Cognitive Impairment in Secondary Progressive Multiple Sclerosis: Effect of Disease Duration, Age, and Progressive Phenotype

Background: Cognitive deficits are common in multiple sclerosis (MS) and affect patients at all stages of the disease, regardless of phenotype. Aims: This literature review focuses the cognitive deficits observed in secondary progressive MS (SPMS). It is mainly based on studies that compared the frequency and main characteristics of cognitive deficits in SPMS with other phenotypes. Methods: A bibliographic search was carried out using the PubMed database with the following keywords: multiple sclerosis, secondary-progressive, cognition. Results: Thirteen studies were initially selected that were published in English, reporting the neuropsychological data of a sample of at least 30 patients with SPMS, comparing them with patients with other phenotypes. Studies suggest that there is an association between the duration of the disease and the frequency and extent of the cognitive disorders. Studies also showed that the SP form is associated with an increased frequency of cognitive impairment and with an increased severity as compared to relapsing-remitting MS (RRMS). Compared to RRMS, progressive forms of MS are associated with more severe impairment in certain cognitive areas, such as episodic verbal memory, information processing speed, working memory, or verbal fluency. Two studies showed that cognitive performances decline overtime in SPMS. Conclusion: Cognitive disorders are more frequent and more severe in the SP form than in relapsing course of MS. The profile of cognitive impairment encountered in the SP form also appears to be different from those found in the other phenotypes.