Comments on: "a case of isoniazid-induced thrombocytopenia: recovery with immunoglobulin therapy".

To the Editor I read with great interest the article " A case of isoniazid-induced thrombocytopenia: recovery with im-munoglobulin therapy " in volume 51, number 7, April 2012 issue of your journal (1). As the authors mentioned, this case represents a rare adverse event associated with isoni-azid therapy, namely, isoniazid-induced thrombocytopenia. It is well known that almost all anti-tuberculosis drugs may cause thrombocytopenia, but isoniazid-induced thrombocy-topenia is a very rare entity, and the mechanism of action underlying this adverse effect is unclear. In the present case, the authors reported anemia (hemoglobin level, 8.3 g/dL; and hematocrit, 25%) and abnormal liver functions (aspar-tate aminotransferase/alanine aminotransferase level, 585/688 U/L; and total bilirubin level, 2.46 mg/dL), besides the thrombocytopenia. These findings suggest the presence of hemolytic anemia with a low level of hemoglobin, and elevated serum transaminase and bilirubin levels. It was also noted that there was nasal bleeding after admission, but this was not considered to be a major bleeding episode severe enough to cause anemia. In contrast, the present case had thrombocytopenia and hemolytic anemia most probably caused by isoniazid due to an immunological reaction. Therefore, I would like to suggest that the authors perform a direct anti-globulin test to highlight the underlying immunological reaction (if present) and to thus make a differential diagnosis. It is well known that Evans Syndrome is a condition defined by a combination of thrombocytopenia and autoimmune hemolytic anemia , with a positive direct anti-globulin test in the absence of known underlying etiology (2). If the authors had performed an anti-globulin test, the etiology of the isoniazid-induced thrombocytopenia and anemia could be more conclusively defined, and might also make a valuable contribution to further defining cases diagnosed with drug-induced thrombocytopenia and Evans Syndrome.