Health care costs before and after diagnosis of depression in patients with unexplained pain: a retrospective cohort study using the United Kingdom General Practice Research Database

Catherine Reed,¹ Jihyung Hong,² Diego Novick,¹ Alan Lenox-Smith,³ Michael Happich<sup>4

1</sup>Global Health Outcomes, Eli Lilly and Company, Windlesham, Surrey, UK; ²Personal Social Services Research Unit, London School of Economics and Political Science, London, UK; ³Eli Lilly UK, Basingstoke, UK; ⁴Eli Lilly and Company, Bad Homburg, Germany

Purpose: To assess the impact of pain severity and time to diagnosis of depression on health care costs for primary care patients with pre-existing unexplained pain symptoms who subsequently received a diagnosis of depression.
Patients and methods: This retrospective cohort study analyzed 4000 adults with unexplained pain (defined as painful physical symptoms [PPS] without any probable organic cause) and a subsequent diagnosis of depression, identified from the UK General Practice Research Database using diagnostic codes. Patients were categorized into four groups based on pain severity (milder or more severe; based on number of pain-relief medications and use of opioids) and time to diagnosis of depression (≤1 year or >1 year from PPS index date). Annual health care costs were calculated (2009 values) and included general practitioner (GP) consultations, secondary care referrals, and prescriptions for pain-relief medications for the 12 months before depression diagnosis and in the subsequent 2 years. Multivariate models of cost included time period as a main independent variable, and adjusted for age, gender, and comorbidities.
Results: Total annual health care costs before and after depression diagnosis for the four patient groups were higher for the groups with more severe pain (£819–£988 versus £565–£628; P < 0.001 for all pairwise comparisons) and highest for the group with more severe pain and longer time to depression diagnosis in the subsequent 2 years (P < 0.05). Total GP costs were highest in the group with more severe pain and longer time to depression diagnosis both before and after depression diagnosis (P < 0.05). In the second year following depression diagnosis, this group also had the highest secondary care referral costs (P < 0.01). The highest drug costs were in the groups with more severe pain (P < 0.001), although costs within each group were similar before and after depression diagnosis.
Conclusion: Among patients with unexplained pain symptoms, significant pain in combination with longer time from pain symptoms to depression diagnosis contribute to higher costs for the UK health care system.

Keywords: depression, pain, cost, GPRD, UK