Abrupt fluctuation from extreme hyperleukocytosis to severe myelosuppression by nilotinib in a case of chronic myeloid leukemia

Abstract: Hyperleukocytosis can be seen in newly diagnosed chronic myeloid leukemia (CML), but levels exceeding 500 × 10 9 /L are rare. During medication-induced reduction of high leukocyte levels, blood cell counts typically decrease gradually to normal levels rather than causing abrupt severe myelosuppression. We present a remarkable case of a 28-year-old male diagnosed with chronic phase CML who exhibited two extreme and contrasting clinical manifestations during his disease course. At initial presentation, the patient demonstrated severe hyperleukocytosis with an extraordinarily elevated white blood cell count of 751.87 × 10 9 /L, accompanied by clinically significant leukostasis symptoms requiring urgent intervention. Following initiation of nilotinib therapy, the clinical course took an unexpected turn as the patient developed abrupt and severe grade 4 myelosuppression, representing a dramatic hematologic shift. The simultaneous occurrence of these two opposing clinical extremes – extreme leukocytosis followed by profound cytopenia in the same patient constitutes an exceptionally rare phenomenon in CML management. This case highlights the unpredictable nature of treatment responses in CML and underscores the need for vigilant monitoring even in chronic phase patients.