Figure 1.

Terminologies most commonly used in different neurodegenerative diseases. Different fields have used different terms to describe the prodromal phase of disease that precedes clinically overt disease. For Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD) and FTD, this period is designated as MCI, prodromal Parkinson’s disease, prodromal Huntington’s disease and prodromal FTD, respectively. In some parlance, prodromal FTD encompasses both MCI-cognition and MCI-behaviour. Similarly, each of these disorders is also characterized by an even earlier stage of asymptomatic disease (pre-MCI, preclinical Parkinson’s disease, pre-symptomatic Huntington’s disease and preclinical FTD, respectively), during which clinical symptoms and signs are absent, but biomarker evidence may be present. Terminology for SMA is less well-defined.