Acute leukemia presenting with blasts first found in the cerebrospinal fluid but not in the peripheral blood

Acute leukemia presenting with central nervous system (CNS) signs and symptoms is uncommon and prone to be misdiagnosed. Here, we report nine patients with acute leukemia, including five patients with acute lymphoblastic leukemia (ALL) and four patients with acute myeloid leukemia (AML). These patients presented with symptoms suggestive of involvement of multiple cranial nerves, the spinal cord, and meningeal involvement. Moreover, we found that all these patients unexpectedly showed the presence of blasts in the cerebrospinal fluid (CSF) but not in the peripheral blood despite repeated examinations. Bone marrow examination confirmed the presence of acute leukemia in these patients. Seven patients died within 18 months of diagnosis and two patients developed stable disease. Our findings show a novel presenting feature of acute leukemia and highlight the importance of CSF cytology in the diagnosis of acute leukemia.