Predictors of a Functional Somatic Syndrome Diagnosis in Patients with Persistent Functional Somatic Symptoms

Functional somatic syndromes (FSS) are characterized by the existence of multiple persistent functional somatic symptoms. Not many patients fulfilling the criteria for an FSS, receive a formal diagnosis, and it is unknown which factors explain this discrepancy. Patients that tend to worry and patients that gather more health information may have an increased chance of an FSS diagnosis. We hypothesized that high intelligence and high neuroticism increase the probability of an FSS diagnosis in patients with persistent functional somatic symptoms. This study aims to investigate patient factors that might be important in the process of syndrome labeling. Our study was performed in a large, representative population cohort (n = 976) in Groningen, The Netherlands, and included two assessment waves. Intelligence was measured using the General Aptitude Test Battery version B 1002-B. Neuroticism was measured using the 12-item neuroticism scale of the Eysenck Personality Questionnaire-Revised. Functional somatic symptoms were measured with the somatization section of the Composite International Diagnostic Interview. Current FSS diagnosis was assessed with a questionnaire. We performed multivariable logistic regression analyses including sum scores of neuroticism, intelligence scores, sex, number of functional somatic symptoms, and age as potential predictors of having an FSS diagnosis. From the 976 participants that completed measurements at follow-up, 289 (26.4 %) participants reported at least one persistent functional somatic symptom, and these subjects were included in the main analyses (38.4 % males, mean age of 55.2 years (SD = 10.7), 36-82 years). High numbers of functional somatic symptoms ((OR) = 1.320; 95 % (CI) = 1.097-1.588), female sex (OR = 9.068; 95 % CI = 4.061-20.251), and high intelligence (OR = 1.402; 95 % CI = 1.001-1.963) were associated with an FSS diagnosis, while age (OR = 0.989; 95 % CI = 960-1.019) and neuroticism (OR = 0.956; 95 % CI = 0.872-1.048) were not. This study suggests that high intelligence, but not high neuroticism, increases the chance of syndrome labeling in patients with persistent functional somatic symptoms.