RBC transfusion, contraindication of glucocorticoids, eculizumab, stem cell transplant) are also discussed.
Understanding Paroxysmal Nocturnal Hemoglobinuria (PNH): A Comprehensive Overview
0:00 Definition: PNH is an acquired chronic hemolytic anemia characterized by episodic hemoglobinuria (hemoglobin in the urine) at night.
0:15 Pathophysiology: The disease is caused by a mutation in the PI gene within myeloid stem cells, which normally give rise to red blood cells, neutrophils, and platelets. This mutation is acquired after birth, not inherited.
0:21 PI Gene Mutation: The PI gene (phosphatidylinositol glycan anchor biosynthesis class A) encodes an enzyme responsible for synthesizing membrane-associated proteins that regulate the complement system.
0:41 Complement Regulatory Proteins: Specifically, the PI gene mutation leads to a deficiency in glycosylphosphatidylinositol (GPI), which acts as an anchor for complement regulatory proteins CD55 (decay-accelerating factor) and CD59 (membrane inhibitor of reactive lysis).
2:57 Alternative Complement Pathway: In PNH, the issue typically arises in the alternative pathway of the complement system, triggered by bacterial endotoxins (lipopolysaccharides).
4:03 Complement and Cell Destruction: Without CD55 and CD59, the complement system cannot differentiate between "self" and "non-self." It attacks and destroys normal blood cells (red blood cells in particular), leading to intravascular hemolysis.
6:39 Hemoglobinuria: The destruction of red blood cells releases hemoglobin into the urine, causing it to appear darker, especially in the first morning sample due to increased urine concentration.
7:05 Complications: Complications of PNH include iron deficiency anemia (due to hemoglobin loss in urine), acute myeloid leukemia, and thrombosis (especially venous).
7:54 Clinical Triad: The classic clinical presentation involves hemolytic anemia, pancytopenia, and venous thrombosis. Symptoms depend on the location of venous thrombosis, such as hepatic veins (Budd-Chiari syndrome).
8:54 Lab Findings: CBC reveals decreased hemoglobin and hematocrit (anemia), increased reticulocytes (response to hemolysis), usually normal MCV (but can be low with iron deficiency or high with reticulocytosis), high LDH, high unconjugated bilirubin, and low haptoglobin. Direct Coombs test is negative.
10:36 Diagnosis: Flow cytometry is the gold standard for diagnosis, detecting the absence of CD55 and CD59. Sucrose hemolysis and acidified serum (Ham's) tests are less reliable.
10:43 Treatment: Treatment includes iron and folate supplementation, RBC transfusions for severe anemia. Glucocorticoids are generally contraindicated.
10:51 Eculizumab: Eculizumab, a monoclonal antibody targeting C5, reduces mortality by preventing the formation of the membrane attack complex (MAC). Vaccination against Neisseria meningitidis is essential when using eculizumab.
11:40 Definitive Treatment: Stem cell transplantation is the definitive treatment.