Neurocognitive patterns and progression of mild cognitive impairment with Lewy bodies or Alzheimer’s disease

Abstract

Mild cognitive impairment is a heterogeneous condition; while typically viewed as the transition stage between healthy cognitive function and dementia, the cognitive and clinical patterns of this condition vary, as do its prognosis. The two most common neurodegenerative dementias, dementia with Lewy bodies and Alzheimer’s disease, differ in their clinical features, patterns of cognitive impairment, and prognosis. It is not known whether the respective mild cognitive impairment stages preceding onset of dementia also differ in these characteristics. Two cohorts of people with recent mild cognitive impairment diagnosis were assessed, undergoing annual review of cognition, diagnosis and presence of clinical features of Lewy body disease by an expert panel of old age psychiatrists, and repeated imaging, to reach a consensus diagnosis of either mild cognitive impairment due to Alzheimer’s disease, or with Lewy bodies, in line with current consensus criteria for these. Making use of annually repeated cognitive assessment and clinical diagnostic information, the longitudinal progression of these two conditions was characterised with flexible statistical methods, using the first cohort for model development, and the second for validation: different trajectories of decline in specific cognitive domains were observed in the diagnostic groups, reflecting typical patterns of impairment in their respective dementia syndromes. Mild cognitive impairment with Lewy bodies was also observed to have a worse prognosis, in keeping with its dementia stage, with a greater risk of progressive cognitive decline, and faster onset of dementia. Individuals with neuropsychiatric symptoms (cognitive fluctuations and visual hallucinations) were also at more risk of decline than those with slower-developing features (REM sleep behaviour disorder or parkinsonism) or those with Alzheimer’s disease. Mild cognitive impairment with Lewy bodies may therefore feature early cognitive, clinical, and prognostic differences from Alzheimer’s disease, reflecting its eventual dementia syndrome.