Elevated White Blood Cell Count and Lactate Dehydrogenase Levels Are Important Markers for Diagnosing Relapse of Adult-onset Still's Disease under Tocilizumab Use.

We encountered a case of refractory adult-onset Still's disease (AOSD) with two relapses. Prednisolone and methotrexate were begun as induction therapy, resulting in the patient's first relapse during tapering of prednisolone. After the introduction of tocilizumab, she achieved remission. However, she experienced a second relapse following prednisolone tapering. While lactate dehydrogenase (LDH) levels and white blood cell (WBC) counts increased in both relapses, interleukin-6 (IL-6) suppression resulted in stable C-reactive protein and ferritin levels in the second relapse. A comparison of the two relapses indicated that increases in both WBC counts and LDH levels can aid in the diagnosis of AOSD relapse.