The Canadian Alzheimer Disease Review • June 2002 • 15 T he study of cognitive changes with aging has grown expo- nentially over the past few years. At one end of the spectrum is Alz- heimer’s disease (AD), for which the best estimates of lifetime risk range from 14.5% to 26.2% of the population. 1 The Canadian Study of Health and Aging (CSHA) has estimated the prevalence of dem- entia to be 8% in the population over the age of 65 years. 2 At the other end of the spectrum are changes in cognitive performance that now are classified as normal. Over a two-year period, retesting elderly patients using memory tests revealed that approximately one third of them had subtle but measurable memory decline over time. 3 On the WAIS-R IQ scale, an 85-year-old can achieve a score of 100 by correctly answering only half as many questions as a 21-year-old. Hence, before claim- ing that an elderly person shows “cognitive impairment,” it is best to compare that person to a group of individuals similar in age. Definitions Mild memory problems, falling between the two poles of “normal” and “dementia,” are a common phe- nomenon in older people. The CSHA documented a 16.8% preva- lence of cognitive impairment with- out dementia in the elderly. 4,5 Currently, the most widely used term to characterize this group is “mild cognitive impairment” (MCI), derived from the World Health Organization (WHO) and adapted by a number of centres. 6-8 MCI is a clinical label which includes elderly subjects with short-term or long- term memory impairment and with no significant daily functional dis- ability. The original diagnosis of MCI required a subjective report of cognitive decline from a former level, gradual in onset, and present for at least six months. This subjec- tive complaint required supplemen- tation with objective evidence of memory and learning decline, with other cognitive domains remaining “generally intact.” 9 There was no clear delineation as to how the pres- ence of memory loss was to be established. In all cases, the term MCI excluded individuals with sig- nificant depression, delirium, men- tal retardation, or other psychiatric disorders likely responsible for the impairment. If the memory loss was severe and accompanied by signifi- Mild Cognitive Impairment by Howard Chertkow, MD, FRCPC Dr. Chertkow is a Neurologist in the Departments of Neurology & Neurosurgery and Geriatric Medicine at the Sir Mortimer B. Davis-Jewish General Hospital. He also is Director of the Bloomfield Centre for Research in Aging, Lady Davis Institute for Medical Research, McGill University and co-directs the Jewish General Hospital/McGill Memory Clinic, Montreal, Quebec. CASE STUDY: Mr. C is a 63-year-old executive who presents to you complaining of memory loss. The problem began insidiously over the past year and he believes it has been getting worse. He previously had difficulty remembering the names of occasionally-seen employees, but now even the details of important current accounts and recent meetings escape him. He has started keeping copious notes and lists, and double-checking details with his secretary and wife (who confirms the memory decline). There has been no impact on his functional abilities at work and, according to him and his wife, he remains otherwise cognitively intact. Mr. C denies experiencing depression. He admits to a high level of stress at work, poor sleep, occasional use of sedatives, but no alcohol consumption. He is in good health, with controlled hypertension. There is no history of transient ischemic attack (TIA) or cerebral infarction. Physical examination is normal and his Folstein Mini-Mental State Examination (MMSE) score is 28 (he only recalled one of three words after a delay). His basic bloodwork results— including B12, folate, thyroid-stimulating hormone (TSH) and electrolytes—are normal, as is a computed tomography (CT) scan. He asks you for prognosis and treatment, and wonders whether he should retire.