A Burden and Prevalence Analysis of Chronic Pain by Distinct Case Definitions among Active Duty U.S. Military Service Members, 2018

Background: Chronic pain is a growing problem in the military, and the methods by which we have to perform epidemiologic surveillance are insufficient. It represents both a public health and military readiness concern, as those who suffer from it experience adverse impacts on work productivity, physiological health, and quality of life. Objectives: This study was designed to assess the prevalence of chronic pain among active component military service members utilizing 2 distinct, published case definitions. It sought to describe the demographics and military characteristics of those receiving chronic pain diagnoses. The study also aimed to provide improved granularity regarding military chronic pain patients’ pain severity and its impacts on their job performance. Study Design: Cross-sectional analysis for 2018. Setting: This analysis utilized data available from the Defense Medical Surveillance System, a database containing longitudinal data on service members. Methods: Patients: The surveillance population consisted of all active component service members from the U.S. Army, Navy, Air Force, and Marines of all grades serving at any point during the surveillance period of January 1, 2018 through December 31, 2018. Measurement: Diagnoses were ascertained from the administrative records of all medical encounters of individuals who received care through the Military Health System or civilian referrals. Data from patients’ Periodic Health Assessment (PHA) encounters were also utilized to derive more granular data regarding their experiences of pain. Results: Case Definition 1, more specific for identifying chronic pain, identified a more severe subset of chronic pain patients when compared against Case Definition 2, a more comprehensive method for identifying potential chronic pain patients. Case Definition 1 found a higher prevalence of impactful pain (CD1: 36.7% vs. CD2: 23.5%), and Case Definition 1 patients are more likely to be on limited duty and require treatment related to their pain. Several demographic groups were also found to be at increased risk of chronic pain diagnosis, including women, black non-Hispanic, Army, older age, and enlisted. Limitations: First, in utilizing administrative data, this allows for the possibility of misclassification bias. Second, some deployment data still used ICD-9 coding even in 2018, resulting in a minor underestimation by approximately 30 patients and approximately 60 encounters. Third, the prevalence estimates for the demographics were not adjusted for potential confounders. Conclusions: Chronic pain has been difficult to define via administrative and screening data, and as such its burden and prevalence estimates can vary considerably depending on which case definition is used. This is of particular importance in the U.S. military, as these estimates can significantly impact our calculations for force readiness and the protection of our national security. To our knowledge, this study is the first of its kind to examine chronic pain across the entirety of the U.S. armed forces and to utilize granular, annually collected PHA data in this way. The results of this exploratory analysis could be used as a template to better characterize the burden of chronic pain from a populationbased perspective and monitor the effectiveness of pain management strategies. Key words: Chronic pain, military, case definition, surveillance, epidemiology