Psychiatric disorders comorbid with general medical and functional somatic disorders: The Lifelines cohort study

Objective  
 It is not clear why psychiatric disorders are more prevalent in the functional somatic syndromes than other general medical disorders. This study assessed the correlates of psychiatric disorders in 3 functional syndromes and 3 general medical disorders in a population-based sample.
Methods 
The Lifelines cohort study included 122,366 adults with relevant data for 6 self-reported conditions: irritable bowel syndrome (IBS), fibromyalgia, chronic fatigue syndrome (CFS), inflammatory bowel disease, rheumatoid arthritis, and diabetes. For each condition the proportion with a DSM-IV psychiatric disorder was assessed. In a cross-sectional design logistic regression identified the variables most closely associated with psychiatric disorder in each condition. In a separate sample the prevalence of psychiatric disorder prior to onset of these conditions was assessed.
Results
 The prevalence of psychiatric disorder was higher (17-27%) in the functional somatic syndromes than the general medical disorders (10.4-11.7%). The variables most closely associated with psychiatric disorder were similar in the functional syndromes and general medical disorders:  stressful life events, chronic personal health difficulties, neuroticism, poor perception of general health, impairment of function due to physical illness and reported previous (lifetime) psychiatric disorder.  The prevalence of psychiatric disorder prior to development of these disorder was similar to that of established disorders. 
 Conclusion
 Despite the difference in prevalence, the correlates of psychiatric disorders were similar in functional and general medical disorders and included predisposing and environmental factors. The increased rate of psychiatric disorder in functional somatic syndromes appears to be evident before onset of the syndrome.  
Abbreviations: FM= fibromyalgia,  IBS= Irritable bowel syndrome,  CFS = chronic fatigue syndrome,  RA = Rheumatoid arthritis, OR =Odds Ratio, SCL= Symptom checklist, PSQI = Pittsburgh Sleep Quality Inventory.
Keywords: Fibromyalgia, chronic fatigue syndrome, epidemiology, risk factors.