Psychiatric, Neurological, and Somatic Comorbidities in Intermittent Explosive Disorder.

Importance: Intermittent explosive disorder (IED) is an understudied psychiatric condition marked by impulsive aggression and poorly regulated emotional control, often resulting in interpersonal and societal consequences. Better understanding of comorbidities can improve screening, diagnosis, and treatment. Objective: To investigate the prevalence of IED and its associations with psychiatric, neurological, and somatic disorders. Design, Setting, and Participants: In this cohort study, matched groups of patients with and without IED were identified from the TriNetX Research Network (dated January 31, 2024). Electronic medical record data were analyzed. The mean (SD) time from the first to last known visits was 4.8 (5.4) years. Exposure: Lifetime diagnosis of IED. Main Outcomes and Measures: Main outcomes were International Statistical Classification of Diseases, Tenth Revision, Clinical Modification diagnostic categories and root codes. Cox proportional hazard models were used to estimate and compare probabilities of acquiring other diagnoses. Key measures include the numbers and proportions of patients with these diagnoses and adjusted hazard ratios (HRs) for IED. Results: Overall, 30 357 individuals with IED and 30 357 demographically matched controls were included. In each group, 21 313 (70%) were male, with a mean (SD) age at the first visit 26 (17) years. Despite only 0.03% of the total patient population having an IED diagnosis, extensive comorbidities with psychiatric, neurological, and somatic conditions were found. A notable 95.7% of individuals with IED (29 054 individuals) had another psychiatric diagnosis. All psychiatric subcategories and 92% of the psychiatric diagnoses were significantly associated with IED, with HRs ranging from 2.1 (95% CI, 2.0-2.2) for substance use disorder to 76.6 (95% CI, 65.4-89.6) for disorders of adult personality and behavior (excluding IED). Among neurological conditions, neurodegenerative diseases (HR, 5.0; 95% CI, 4.1-6.1) and epilepsy (HR, 4.9; 95% CI, 4.3-5.6) had the highest HRs, followed by movement disorders (HR, 3.1; 95% CI, 2.8-3.5), cerebral palsy (HR, 2.6; 95% CI, 2.2-3.0), and sleep disorders (HR, 2.2; 95% CI, 2.1-2.3). Significant associations with IED were also observed for many somatic diseases, including obesity (HR, 1.6; 95% CI, 1.5-1.7), hyperlipidemia (HR, 1.5; 95% CI, 1.4-1.5), hypertension (HR, 1.6; 95% CI, 1.5-1.7), and gastroesophageal reflux disease (HR, 1.7; 95% CI, 1.7-1.9). Conclusion and Relevance: These findings highlight the extensive comorbidities between IED and psychiatric, neurological, and somatic disorders, emphasizing the need for integrated diagnostic and treatment approaches addressing both psychological and physical health aspects of IED. Limitations related to reliance on medical records and low diagnostic rates of IED caution the generalizability of these findings, underscoring the need for further validation in prospective studies and more accurate, inclusive diagnosis of IED in patients with mental disorders.