Research on patients with multiple health conditions: different constructs, different views, one voice

Technological advances, improvements in medical care and public health policies have resulted in a growing proportion of patients with multiple health conditions. The prevalence of multiple health conditions among individuals increases with age, is substantial among older adults, and will increase dramatically in coming years [1?4]. This phenomenon has received growing interest in the most recent literature and has led to several ? and often differing ? conceptualizations. The term “comorbidity” was originally defined by Feinstein as “any distinct additional clinical entity that has existed or may occur during the clinical course of a patient who has the index disease under study” [5]. This definition places one disease in a central position and all other condition(s) as secondary, in that they may or may not affect the course and treatment of the index disease [6]. Feinstein’s principle has been applied all too readily as if the effect of comorbidity was secondary or indeed negligible. In clinical research, individuals with a narrowly defined index condition and no major comorbidities are usually enrolled, leaving the majority of the patients seen in a typical family practice [7,8] out in the cold. In clinical practice, management of the index condition invariably takes priority, with disjointed ? if any ? treatment plans developed for each of the comorbidities [6]. This model of care is typical of delivery systems constructed around specialized care, where areas of expertise are defined around specific conditions and bodily systems [11]. Not surprisingly, clinical practice guidelines arising from that model of care lack pertinence for patients with multiple health conditions [9,10].