The prodromal phase of sporadic Parkinson's disease: does it exist and if so how long is it?

It is frequently assumed that idiopathic Parkinson's disease starts with several nonmotor symptoms and signs, but the evidence for this stage in the disease process is of variable quality. This review evaluates the more robust prospective or pathologically confirmed publications to establish whether there is a premotor period and if so what is its duration. The most informative studies are considered to be those concerned with olfaction, dysautonomia, and sleep disorder. Estimates for the duration of the prodromal phase vary from months to decades. It is concluded that there probably is an early phase in the disease where a variety of nonmotor features develop, but the sequence and time of onset of such features is not well established. (c) 2008 Movement Disorder Society.