Platelet‐associated IgG for the diagnosis of immune thrombocytopaenic purpura during peginterferon α and ribavirin treatment for chronic hepatitis C

To the Editor: Mild-to-moderate thrombocytopaenia is a common adverse event of treatment with conventional or pegylated interferon a, attributed primarily to bone marrow suppression, in patients with chronic hepatitis C. Nevertheless, severe, life-threatening immune thrombocytopaenic purpura (ITP) has rarely been associated with interferon treatment (1–7). The pathogenesis of ITP is incompletely understood, but immunoglobulin G (IgG)-type antibodies against platelet membrane glycoproteins (IIb/IIIa, Ib/IX, etc.) are involved (8). We describe a case of ITP induced by peginterferon treatment for chronic hepatitis C. Detection of platelet-associated IgG was helpful for the diagnosis. A 69-year-old woman with chronic hepatitis C genotype 1b infection started to receive peginterferon a2b 80 mg/week and ribavirin 600 mg/day in October 2006 (Fig. 1). At the start of therapy, she was well, with a height of 155 cm and a weight of 58 kg. The laboratory values were as follows: aspartate aminotransferase 44 IU/L, alanine aminotransferase 58 IU/L, g-glutamyltransferase 32 IU/L, bilirubin 0.9 mg/dl, albumin 4.1 g/dl, hepatitis C virus (HCV) RNA 43 kIU/ml, haemoglobin concentration 14.4 g/dl, white blood cell count 5400/mm and platelet count 139 000/mm. A liver biopsy specimen showed moderate inflammation and mild fibrosis. After the start of therapy, the serum HCV RNA level rapidly decreased and became negative on polymerase chain reaction at the fourth week. The platelet count gradually declined to 86 000/ mm by the 13th week of therapy and then rapidly declined to 14 000/mm at the 16th week. She had petechiae on the upper extremities. Peginterferon and ribavirin were withdrawn. Coagulation test results were normal. A direct Coombs’ test result was negative. Antinuclear and anticardiolipin antibodies were negative. Cryoglobulins were not detected. Serum was negative for antiplatelet antibody by mixed passive haemagglutination. However, the platelet-associated IgG level on the platelet surface had increased to 372 (reference range, 9.0–25.0) ng/10 cells as measured by an enzyme-linked immunoassay. Bone marrow