A rare case of symptomatic creatine kinase elevation in a patient with rheumatoid arthritis treated with baricitinib.

The safety profile of baricitinib (BARI), a Janus kinase inhibitor broadly used for the treatment of rheumatoid arthritis (RA), includes asymptomatic laboratory abnormalities, such as an increase in creatine kinase (CK). Data from randomized controlled trials suggest that concomitant myalgia is rare in RA and does not lead to drug discontinuation. We describe the case of a 68-year-old Caucasian female with longstanding, multi-failure RA who started BARI and achieved disease remission. However, she developed a symptomatic CK increase, as well as a parallel increase in total cholesterol, low-density lipoprotein, and triglycerides. Dechallenge-rechallenge demonstrated a plausible relationship between the clinical/laboratory abnormalities and BARI. In fact, when the drug was withdrawn, CK returned to normal and myalgia disappeared, whereas symptoms returned and CK levels increased when BARI was restarted. BARI may be rarely associated with symptomatic CK elevation, and this may pose clinical challenges, particularly for patients with multi-failure RA who achieved good disease control with BARI but required drug discontinuation due to intolerance.