Outcome and follow-up
Prior to the autoimmune serology results becoming available, a clinical diagnosis of PMR was made. This was based on the elevated inflammatory markers, typical joint involvement and symptoms, and patient demographic. The differential diagnoses included other autoimmune arthritis such as RA or seronegative spondyloarthropathy. The inflammatory arthritis was thought to be secondary to denosumab given the time course of symptom onset soon after the injection.
Early in the admission, the patient was started on celecoxib with minimal improvement. Given the suspicion for PMR, he was subsequently started on 10 mg prednisolone once daily. There was a remarkably good response the following day, with the patient returning to full range of motion in his right shoulder as well as noting significant reduction in musculoskeletal pain.
The uptrending CRP began to decrease after starting prednisolone–the level was 235.2 mg/L the day prior to initiating therapy, and declined to 178.9 mg/L one day after the initial 10 mg dose. He was discharged after two days with a slow weaning dose of prednisolone and planned for rheumatology clinic follow-up. The patient was advised to switch to a different osteoporosis treatment.
The subsequently available results of an elevated RF and ACPA led to the revised diagnosis of denosumab-induced seropositive inflammatory arthritis with overlapping features of late-onset RA and PMR.