Determining the Minimal Clinically Important Difference in Somatic Symptom Scale-8 Score in Patients With Somatic Symptoms and Related Disorders: A Six-Month Follow-Up Study.

Background/Objective: Whether changes in Somatic Symptom Scale-8 (SSS-8) scores adequately reflect subjective improvement in patients with somatic symptoms and related disorders (SSRD) at follow-up is unclear. The minimal clinically important difference (MCID) is a criterion of estimating clinically significant improvement derived from patients' responses to anchor questions that accurately reflect changes in their condition. This study aimed to clarify the MCID value of the SSS-8 for SSRD. Methods: Patients with SSRD aged 18 to 84 years who attended a university hospital outpatient department in Japan were eligible. The participants were assessed using the SSS-8 for physical symptoms. After approximately 6 months of outpatient treatment, the participants were reassessed using the SSS-8 for physical symptoms. The primary endpoint was the Patient Global Impression of Change score. The secondary endpoint was the physical function items of the Multidimensional Patient Impression of Change questionnaire. These questionnaires were used to define improvements in subjective symptoms as the anchor to estimate the MCID. Receiver operating characteristic analysis was performed based on the anchor questions and the MCID values of the SSS-8 were calculated. Results: Ninety participants were included. The primary endpoint MCID value for the SSS-8 was -6 points, with an area under the curve (AUC) of 0.87, 65.9% sensitivity, and 93.5% specificity. The secondary endpoint MCID value for the SSS-8 was -6 points, with an AUC of 0.85, 76.5% sensitivity, and 89.3% specificity. Conclusion: The SSS-8 is a useful indicator for SSRD clinical outcomes. Patients with SSRD may need an SSS-8 score decrease of 6 or more points to notice symptom improvements.