Abstract
Autism and borderline personality disorder (BPD) are each associated with increased psychiatric emergency department (PsyED) use, yet the service impact of coexisting autism-BPD remains unclear. We conducted a retrospective chart review of 1027 PsyED visits by 345 autistic adults (2018-2020) at an urban Canadian psychiatric hospital to compare service patterns between those with and without a BPD diagnosis. Sociodemographics, presenting reasons, restraint use, and disposition were analyzed using mixed-effects logistic regression. BPD was documented in 33.5% of visits and in 11.0% of unique autistic individuals, more often in birth-assigned females. Among all autistic individuals' PsyED visits, an autism diagnosis was documented in 60.2% of their text-based charts. Furthermore, autism was documented less frequently when BPD was recorded, suggesting possible diagnostic overshadowing. Suicidality as the primary reason for visit was associated with documented BPD (OR 4.366, 95% CI 2.659-7.169; p < 0.001). No significant differences were observed in disposition (discharge vs. admission) or restraint use between birth-assigned sex, BPD status, or documentation of autism within the visit. Findings underscore the need for sex-sensitive, autism-aware assessments and trauma-informed care in PsyED settings, and caution against diagnostic overshadowing that influences clinical decision-making. Limitations include a single-site sample and lack of autism diagnosis timing data, precluding temporal inferences. Future work should test targeted interventions and clarify mechanisms of suicidality among autistic individuals with coexisting BPD. Integrated autism-BPD care pathways, with specialized outpatient supports, sensory-friendly adaptations, and structured referrals, may improve care and reduce PsyED visits.