Type 2 diabetes mellitus complicated with idiopathic hypoparathyroidism where poor glycaemic control was associated with low adherence to exercise and medication due to hypocalcaemia.

We report a rare case of type 2 diabetes mellitus (T2DM) complicated with idiopathic hypoparathyroidism. A 36-year-old Japanese man was admitted to our hospital owing to poor glycaemic control and hypocalcaemia. The patient had myalgia resulting from hypocalcaemia, which prevented adequate exercise. He considered the onset of myalgia to be an adverse event of oral hypoglycaemic agents and reduced compliance to medication; however, his serum calcium level was never measured. Treatment for hypocalcaemia immediately improved the myalgia, facilitating regular exercise therapy and ensuring compliance with prescribed medications, as the now-resolved myalgia was no longer perceived to be an adverse effect of glucose-lowering agents; this improved glycaemic control. Although hypoparathyroidism is a rare disease, it is necessary to assess serum calcium levels in patients with T2DM, particularly in cases presenting with unidentified complaints such as myalgia.