Imaging Retinal Amyloid — The Virtual Brain Biopsy

Introduction

Alzheimer’s disease (AD) is the most common cause of dementia with a worldwide prevalence of about 25 million in 2010 and is expected to double by 2030 because of increased life expectancy . The traditional diagnosis of AD connotes “Alzheimer’s disease dementia” — when the disease is in the late stage . More recently, the clinical disease stages of AD have been divided into three phases. First is a pre-symptomatic phase in which individuals are cognitively normal but some have AD pathological changes.

Labeling these individuals as having pre-symptomatic AD is conjecture rather than fact, as some of these individuals will die without ever expressing clinical symptoms. The hypothetical assumption is that an asymptomatic individual with pathological changes that are indicative of AD would ultimately have become symptomatic if he or she lived long enough. Second is a prodromal phase of AD, commonly referred to as Mild Cognitive Impairment (MCI) , which is characterized by the onset of the earliest cognitive symptoms (typically deficits in episodic memory) that do not meet the criteria for dementia.

The severity of cognitive impairment in the MCI phase of AD varies from the earliest appearance of memory dysfunction to more widespread dysfunction in other cognitive domains. The final phase in the evolution of AD is dementia is impairment that is severe and produces loss of function. Diagnostic certitude in AD in only attained at autopsy or via a brain biopsy.