Objective: To investigate longitudinal change in the medical decision-making capacity (MDC) of patients with amnestic mild cognitive impairment (MCI) under different consent standards.Methods: Eighty-eight healthy older controls and 116 patients with MCI were administered the Capacity to Consent to Treatment Instrument at baseline and at 1 to 3 (mean ϭ 1.7) annual follow-up visits thereafter. Covariate-adjusted random coefficient regressions were used to examine differences in MDC trajectories across MCI and control participants, as well as to investigate the impact of conversion to Alzheimer disease on MCI patients' MDC trajectories.Results: At baseline, MCI patients performed significantly below controls only on the three clinically relevant standards of appreciation, reasoning, and understanding. Compared with controls, MCI patients experienced significant declines over time on understanding but not on any other consent standard. Conversion affected both the elevation (a decrease in performance) and slope (acceleration in subsequent rate of decline) of MCI patients' MDC trajectories on understanding. A trend emerged for conversion to be associated with a performance decrease on reasoning in the MCI group. Conclusions: Medical decision-making capacity (MDC) decline in mild cognitive impairment (MCI)is a relatively slow but detectable process. Over a 3-year period, patients with amnestic MCI show progressive decline in the ability to understand consent information. This decline accelerates after conversion to Alzheimer disease (AD), reflecting increasing vulnerability to decisional impairment. Clinicians and researchers working with MCI patients should give particular attention to the informed consent process when conversion to AD is suspected or confirmed. Neurology ® 2008;

Persons with amnestic mild cognitive impairment (MCI) have subtle impairments in medical decision-making capacity (MDC). We examined the relationship between proton magnetic resonance spectroscopy (MRS) and MDC in MCI. Twenty-nine MCI patients and 42 controls underwent MRS to obtain ratios of N-acetylaspartate (NAA)/Creatine (Cr), Choline (Cho)/Cr, and myo-Inositol (mI)/Cr of the posterior cingulate. They also completed the Capacity to Consent to Treatment Instrument (CCTI), a vignette-based instrument measuring decisional standards of expressing choice, appreciating consequences of choice, providing rational reasons for choice, and understanding treatment choices. Patients showed abnormal MRS ratios of mI/Cr and Cho/Cr compared to controls, and impairments on the CCTI understanding and reasoning Standards. Performance on the Reasoning Standard of the CCTI was correlated with NAA/Cr (r = 0.46, p < 0.05). The relationship of NAA/Cr with decision-making suggests a role for posterior cortical neuronal functioning in performance of complex IADLs in MCI.