BACKGROUND The differential diagnosis of generalized pain includes reactivity associated with bacterial and viral infections, autoimmune rheumatic disease, and orthopedic diseases. Obtaining a detailed medical history and establishing an accurate diagnosis are difficult in elderly patients with dementia. In addition, the differential diagnosis between polymyalgia rheumatica and pseudogout is often difficult. Thus, in our work, we examined the importance of interviewing the family of an elderly patient with dementia. CASE REPORT We report the case of an 88-year-old woman with dementia and a history of recurrent pseudogout who presented with a 12-day history of fever and generalized pain. Physical examination findings revealed warmth and swelling in the shoulder joints and right knee. Blood tests indicated increased inflammatory marker levels. The primary working impression was oligo-articular pseudogout. Based on family interview, the patient was seen to manifest atypical symptoms, including movement difficulty. Joint ultrasound findings showed inflammation of the left long head of the biceps attachment. Further, right knee arthrocentesis detected no calcium pyrophosphate crystals. After obtaining a detailed medical history from the patient's family and conducting other diagnostic tests, the patient was finally diagnosed with polymyalgia rheumatica, rather than oligo-articular pseudogout, with rapid improvement after undergoing low-dose prednisolone treatment. CONCLUSIONS Family interviews can be helpful for obtaining correct diagnosis in elderly patients with dementia.