Multiple sclerosis (MS) is an autoimmune disease affecting principally the central nervous system, causing nerve sheath lesions, axon damage, and paralysis. MS symptoms include muscle weakness, weak reflexes, tremors, muscle spasms, prolonged double vision, slurred speech, and balance problems. MS can occur at any age, but commonly affects people of ages 15–60 years. MS is a progressive disease for which there is no cure. Major depressive disorder (MDD) is strongly associated with MS and patients with MS are more likely to have more severe depression compared to the general population.

According to a January 2023 study conducted by Siddiqi and colleagues and published in Nature Mental Health, MS was significantly positively associated with increased MDD risk in the US. This study was based on a multicenter, longitudinal clinical and radiological database that examined the health records data from 281 patients with MS in 2022. Data on magnetic resonance imaging, depression scores, and disability scores was analyzed. Researchers identified that the lesion of MS in the brain and depression have a common pathway and there is a functional connection between MS lesions and the depression circuit in the brain. Patients with MS lesions connected to the depression circuit had significantly higher depression scores.

MDD and MS are significant health burdens in the US. GlobalData epidemiologists forecast MS diagnosed prevalent cases in 2023 of 800,000 in the US, which will increase to 825,000 in 2028. GlobalData epidemiologists also forecast almost 28 million 12-month total prevalent cases of MDD in the US by the end of 2023. The increase in the number of cases of MS can be attributed to the projected increase in the population in the US during the forecast period, as well as the high prevalence of coexisting conditions such as MDD.

MDD can worsen MS symptoms, reduce quality of life, and accelerate death in MS patients. Although this study shows that the functional relationship between MS and MDD exists, it is an exploratory study only, and a detailed study with a large patient sample is required to fully understand the mechanism of association.