(PS14-89) Does Fear of Sleep Mediate the Relation Between Service Dog Partnership and PTSD Severity?

Introduction: An estimated 29% of post-9/11 veterans are diagnosed with PTSD, a condition that is associated with many sleep-related challenges. One notable challenge is fear of sleep, for example due to distressing nightmares. Moreover, hyperarousal and hypervigilance, hallmark symptoms of PTSD, can exacerbate feelings of vulnerability during sleep. Psychiatric service dogs may be promising as a complimentary intervention for veterans to supplement first-line care for PTSD. This presentation will report findings from an exploratory analysis of data from an NIH-funded (R21HD091896) non-randomized clinical trial in which veterans with PTSD were assessed after psychiatric service dog placement or while on the waitlist. Our objective was to investigate whether fear of sleep mediates the relation between service dog placement and PTSD symptom severity.

Methods: Participants (N = 168; n = 91 in the service dog group and n = 77 waitlisted controls) completed the PTSD Checklist for DSM-5 (PCL-5) and Fear of Sleep Inventory (FOSI) at baseline (i.e. prior to service dog placement) and 3-month follow-up. A mediation analysis was performed. Linear regression was used to fit the mediator model for the conditional distribution of FOSI scores at follow-up, group and covariates: baseline FOSI and PCL-5, gender, and age. The conditional distribution of PCL-5 scores at follow-up given the treatment group, follow-up FOSI scores, gender, and age was fit with linear regression. Finally, we assessed a possible treatment-mediator interaction between service dog and FOSI.

Results: The estimated total effect of service dog placement on PTSD severity was -11.2 (95% CI: [-16.0, -6.4]). The estimated effect of service dog placement on PCL-5 scores mediated by FOSI scores was -2.6 (95% CI: [-5.1, -0.7]). The estimated proportion of the effect of service dog placement on PCL-5 scores mediated by FOSI scores was 0.23 (95% CI: [0.07, 0.56]). There was no evidence of a treatment-mediator interaction between service dogs and FOSI scores (p = 0.15).

Conclusion: The exploratory analysis revealed that fear of sleep mediated the relation between service dog partnership and PTSD severity, accounting for 20% of the reduction in PTSD symptoms. This pathway could be attributed to various factors. Veterans might perceive a sense of security knowing that their service dog might alert them if needed, allowing them to “let down their guard” when sleeping. Furthermore, the presence of a service dog may offer reassurance about nightmares, as they can interrupt or provide comfort if one occurs. However, it's noteworthy that fear of sleep only partially explained the severity of PTSD symptoms. Other potential mechanisms, such as the dog's trained tasks, its mere presence, and its impact on stress hormone levels, could also play a role in mediating PTSD symptoms.

Support: (clinicaltrials.gov ID: NCT03245814)