“Polyarthritis associated with myositis-like features following relugolix initiation in a patient with prostate cancer: a case report”

Relugolix is a recently approved oral gonadotropin-releasing hormone (GnRH) antagonist (2021), indicated for the treatment of prostate cancer. While musculoskeletal adverse effects are frequently reported, data on severe manifestations remain rare. We describe the case of a patient who developed polyarthritis associated with myositis-like features accompanied by marked systemic inflammation and fever, following the initiation of relugolix treatment. Discontinuation of the drug combined with a short course of corticosteroids resulted in complete remission, with no relapse after six months of corticosteroid-free follow-up. This case suggests a potential association between relugolix and severe inflammatory musculoskeletal manifestations, including polyarthritis with myositis-like features. Although causality cannot be definitively established, the temporal relationship, improvement after relugolix withdrawal, and absence of recurrence with subsequent androgen deprivation support the possibility of a drug-specific effect. Clinicians should be aware of these potentially severe but poorly documented adverse events.