Adult-onset Still's disease presenting with aseptic meningitis as the first symptom in an elderly patient

•Neutrophilic meningitis is rarely observed in Adult onset Still's disease (AOSD).•AOSD-related meningitis has been observed in the AOSD course of young adults.•An elderly man showed neutrophilic meningitis as a first symptom of AOSD.•First-line therapy with steroid for bacterial meningitis complicated the diagnosis.•Hyperferritinemia led to the correct diagnosis of AOSD and AOSD-related meningitis.