The origin, development and current concepts of «comorbidity» and «polymorbidity»

The article aims to study the current concepts of polymorbidity and comorbidity by a literature review. This article presents the terms used to denote a combination of several diseases for one person, named as «combined», «concomitant», «associated» diseases or conditions, «comorbidity», «polymorbidity», «multimorbidity», «multifactorial disease», «polypathia», «co-disease», «dual diagnosis», «plural diseases». Definitions for currently commonly used terms «comorbidity», «polymorbidity» and «multimorbidity» are given, the historical aspects of their occurrence are discussed. The differences between the concepts of «comorbidity» and «polymorbidity», despite their frequent use as synonyms, are listed. The existing classifications of comorbidity, including definitions of trans-systemic, trans-nosologic and chronological comorbidity, are reviewed. The classification developed by H.C. Kraemer and M. van den Akker (1998), which presents a causal, complicated, iatrogenic, unclear and random comorbidity, is described. The assessment scales for the evaluation of this phenomenon, such as Cumulative Illness Rating Scale, Kaplan-Feinstein index, Cumulative Illness Rating Scale for Geriatrics, Index of Co-Existent Disease, Geriatric Index of Comorbidity, Functional Comorbidity Index, and Total Illness Burden Index, are presented. Detailed description of the comorbidity assessment by Charlson index as the most used and having the least disadvantages, is given. Description of the quantitative evaluation of polymorbidity is given, variation of the number of diseases depending on patient’s age is shown. The list for the most common pathologies that can be combined in a single patient is outlined. Diseases typical for the patients of elderly and senile age are described. The problem of comorbidity becomes more and more important in the areas where social conditions promote the increase of the life expectancy of elderly and senile patients, which requires a common approach to the problems of comorbidity.