Deciphering a Prodrome: Looking for a Disease in a Haystack

: In many chronic diseases, the underlying biological processes begin long before the condition is clinically recognized and diagnosed. After biologic onset of the disease an early, often nonspecific, set of symptoms, or prodrome, may develop before more characteristic symptoms of the disease present. For instance, in Parkinson disease (PD), some of the earliest manifestations, such as smell or taste dysfunction, may occur 2 decades before typical symptoms, such as tremor, appear.1 Generally, the combination of long prodromal phases and nonspecific symptoms hampers early recognition of disease. Recognizing the prodromal phase of a disease in an individual has 2 potential benefits. First, accurate identification of etiologic factors for disease depends on ensuring that the putative exposure preceded biologic onset of the disease and that the identified symptoms are not related to a delay in diagnosis. Therefore, recognition of a prodromal phase may enhance the ability to identify etiologic factors. Second, accurate prediction that an individual is in the prodromal phase of the disease offers the tantalizing possibility that intervention in this phase could prevent or delay evolution of more typical clinical manifestations.2.