[Therapy-refractory thrombocytopenia in a 28-year-old patient].

We report a case of a patient with thrombocytopenia. A sporadic MYH9-associated disease, May Hegglin anomaly, was identified by giant platelets, leucocyte inclusion bodies and the typical distribution of NMMHC-IIA in granulocytes in the absence of impaired renal function, cataract and hearing loss. MYH9-associated diseases are an underestimated differential diagnosis of idiopathic thrombocytopenia. The correct diagnosis is important to prevent unnecessary treatment of a patient with thrombocytopenia and to provide sufficient patient information and genetic counseling. Therefore, careful examination of the blood smear has to be the first diagnostic step in a case of unexplained thrombocytopenia.