We describe the first case of an elderly patient who experienced exacerbation of a previously undiagnosed sporadic inclusion body myositis (sIBM), the most common myopathy in the geriatric population, which was triggered by anti-programmed cell death-1 therapy.<h4>Case presentation</h4>A 75-year-old man who was receiving pembrolizumab presented with limb weakness. Here, PDCD1 is linked to inclusion body myositis.