Caudate volume and symptoms of apathy in older adults with multiple sclerosis

Background: Apathy is common in multiple sclerosis (MS) and neurological disease, but its presence and underlying brain mechanisms in older adults with MS (OAMS) have not been evaluated. Objective: Examine apathy and its association with caudate nuclei volume in OAMS and controls. We hypothesized that compared to controls, OAMS would demonstrate: a) greater apathy; b) stronger associations between apathy and caudate nuclei volumes. Methods: OAMS (n = 67, mean age = 64.55 ± 3.89) and controls (n = 74, mean age = 69.04 ± 6.32) underwent brain MRI, cognitive assessment, psychological, and motoric testing. Apathy was assessed through the apathy subscale of the 30-item Geriatric Depression Scale. Results: OAMS reported greater apathy compared to controls (β = 0.281, p = 0.004). Adjusted moderation analyses revealed a significantly stronger association between caudate volume and apathy (left: B = −1.156, p = 0.039, right: B = −1.163, p = 0.040) among OAMS compared to controls. Conditional effects revealed that in adjusted models, lower volume of both the left (b = −0.882, p = 0.037) and right (b = −0.891, p = 0.038) caudate nuclei was significantly associated with greater apathy only among OAMS. Conclusion: Caudate nuclei, which are susceptible to adverse MS effects and implicated in mediating cognitive and motor function, may influence the presence and severity of apathy in OAMS.