[A case of giant cell arteritis after prednisolone dose reduction during treatment of polymyalgia rheumatica].

Giant cell arteritis (GCA) is closely associated with polymyalgia rheumatica (PMR). We herein report an 82-year-old woman who developed GCA during PMR treatment. She initially presented with shoulder pain and was diagnosed with PMR based on elevated serum C-reactive protein (CRP) levels and bursitis detected in both shoulders on ultrasonography (US). Treatment was initiated with a daily dose of 15 mg prednisolone (PSL), which led to rapid symptom alleviation, and the dosage was tapered to 1 mg/day. One month later, she developed myalgia extending from the lumbar region to the thigh and tenderness in the left temporal region. However, no abnormalities in the temporal artery were observed on US. Although the PSL dose was increased to 2 mg for relapse of PMR, the symptoms did not improve. One week later, she developed occipital pain with an increased CRP level of 9 mg/dL. She was diagnosed with GCA based on the 1990 ACR Classification Criteria. Fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) detected anomalous accumulations in the bilateral superficial temporal and vertebral arteries, but not in the larger vessels. We therefore diagnosed her with cranial-type GCA. At this time point, we repeated US and found a halo sign in the temporal artery. Although epithelioid and giant cells were not observed in the temporal artery biopsy, vascular inflammatory findings such as disruption of the internal elastic lamina and chronic inflammatory cell infiltration were noted. Symptoms improved immediately and CRP levels decreased after the PSL dose was increased to 30 mg daily. To mitigate the risk of steroid-induced diabetes, tocilizumab was introduced, and gradual tapering of PSL was implemented. In conclusion, we encountered a case of GCA that developed after PSL reduction during the course of PMR. PET/CT confirmed intracranial artery inflammation and facilitated a definitive diagnosis. Although PET/CT cannot be routinely performed for diagnose in Japan, we consider it useful as an adjunctive diagnostic tool.