Understanding General Somatic Symptom Burden: Insights from a Systematic Review of Factor Analyses Pertaining to the Patient Health Questionnaire 15 (PHQ-15) and Somatic Symptom Scale 8 (SSS-8).

Background: Factor analyses have indicated that somatic symptom burden can be separated into local symptom domain factors (e.g., cardiopulmonary, fatigue, gastrointestinal, pain) and a general propensity toward being symptomatic. This study aimed to determine what specific physical symptoms, and correlates, that are most strongly associated with this general factor.

Method: A systematic review was based on factor analyses of the Patient Health Questionnaire 15 (PHQ-15) and Somatic Symptom Scale 8 (SSS-8).

Results: There was heterogeneity in the included studies, in terms of the exact specification of the factor structure, and to some extent regarding item inclusion for factor analysis. Among 11 analyses of the PHQ-15, the highest mean and median factor loadings on the general symptom burden factor were seen for fatigue (M = 0.65) followed by dizziness (0.63). Among three analyses of the SSS-8, the mean was highest for chest pain and shortness of breath (0.69), followed by fatigue (0.62). The PHQ-15 general factor exhibited variable, but usually moderate to strong, associations with anxiety and depression symptoms, health anxiety, somatosensory amplification, and functional somatic syndromes.

Conclusions: Cardiopulmonary symptoms and fatigue appear to be especially closely associated with general somatic symptom burden. The close associations between this general factor and indicators of poor mental health and functional somatic syndromes allow for numerous interpretations; both causal and due to overlapping definitions.