Paroxysmal nocturnal hemoglobinuria (PNH)

Definition

Paroxysmal nocturnal hemoglobinuria is a rare, acquired disorder of blood cells in which a specific molecule on the surface of the cells leads to premature destruction of the cells. This destruction is intermittent (paroxysmal).

Causes, incidence, and risk factors

PNH is caused by a defect in the formation of a protein anchor called GPI. As a result of the lack of certain surface proteins, a number of surface proteins are unable to remain tethered to the cell surface, including the proteins CD55, also called Decay Accelerating Factor (DAF), and CD59, also called Membrane Inhibitor of Complement Lysis (MIRL).

A result of the loss of these cell-surface proteins is an enhanced sensitivity to complement-mediated cell destruction. (Complement is a substance produced by the immune system.) The disease can affect people of any age.

Red blood cell, white blood cell, and platelet counts may be low. Urine may be intermittently red or brown, signifying the breakdown of red blood cells with release of hemoglobin into the circulation and then the urine.

Blood clots may form in some people. The disease may arise in relation to aplastic anemia, and may progress to acute myelogenous leukemia. Risk factors, except for prior aplastic anemia, are not known.

Symptoms

• intermittent dark urine
• abdominal pain
• back pain
• headache
• shortness of breath
• easy bruising or bleeding in the skin

Signs and tests

• CBC may show low white blood cell count, red blood cell count, and platelets
• sucrose hemolysis test is positive
• Ham's (acid hemolysin) test is positive
• Flow cytometry shows a lack of specific surface proteins
• urinalysis shows hemosiderin and hemoglobin
• serum hemoglobin results may be altered

Treatment

Steroids may be effective in suppressing hemolysis (cell destruction). Blood transfusions may be required. Anticoagulation therapy may also be required to prevent clot formation.

Bone marrow transplantation can cure this disease.

Expectations (prognosis)

The outcome is variable, with most people surviving approximately 10 years following diagnosis. In rare cases, the abnormal cells may decrease over time. Death can be caused by complications of blood clot formation (thrombosis) or by infection or bleeding due to a lack of normal blood cells.

Complications

• blood clots
• anemia 
• acute myelogenous leukemia
• iron deficiency anemia
• death

Calling your health care provider

Call your health care provider if you find blood in your urine, if symptoms worsen or do not improve with treatment or if new symptoms develop.

Prevention

There is no known way to prevent this disorder.

Illustrations

Blood cells

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