2018Research into comorbidity has expanded exponentially in recent years, with over 55,000 papers published in the medical literature over the past seven years, according to a new analysis of the Web of Science database of biomedical publications (Catala-Lopez et al. PLoS One 2018;13:e0189091). The literature search terms included “comorbidity”, in which there is another medical condition in addition to an index disease; as well as the emerging “multimorbidity”, a more patient-centric term in which no index disease is defined and all conditions are viewed with equal importance. Several neologisms have been coined less successfully, such as “multipathology”, “polymorbidity”, “polipathology”, and “pluripathology”.
Overall, 19.3% of papers on comorbidity appeared in psychiatry journals, and 10.8% were published in clinical neurology journals. The journals most likely to publish an article on comorbidity were PLoSOne, the Journal of Affective Disorders (both with over one thousand articles), and the Journal of Clinical Psychiatry (over 700 articles).
The most common medical condition in the comorbidity literature was clinical depression. “Depression” was the most common comorbidity across several disciplines, including Psychiatry, Neurology/Neurosciences, General and Internal Medicine, Geriatrics, Pharmacology, Endocrinology, and Public/Environmental/Occupational Health.
The most prolific authors were Dr. Ronald C Kessler from Harvard Medical School, with 331 articles on comorbidity; his Harvard colleague Dr. Joseph Biederman (248 articles); and Dr. Stephen V Faraone from State University of New York Upstate Medical University (227 articles).
Most publications on comorbidity were written by researchers in the U.S. (37,524), the U.K. (7344), Germany (6899) and Canada (5706). Canadian authors were the most frequent collaborators on U.S. publications; and Canadians also scored high on the number of papers published per capita (159 per million population), The highest number of publications per capita was recorded by researchers in Denmark (297.6/million).
The most cited paper on comorbidity was by Charlson et al, which described a new method of classifying prognostic comorbidity in longitudinal studies (J Chronic Dis 1987;40:373-383); the paper has been cited over 15,000 times. Ronald Kessler was lead author of five of the top 10 most-cited papers, with his series on psychiatric disorders in the National Comorbidity Survey (Arch Gen Psychiatry 1994;51:8-19. Arch Gen Psychiatry 2005;62:593-602. Arch Gen Psychiatry 1995;52:1048-1060. Arch Gen Psychiatry 2005;62:617-627. JAMA 2003;289:3095-3105).
“Comorbidity” first appeared in the medical literature in 1970 (Feinstein AR. J Chronic Dis 1970;23:455-468). It was a concept that grew slowly: only three publications addressed the topic in the 1970s, and 52 in the 1980s. During the 1990s, the number of publications increased to 4179, then to 26,719 in 2000-2009, and 55,051 in 2010-2016.
The authors noted that the growing number of publications on comorbidities reflects the challenge of an aging population and the increased complexity of chronic illnesses. Also important has been the increasing recognition of the comorbidity of mental disorders with substance use disorders, cardiovascular disease, cancer and chronic disorders in recent decades.