Cognitive Impairment and Autobiographical Memory in Elderly Patients with Multiple Sclerosis – Subtype Classification and Comparison with Alzheimer’s Disease

Multiple sclerosis (MS) is one of the most common neurological diseases of the early and middle adulthood and is characterized by inflammatory demyelination and axonal injury in the brain and spinal cord. Whereas inflammatory demyelination traditionally has been seen as the main disease process in MS, axonal damage or loss is receiving increasing attention. In MS brain atrophy affects extensively the white matter and cortical and deep grey matter structures and is closely related to the presence and severity of cognitive impairment. Since neuropsychological examination of elderly patients with MS is not a main focus of current research there are many unresolved questions regarding magnitude and pattern of deficits in this disease. Particularly controversies exist whether deficits are indicative of clinical course and subtype classification. Moreover, Alzheimer’s disease-related pathology cannot be ruled out in elderly MS patients as advancing age is the most significant risk factor for developing Alzheimer dementia (AD). Both patients with amnestic mild cognitive impairment (aMCI) or dementia due to Alzheimer's disease and MS show axonal loss and neurodegeneration in cortical areas that are involved in cognitive processing. Similar to Alzheimer's disease these neuropathological changes worsen over time and seem to increase cognitive deterioration in long-term patients with progressive MS subtypes. The presented work aimed to distinguish MS-related cognitive impairment from Alzheimer's disease-related deficits and to characterize disease-dependent deterioration patterns by comparing age-, education-, and gender-matched groups of elderly patients with relapsing-remitting MS (RRMS), secondary progressive MS (SPMS), aMCI, or early AD using the Autobiographical Memory Interview (AMI) and the German version of the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) test battery. We found substantial episodic memory deficits in the long-term course of SPMS that were associated with deterioration of executive function, but not impairment of memory storage as recognition was preserved in SPMS in contrast to the patients with aMCI. Furthermore, patients with SPMS, AD, and aMCI, but not with RRMS, exhibited a pattern of episodic autobiographical memory impairment that followed Ribot's Law; older memories were better preserved than more recent memories. In contrast to aMCI and AD, neither SPMS nor RRMS were associated with semantic autobiographical memory impairment. In summary, our neuropsychological results point at distinct disease mechanisms in different MS subtypes and differentiate between MS-related cognitive impairment and AD-related deficits. Neuropsychological testing may contribute to identify AD-related pathology in SPMS patients since MS-related episodic memory impairment due to deteriorated executive function can be distinguished from AD-related encoding and storage deficits. Moreover, possibly due to neurodegenerative processes in functional relevant brain regions deficits in episodic autobiographical memory are affected in long-term patients with SPMS similarly to that seen in patients with AD or aMCI.

Author

• Müller, Stephan

Identifier

hdl:10900/49776

OAI record oai:identifier

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