Efficacy of cognitive rehabilitation therapies for mild cognitive impairment (MCI) in older adults: working toward a theoretical model and evidence-based interventions

Abstract

To evaluate the efficacy of cognitive rehabilitation therapies (CRTs) for mild cognitive impairment (MCI). Our review revealed a need for evidence-based treatments for MCI and a lack of a theoretical rehabilitation model to guide the development and evaluation of these interventions. We have thus proposed a theoretical rehabilitation model of MCI that yields key intervention targets-cognitive compromise, functional compromise, neuropsychiatric symptoms, and modifiable risk and protective factors known to be associated with MCI and dementia. Our model additionally defines specific cognitive rehabilitation approaches that may directly or indirectly target key outcomes-restorative cognitive training, compensatory cognitive training, lifestyle interventions, and psychotherapeutic techniques. Fourteen randomized controlled trials met inclusion criteria and were reviewed. Studies markedly varied in terms of intervention approaches and selected outcome measures and were frequently hampered by design limitations. The bulk of the evidence suggested that CRTs can change targeted behaviors in individuals with MCI and that CRTs are associated with improvements in objective cognitive performance, but the pattern of effects on specific cognitive domains was inconsistent across studies. Other important outcomes (i.e., daily functioning, quality of life, neuropsychiatric symptom severity) were infrequently assessed across studies. Few studies evaluated long-term outcomes or the impact of CRTs on conversion rates from MCI to dementia or normal cognition. Overall, results from trials are promising but inconclusive. Additional well-designed and adequately powered trials are warranted and required before CRTs for MCI can be considered evidence-based.

Fig. 1. Theoretical rehabilitation model of mild cognitive impairment (MCI) to guide the development and evaluation of cognitive rehabilitation therapies (CRTs) for MCI

In this provisional rehabilitation model, MCI is viewed as an intermediate stage between normal cognition and dementia. Individuals with MCI may alternatively return to normal cognition or present with a persistent MCI that does not convert to dementia. The etiology of MCI and dementia are viewed as multifactorial, and a range of risk and protective factors, including those listed in Table 1, contribute toward increased or decreased risk, respectively. In some individuals, the cumulative and interactive impact of these factors on the brain results in the behavioral manifestation known as MCI which is characterized by three types of symptoms: (a) mild cognitive compromise (measured by objective neuropsychological tests), (b) mild functional compromise not yet precluding independent living (evaluated by measures of daily functioning and quality of life), and (c) commonly associated neuropsychiatric symptoms such as depression, anxiety, fatigue, and sleep difficulties (measured by neuropsychiatric symptom severity scales). Based on this model, the figure identifies the key intervention targets that CRTs for MCI are likely to address. Specifically, CRTs can target the symptoms of MCI (i.e., cognitive compromise, functional compromise, or associated neuropsychiatric symptoms). Or, they may target modifiable risk and protective factors, particularly the lifestyle factors that are highlighted in the figure because they are known to increase (depicted as arrows with plus signs) or decrease (depicted as arrows with negative signs) risk for MCI and dementia. In a clinical trial, appropriate intervention outcomes would include reducing MCI symptoms (i.e., symptom management), reducing the conversion rate from MCI to dementia (i.e., preventing dementia), or increasing the conversion rate from MCI to normal cognition (i.e., curing MCI).