The number of existing functional somatic syndromes (FSSs) is an important risk factor for new, different FSSs.

OBJECTIVE: The objective of this study is to test the hypothesis that the number of functional somatic syndromes (FSSs) predicts new, additional FSSs.
METHODS: In a recent case-control study of interstitial cystitis/painful bladder syndrome (IC/PBS), we used symptom-based consensus definitions to identify these FSSs: fibromyalgia (FM), chronic fatigue syndrome (CFS), irritable bowel syndrome (IBS), chronic pelvic pain, migraine, sicca syndrome and panic disorder. Those present before the incidence year were called antecedent FSSs; those with onset during the incidence year were called incident FSSs. In each of two groups, 312 IC/PBS cases and 313 controls, rates of incident FSSs were compared among those with 0, 1, 2, or ≥3 antecedent FSSs. Confounding was assessed using logistic regression analyses that included the individual antecedent FSSs, published correlates of these FSSs, and demographic variables.
RESULTS: The incidence of a new FSS increased with the number of antecedent FSSs, as did that of incident FM, CFS and IBS studied separately. These findings were not confounded by other variables. The presence of multiple antecedent FSSs generally had the highest odds ratio for new, different, incident FSSs.
CONCLUSIONS: This study revealed that the number of antecedent FSSs was among the strongest risk factors for other FSSs, especially incident FM, CFS and IBS. This suggests that the FSSs are linked through a polysyndromic phenotype. If each FSS is heterogeneous, to seek a pathogenesis common to all FSSs, individuals with multiple FSSs should be sought; to seek a pathogenesis unique to a specific FSS, mature persons who have only that FSS should be studied.