The economic impact of comorbidity in multiple sclerosis.

BACKGROUND: Comorbid conditions are common in people with multiple sclerosis (pwMS). They can delay diagnosis and negatively impact the disease course, progression of disability, therapeutic management, and adherence to treatment. OBJECTIVE: To quantify the economic impact of comorbidity in multiple sclerosis (MS), based on cost-of-illness estimates made using a bottom-up approach. METHODS: A retrospective study was carried out in two northern Italian areas. The socio-demographic and clinical information, including comorbidities data, were collected through ad hoc anonymous self-assessment questionnaire while disease costs (direct and indirect costs of disease and loss of productivity) were estimated using a bottom-up approach. Costs were compared between pwMS with and without comorbidity. Adjusted incremental costs associated with comorbidity were reported using generalized linear models with log-link and gamma distributions or two-part models. RESULTS: 51.0% of pwMS had at least one comorbid condition. Hypertension (21.0%), depression (15.7%), and anxiety (11.7%) were the most prevalent. PwMS with comorbidity were more likely to use healthcare resources, such as hospitalizations (OR = 1.21, p < 0.001), tests (OR = 1.59, p < 0.001), and symptomatic drugs and supplements (OR = 1.89, p = 0.012), and to incur non-healthcare costs related to investment (OR = 1.32, p < 0.001), transportation (OR = 1.33, p < 0.001), services (OR = 1.33, p < 0.001), and informal care (OR = 1.43, p = 0.16). Finally, they experienced greater productivity losses (OR = 1.34, p < 0.001) than pwMS without comorbidity. The adjusted incremental annual cost per patient due to comorbidity was €3,106.9 (13% of the overall costs) with MS disability found to exponentially affect annual costs. CONCLUSION: Comorbidity has health, social, and economic consequences for pwMS.