The patient was a 76-year-old woman who had been diagnosed with diabetes when she was 75 years of age. Her blood glucose was initially well controlled by oral antidiabetic therapy. However, she was admitted to our hospital at approximately 6 months after her diagnosis because her casual blood glucose and HbAlc suddenly increased to 675 mg/dL and 11.9 %, respectively, and she also developed ketosis. An investigation to determine the cause of her blood glucose deterioration revealed pancreatic cancer. However, her anti-GAD antibody titer was also extremely high (124,000 U/mL), and she was diagnosed as simultaneously having slowly progressive insulin-dependent diabetes mellitus (SPIDDM). The development of SPIDDM in elderly patients is rare and there have only been a few reports about SPIDDM being diagnosed concurrently with pancreatic cancer. HLA genes were detected in the present patient. These genes are potentially related to disease resistance. It is possible that disease resistance HLA led to the simultaneous development of SPIDDM and pancreatic cancer in this elderly patient. Although pancreatic cancer and SPIDDM rarely occur simultaneously in elderly patients, the possible combination of a malignant tumor and type 1 diabetes mellitus (such as SPIDDM) should be considered if a patient's blood glucose control suddenly deteriorates during diabetes treatment.
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