Adenomyosis symptoms are disabling. Population-based data on incidence and prevalence of adenomyosis are lacking that could guide future evidence-based treatments and clinical management.

To evaluate the incidence, 10-year secular trends, and prevalence of adenomyosis diagnoses and to describe symptoms and treatment patterns in a large U.S. cohort.

We performed a retrospective population-based cohort study of women aged 16–60 years in 2006–2015, enrolled in Kaiser Permanente Washington, a mixed-model health insurance and care delivery system. Adenomyosis diagnoses identified by ICD codes from the International Classification of Diseases 9th and 10th editions and potential covariates were extracted from computerized databases. Women with prior hysterectomy, and for incidence estimates women with prior adenomyosis diagnoses, were excluded. Linear trends in incidence rates over the 10-year study period were evaluated using Poisson regression. Rates and trend tests were examined for all women adjusting for age using direct standardization to the 2015 study population, by age groups, and by race/ethnicity. Chart reviews were performed to validate diagnostic accuracy of ICD codes in identifying adenomyosis incidence. Symptoms and treatment patterns at diagnosis and in the following 5 years were assessed.

A total of 333,693 women contributed 1,185,855 woman-years (2006–2015) for incidence calculations. Associated symptom-related codes (menorrhagia or abnormal uterine bleeding, dysmenorrhea or pelvic pain, dyspareunia, and infertility) were observed in 90.8%; 18.0% had co-occurrent endometriosis codes and 47.6% had co-occurrent uterine fibroid codes. The overall adenomyosis incidence was 1.03% or 28.9 per 10,000 woman-years, with a high of 30.6 in 2007 and a low of 24.4 in 2014. Overall age-adjusted estimated incidence rates declined during the 10-year study interval (linear trend P < .05). Incidence was highest for women aged 41–45 years (69.1 per 10,000 woman-years in 2008) and was higher for black (highest 44.6 per 10,000 woman-years in 2011) vs white women (highest 27.9 per 10,000 woman-years in 2010). Overall prevalence in 2015 was 0.8% and was highest among women aged 41–45 years (1.5%). Among the 624 potential adenomyosis cases identified by diagnostic codes in 2012–2015 and with sufficient information in the medical record to determine true case status, 490 were confirmed as incident cases, yielding a 78.5% (95% confidence interval, 75.1%, 81.7%) positive predictive value of adenomyosis ICD-9/ICD-10 codes for identifying an incident adenomyosis case. Health care burden was substantial: 82.0% of women had hysterectomies, nearly 70% had imaging studies suggestive of adenomyosis, and 37.6% used chronic pain medications.

Adenomyosis burden to the individual and the health care system is high. Incidence rates are disproportionately high among black women. These findings are of concern, as currently available long-term medical therapies remain limited beyond hysterectomy. Our data and methodologies are novel and could serve as a foundation to guide clinicians and health care systems to develop clinical management plans and track outcomes for women with adenomyosis.