Abstract

Most investigators believe that by the time the clinical diagnosis of Alzheimer's disease has been made, sufficient neuronal damage has taken place in the brain to make reversal of the condition unlikely. Prevention would be a more appealing strategy, but the challenges of conducting true primary prevention trials in asymptomatic persons are formidable. The duration and expense of these types of trial make them unappealing. Large numbers of subjects would need to be followed for many years, and without a promising therapeutic agent, this approach would be risky. Hence, the concept of secondary prevention treatment trials involving minimally symptomatic individuals, such as persons with mild cognitive impairment (MCI) — a transitional stage between normal ageing and very early Alzheimer's disease — has evolved and seems more promising. This concept has led to the emergence of a number of clinical trials for MCI, which are discussed here.