Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disorder characterized by intravascular hemolysis and hemoglobinuria, the latter accentuated during sleep. Leukopenia, thrombocytopenia, and episodic crises are common. Diagnosis requires flow cytometry. Treatment is supportive.
PNH is most common among men in their 20s, but it occurs in both sexes and at any age.
PNH is an acquired genetic mutation resulting in a membrane defect in stem cells and their progeny, including RBCs, WBCs, and platelets. It results in unusual sensitivity to normal C3 in the plasma, leading to ongoing intravascular hemolysis of RBCs and diminished marrow production of WBCs and platelets. The defect is a missing glycosyl-phosphatidyl-inositol anchor for membrane proteins caused by an abnormality of the PIG-A gene, which is located on the X chromosome.
Protracted urinary Hb loss may result in iron deficiency. Patients are strongly predisposed to both venous and arterial thrombi, including the Budd-Chiari syndrome. Thrombi are commonly fatal. Some patients with PNH develop aplastic anemia, and some with aplastic anemia develop PNH.
Crises may be precipitated by infection, iron use, vaccination, or menstruation. Abdominal and lumbar pain and symptoms of severe anemia may occur; gross hemoglobinuria and splenomegaly are common.
PNH is suspected in patients who have typical symptoms of anemia or unexplained normocytic anemia with intravascular hemolysis, particularly if leukopenia or thrombocytopenia is present. Historically, if PNH was suspected, the sugar-water test was usually the first test done; it relies on enhanced hemolysis of C3-dependent systems in isotonic solutions of low ionic strength, is simple to do, and is sensitive. However, the test is nonspecific; positive results require confirmation by further testing. The most sensitive and specific test is determination of the absence of specific RBC or WBC membrane proteins (CD59 and CD55) by flow cytometry. An alternative is the acid hemolysis test (Ham's test). Hemolysis usually occurs if blood is acidified with HCl, incubated for 1 h, and centrifuged. Bone marrow examination is not necessary but, if done to exclude other disorders, usually shows marrow hypoplasia. Gross hemoglobinuria is common during crises, and the urine may contain hemosiderin.
Treatment is largely symptomatic. However, a new monoclonal antibody that is a terminal complement inhibitor, eculizumab, has reduced transfusion requirements, thromboembolism, and symptoms. Supportive measures include corticosteroids, androgen hormones, iron and folate supplementation, and sometimes transfusions and stem cell transplantation. Empiric use of corticosteroids (eg, prednisone 20 to 40 mg po once/day) controls symptoms and stabilizes RBC values in > 50% of patients. Androgenic hormones and recombinant erythropoietin to stimulate hematopoiesis have been used in some patients. Generally, transfusions are reserved for crises. Transfusions containing plasma (and C3) should be avoided. Washing RBCs with saline before transfusion is no longer necessary. Heparin followed by warfarin may be required for thromboses but should be used cautiously. Oral iron and folate supplements may be necessary. Most cases can be managed by these supportive measures for years to decades. Allogenic stem cell transplantation has been successful in a small number of cases.
Last full review/revision February 2009 by Alan E. Lichtin, MD
Content last modified February 2012