Polymyalgia Rheumatica Following Influenza B Infection: A Case Report

We describe a case of polymyalgia rheumatica (PMR) following an influenza B infection. The patient was a 71-year-old woman who developed a fever above 38.0°C and was diagnosed with influenza B, confirmed by a rapid antigen test. Although the fever resolved after three days, she continued to experience neck pain, back pain, and joint pain, particularly in both shoulders and hips. She also reported morning joint stiffness lasting for more than an hour and occasional low-grade fever. She presented to our hospital 25 days after the onset of symptoms. Blood tests revealed elevated C-reactive protein and erythrocyte sedimentation rate, but levels of creatine phosphokinase, rheumatoid factor, and anti-cyclic citrullinated peptide were not elevated. She was diagnosed with PMR and treated with prednisolone (PSL) 15 mg/day. The response to steroids was remarkably good, and PSL was tapered over six months. PMR is believed to result from an immune-mediated process and may be associated with certain human leukocyte antigen haplotypes. Additionally, PMR is sometimes preceded by an infection. To date, there have been very few reports suggesting a connection between influenza B and PMR, underscoring the need for further case accumulation.