Hazard of substance abuse onset among adults diagnosed with epilepsy or migraine.

OBJECTIVE: We investigated adult-onset epilepsy as a risk factor for the development of substance use disorder (SUD) by comparing the rate of SUD diagnosis among adults diagnosed with epilepsy with presumably healthy controls with lower extremity fractures (LEF). For additional comparison, we investigated the risk for adults with migraine only. Epilepsy and migraine are both episodic neurological disorders and migraine is frequently comorbid with epilepsy. METHODS: We conducted a time-to-event analysis using a subset of surveillance data of hospital admissions, emergency department visits, and outpatient visits in South Carolina, USA from January 1, 2000, through December 31, 2011. Individuals aged 18 years or older were identified using the International Classification of Disease, 9thRevision Clinical Modification (ICD-9) with a diagnosis of epilepsy (n = 78,547; 52.7% female, mean age 51.3 years), migraine (n = 121,155; 81.5% female, mean age 40.0 years), or LEF (n = 73,911; 55.4% female, mean age 48.7 years). Individuals with SUD diagnosis following epilepsy, migraine, or LEF were identified with ICD-9 codes. We used Cox proportional hazards regression to model the time to SUD diagnosis comparing adults diagnosed with epilepsy, migraine, and LEF, adjusting for insurance payer, age, sex, race/ethnicity, and prior mental health comorbidities. RESULTS: Compared to LEF controls, adults with epilepsy were diagnosed with SUD at 2.5 times the rate [HR 2.48 (2.37, 2.60)] and adults with migraine only were diagnosed with SUD at 1.12 times the rate [HR 1.12 (1.06, 1.18)]. We found an interaction between disease diagnosis and insurance payer, with hazard ratios comparing epilepsy to LEF of 4.59, 3.48, 1.97, and 1.44 within the commercial payer, uninsured, Medicaid, and Medicare strata, respectively. SIGNIFICANCE: Compared to presumably healthy controls, adults with epilepsy had a substantially higher hazard of SUD, while adults with migraine only showed a small, but significant, increased hazard of SUD.