Purpose: We present a case of a patient with optic neuritis who had underlying suspicious idiopathic thrombocytopenic purpura.
Case summary: A 35-year-old female with no other systemic disease visited our clinic due to acutely decreased visual acuity in her left eye 10 days in duration. Relative afferent pupillary defect was observed, but without definite papilledema. Based on brain magnetic resonance imaging (MRI), optic neuritis was suspected. Laboratory tests showed increased red blood cells, hemoglobin and, hematocrit levels and decreased platelets. Peripheral blood smear test showed decreased platelets, relative lymphocytosis and atypical lymphocytes. Specific antibodies for autoimmune disease were not present. High-dose steroid pulse therapy (methyl prednisolone 1.0 g/d, 3 days) was started. One month after treatment her visual acuity and platelet count recovered and her visual field defect improved.