Prevalence and characteristics of postoperative and nonoperative chronic hypoparathyroidism in Japan: a nationwide retrospective analysis.

Hypoparathyroidism is a rare endocrine disorder characterized by low serum calcium and elevated serum phosphorus levels. Patients who do not recover parathyroid function after surgeries or have nonsurgical causes involving congenital and metabolic diseases, require long-term use of active vitamin D and calcium supplementation as conventional therapy in Japan. This study aimed to estimate prevalence of chronic hypoparathyroidism and investigate its disease etiology, patient characteristics, and treatment in Japan, using a health insurance claim database. Individuals who were available in the 4-yr observation period spanning 2015-2018 (2015-2017 for look-back and 2018 for prevalence estimation) were eligible for the denominator. Chronic hypoparathyroidism was defined as individuals who had both a record of prescription of conventional therapy for hypoparathyroidism in 2018 and a record of relevant surgery, radiotherapy, or disease at least 6 mo apart. Among the denominator ( = 2 241 717), 509 patients with chronic hypoparathyroidism were identified (mean age of 49 yr). The standardized prevalence of chronic hypoparathyroidism in 2018 was 38.3 (95% CI: 33.4-43.6) per 100 000 individuals, with 37.0 (32.2-42.3) and 1.2 (0.8-2.0) per 100 000 for postoperative and nonoperative causes, respectively. Six percent of the patients had chronic kidney disease as a comorbidity. Chronic hypoparathyroidism had heterogenous causes, with thyroid malignancy and 22q11.2 deletion syndrome being the most common postoperative and nonoperative causes, respectively. The mean duration of prescribed vitamin D and calcium was 963 and 629 d, respectively, during the 4-yr period. The prevalence of chronic hypoparathyroidism was similar but slightly higher than estimates reported for the United States and Europe, which may be due to the differences in study designs and high healthcare accessibility in Japan. Our study suggests that there is a nonnegligible number of patients, ~48 500 patients, with chronic hypoparathyroidism in Japan.