Paroxysmal Nocturnal Haemoglobinuria


Paroxysmal Nocturnal Haemoglobinuria


§   Haemolytic anaemia (intravascular)

§   Thrombosis

§   Pancytopenia



§   Somatic mutation in X-linked gene PIG-A (over 100 mutations described, most result in frameshift).

§   Can arise de novo or from acquired aplastic anaemia (up to 70% of AA patients have a PNH clone)

§   Occasionally found in MDS patients

§   Results in deficiency of glycosylphosphatidylinositol anchored proteins (GPI-AP) which binds many proteins to the cell surface including CD59 and CD55. (Lots of other proteins involved in GPI-AP synthesis but they are all encoded by autosomes therefore PIG-A is the only one implicated in PNH).

§   Rare cases of healthy individuals who have PIG-A mutations suggest that they are not sufficient to cause PNH although they are necessary.  Subsequent data suggests that these occur in colony forming units in healthy individuals as opposed to stem cells (as in PNH).

§   CD55 & 59 protects the cell from being lysed by the membrane attack complex. Membrane cofactor protein also helps prevent lysis – this is present on platelets and white cells (which therefore have some protection) but not on red cells.

§   Intravascular red cell lysis leads to large amounts of free Hb in the plasma, which leads to increased consumption of nitric oxide resulting in abdominal pain, oesophageal spasm, erectile dysfunction and possibly thrombocytosis (as well as haemoglobinuria).

§   Chronic haemolysis = activation of complement via the alternative pathway

§   Acute = brisk activation of complement by the classical pathway (Ag-Ab)


Clinical Features

§        Haemolysis

§        Fatigue

§        Jaundice

§        Haemoglobinuria

§        Acute exacerbations at times of infection

§        Tendancy to thrombosis

§        40% have a thrombosis at some point

§        Unusual sites, eg portal vein, hepatic vein (Budd-Chiari)

§        Major cause of death

§        Pancytopenia – especially if associated with aplastic anaemia

§        Tendancy to renal failure

§        Renal vein thrombosis

§        ATN – pigment nephropathy, haemoglobinuria, reduced renal perfusion (Low Hb), tubular obstruction with pigment casts

§        Siderosis of the kidney


§        Free Hb is scavenged by nitric oxide so also prone to:

§        Abdominal pain +/- diarrhoea and constipation

§        Dysphagia

§        Erectile dysfunction

§        Pulmonary and systemic hypertension



§        Anaemia

§        Blood film not diagnostic - polychromasia

§        If normocytic probably because of concurrent iron deficiency

§        Neutropenia and thrombocytopenia

§        Flow cytometry

§        Red cells (CD59 or 55)

§        Useful to determine the degree of GPI anchor deficiency (looks for a CD59 deficient population.

§        May give false negatives due to the short half life of PNH cells

§        White cells (CD59, CD24, CD16)

§        More sensitive and specific as no problem with short half life.

§        May be difficult to detect in severe aplastic anaemia (neutropenia)

§        FLAER, a modified bacterial protein, which binds GPI anchors and hence doesn’t bind PNH cells.

§        Only works on white cells rather than red cells

§        PIGA gene analysis can be performed but this is not used for diagnosis


Traditional diagnostic tests

§        Ham test

§        Unreliable in transfused patients

§        PNH cells lyse in acid solution whereas normal cells do not

§        False positives

§        CDA type II

§        If rbc already coated with lytic antibody, therefore always do with DCT

§        Sucrose lysis


Divided into

1. Classical PNH

§   Mild to moderate cytopenias

§   Normo / hypercellular bone marrow

§   Raised retics / LDH

§   >60% GPI-AP deficient granulocytes


2. Hypoplastic PNH

§   Bone marrow failure - hypocellular marrow

§   Decreased retics / slightly raised LDH

§   Small PNH granulocyte population (<20%)

§   Mainstay of treatment is allogenic BMT, high dose cyclophosphamide or ATG and cyclosporin



1.      Blood product support


2.      Anticoagulation +/- thrombolysis

§        Consider primary prophylaxis - ? generally treat only secondary thrombosis

§        No studies looking at anti-platelet agents


3.      Folate and iron supplementation


4.      Allogeneic-BMT

§   Mainstay of treatment until the arrival of eculizumab


5.      Gene therapy??

§        Replacement of CD59

§        Eg alternative glycolipid anchor = conceptual


6.      Eculizumab (TRIUMPH trial –NEJM Hillman et al., 2006)

§        Mononclonal Ab to C5 that inhibits the terminal stage of the complement cascade

§        Prevents C5 cleavage to C5a and C5b and thus formation of the membrane attack complex

§        Infusion every 2 weeks

§        Increases risk for neisserial infections due to blockade of complement, therefore vaccinate against Neisseria meningitides and have high level of suspicion (0.5 cases / 100 patient years)

§        Double blind RCT 87 patients

§        50% of patients became independent of transfusion cf 0% in placebo group (median transfused red cells 0 v 10 units)

§        LDH significantly improved

§        Complement control breakthrough

§        Need to maintain levels at > 35ug/ml to maintain complete complement blockade, otherwise you can see an acute attack of IVH just prior to the next dose – can usually be overcome with a dose increase

§        If stopped suddenly, at risk of a sudden severe drop in Hb – PNH cells survive and are at risk of simultaneous break down

§        Hb may not return to normal as red cells still coated with C3 and will undergo extravascular haemolysis

§        Monitor ferritin – at risk of iron overload as they lose their protective haemosiderinuria

§        Effect on thrombotic Blood 2007

§        RR of 85% eculizumab v placebo on thromboembolic events (7 to1 events/ 100 patient years)

§        Similar reduction in anticoagulated patients

§        Increases

§          QOL

§        Renal function



Important Papers

The Complement Inhibitor Eculizumab in Paroxysmal Nocturnal Hemoglobinuria

Hillmen, et al., NEJM 2006