Multimorbidity and Sickness Absence/Disability Pension in Cluster Headache Patients and Matched References: A Swedish Register-Based Study

Multimorbidity among cluster headache (CH) patients is considered to be high, but large studies are lacking. The aims were to explore the occurrence of diagnosis-specific multimorbidity among CH patients and matched references and possible associations of this with their sickness absence and disability pension.We performed a register-based study of CH patients and matched references, regarding their multimorbidity, sickness absence and disability pension. Data was obtained from two nationwide registers: Statistics Sweden's Longitudinal Integration Database for Health Insurance and Labor Market Studies (LISA) (for sociodemographics in 2009, sickness absence and disability pension in 2010) and The National Board of Health and Welfare's specialized out-patient and in-patient registers for diagnosis-specific healthcare in 2001-2010 (for identifying CH patients and multimorbidity, defined by ICD-10 codes). The prevalence and number of net days of sickness absence and/or disability pension in 2010 was calculated; in general, and by multimorbidity. Odds ratios (OR) with 95% confidence intervals (CI) were calculated for comparison of each diagnostic group with references without the chosen morbidity.We analysed 3,240 CH patients, aged 16-64 years, and living in Sweden in 2010, and 16,200 matched references. A higher proportion of CH patients had multimorbidity (91.9%) than of references (77.6%); OR 3.263 (95% CI 2.861-3.721), both in general and regarding all analysed diagnostic groups. Differences were particularly high for diagnoses relating to the nervous (CH 51.8% vs. references 15.4%); OR 5.922 (95% CI 5.461-6.422), and musculoskeletal (CH 39.0% vs. references 23.7%); OR 2.057 (95% CI 1.900-2.227) systems. Multimorbidity rates were overall higher among women in CH patients (96.4% vs. men 89.6%). CH patients had higher mean number of days of sickness absence and disability pension compared to references, 63.15 vs. 34.08 days. Moreover, multimorbidity was associated with higher mean number of such days in CH patients, 67.25, as compared to references, 40.69 days.The proportions of multimorbidity were high in both CH patients and references, however, higher in the CH patients, who also had higher sickness absence and disability pension levels. Especially, CH patients with multimorbidity and of female sex had high sickness absence and disability pension levels.