Preliminary investigation of cognitive function in aged multiple sclerosis patients: Challenges in detecting comorbid Alzheimer's disease

Background: Cognitive impairment can be seen in patients of all ages with multiple sclerosis (MS). However, there is limited research on neurocognitive disorder in older adults with MS and how to detect Alzheimer's disease (AD) or its prodromal stage, amnestic mild cognitive impairment (aMCI). Thus, the MS clinician is challenged to discriminate between signs of MS-related cognitive decline versus a secondary neurodegenerative process. Objective: Compare cognition in older MS patients to patients with AD and aMCI. Methods: We evaluated cognitively impaired and unimpaired MS patients, AD patients, aMCI patients, and healthy controls (HCs), all elderly (n = 20 per group). AD and aMCI diagnoses were derived by consensus conference independent of the MS research project. Neuropsychological measures assessed domains commonly affected in AD, including verbal memory and expressive language. Results: Cognitively impaired and unimpaired MS groups did not differ on any measures sensitive to AD. Unimpaired MS patients were comparable to HCs. Impaired MS patients showed decreased semantic fluency, similar to aMCI patients. Lastly, while both AD and aMCI groups had deficient memory retention, there was no evidence of a retention deficit in either MS group. Conclusion: Our findings suggest that the cognitive profiles of MS and AD are distinct. In contrast to AD, MS is not associated with impairment of memory consolidation. However, there may be overlap between cognitive deficits related to MS and aMCI. Thus, evidence of poor memory retention, in an older MS patient may merit comprehensive dementia evaluation. The study is preliminary and includes no AD biomarkers (e.g., amyloid imaging) to confirm or rule out AD pathology.