Paroxysmal nocturnal haemoglobinuria in aplastic anaemia.

The syndrome of paroxysmal nocturnal haemoglobinuria is a stem cell disorder characterized by the production of abnormal cells in all three lines of the peripheral blood. These cells react abnormally with the activated components of complement, resulting in the clinical symptoms. The clone of stem cells characteristic of paroxysmal nocturnal haemoglobinuria may arise spontaneously without demonstrable abnormalities of the other stem cells of the bone marrow. On the other hand, the abnormal stem cells of paroxysmal nocturnal haemoglobinuria may arise as part of a prior stem cell disorder. This is especially true for aplastic anaemia. The paroxysmal nocturnal haemoglobinuria stem cell may arise at any time during the evolution from aplasia through recovery and may disappear during full recovery of the bone marrow. The paroxysmal nocturnal haemoglobinuria stem cell may arise less commonly in other disorders of the stem cell, such as refractory anaemia with excess blasts, erythroleukaemia and myelofibrosis. As with all disorders of the stem cells, paroxysmal nocturnal haemoglobinuria and aplastic anaemia may eventuate into acute leukaemia.