Paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is an acquired haematopoietic stem cell disorder whereby some of the red blood cells produced are defective and are susceptible to premature destruction by the immune system, leading to haemoglobinuria.

Terminology

The term comes from a mistaken 19^th century belief that the haemolysis and subsequent haemoglobinuria occurred only intermittently (paroxysmally) and with greater frequency during the night (nocturnal). Haemoglobinuria is most prominent in the morning after the urine has concentrated overnight during sleep but haemolysis in paroxysmal nocturnal haemoglobinuria is a constant process.

Epidemiology

Prevalence is low, at 1-10 per 1,000,000. No difference in prevalence between the the sexes has been found, M:F = 1:1. Median age at diagnosis is in the fourth decade ^ref2.

Clinical presentation

• anemiaanaemia
• profound fatigue
• stress dyspneadyspnoea
• haemoglobinuria
• dysphagia
• abdominal pain
• erectile dysfunction

Pathology

Paroxysmal nocturnal haemoglobinuria is caused by a defect in surface proteins of red blood cells, typically due to an acquired mutation in the PIGA gene on the X chromosome in a haematopoietic stem cell ^1,7. These surface proteins usually protect red blood cells and other immune cells from destruction via the complement system, thus a defect in these proteins increases their destruction, leading to the aforementioned clinical presentation ¹.

In addition to the anaemia from haemolysis, patients suffer from the direct effects of intravascular haemolysis that results in the absorption of nitric oxide, a key molecule in homeostasishomoeostasis, leading to smooth muscle dysfunction and platelet activation, markedly raising the risk of thrombosis ¹.

Radiographic features

Ultrasound, CT and MRI may show features of thrombosis of major vessels, particularly in the abdomen.

Rarely thrombosis of smaller vessels may cause osteonecrosis of the femoral head.

Treatment and prognosis

• blood transfusions
• anticoagulation
• bone marrow transplant ¹
• eculizumab ¹

ApproximatelyWithout therapy approximately 50% of patients die as a direct result of the disease. Many others are transfusion dependentdependant for decades ^ref3.

Pregnancy results in extremely high risk for maternal and fetal mortality, predominantly resulting from thrombotic complications ^ref4.

Eculizumab has been shown by recent data to prevent most of the complications and significantly improves survival ^ref2,5,6.

Complications

Common

• thrombosis
• renal impairment
• pulmonary hypertension

Rare

• bone marrow failure
• myelodysplasia,
• acute leukemialeukaemia
• renal haemosiderosis
• osteonecrosis (avascular necrosis): hip