Paroxysmal Nocturnal Hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hemolytic disease of insidious onset and chronic course, characterized by an intracorpuscular erythrocytic defect rendering the cells unusually susceptible to hemolysis in vitro and probably in vivo upon slight acidification of the plasma. The constant feature of the disease is hemosiderinuria, rather than hemoglobinuria¹; in some cases hemoglobinuria may occur rarely or not at all.²⁻⁵Although an excellent account of this syndrome was provided by Striibing, in 1882,⁶only 38 cases had been recorded by 1937.⁷Crosby's classic monograph in 1953 analyzed the clinical and laboratory features of 162 collected cases.⁸Since then, many typical cases have been readily recognized by their clinical features, with subsequent laboratory confirmation by the Ham acid-hemolysis test,⁹and 18 additional cases have been reported.¹⁰,²³ The atypical clinical and serologic features of the following three cases rendered diagnosis difficult and merit mention. Two of these cases presented with