Introduction
Denosumab is a fully human monoclonal antibody against the receptor
activator of nuclear factor kappa B ligand (RANKL), commonly used to
treat osteoporosis in males and postmenopausal
females.1 Rare but serious adverse effects include
hypersensitivity reactions, atypical femoral fractures, severe
infections and hypocalcaemia.1,2 Relatively common
side effects include mild infections, arthralgia and musculoskeletal
pain–with a reported incidence of 7.7% in the FREEDOM
trial.2,3
Denosumab-induced arthralgia and musculoskeletal pain is typically
transient and mild, and not associated with an acute phase
response.4 In contrast, an acute phase response
manifesting as a flu-like syndrome is a relatively common adverse effect
of bisphosphonates.5 In a Phase III denosumab
study,6 2% of patients had a flare of underlying
polymyalgia rheumatica (PMR)–an inflammatory disorder typically
presenting with shoulder and pelvic girdle musculoskeletal
pain.7 However, there are no previous reports of
new-onset PMR or other inflammatory arthritis following denosumab use.
Furthermore, denosumab has also been studied in patients with rheumatoid
arthritis (RA)–a systemic autoimmune disease characterised by synovitis
and localised joint destruction–with no reports of flares secondary to
denosumab.8-10
We present a case of an elderly patient who developed a flare of
previously undiagnosed seropositive inflammatory arthritis with
overlapping features of PMR and RA, after treatment with denosumab.