Sensory Modulation Disorder as a Diagnostic Marker in Fibromyalgia: Associations with Stress and Symptom Severity

Background/Objectives: Fibromyalgia (FM) is a nociplastic pain disorder marked by altered central nervous system processing and abnormal sensory modulation. Diagnosis remains largely symptom-based and lacks objective biomarkers. Sensory modulation disorder (SMD)—impaired regulation of responses to non-noxious input—may represent a clinically relevant diagnostic dimension. This study aimed to estimate the prevalence/diagnostic value of SMD in FM, examine links with symptom severity and stress, and assess its potential for patient stratification. Methods: In this cross-sectional study, 182 adults were enrolled (104 FM; 78 controls). Standardized instruments included the Adolescent/Adult Sensory Profile (AASP), Fibromyalgia Impact Questionnaire (FIQ), and Perceived Stress Scale (PSS). Group comparisons, regression, and discriminant analyses evaluated SMD profiles. Results: Compared with controls, FM adults showed higher sensory sensitivity and avoidance (both p < 0.001), lower sensation seeking (p = 0.002), and modestly higher low registration (p = 0.027). Elevated SMD correlated with greater symptom severity and perceived stress. Stress significantly predicted FM’s impact (β = 0.57, p < 0.001). A discriminant model achieved 84% apparent in-sample accuracy for classifying FM severity from sensory/stress profiles. Conclusions: Sensory modulation abnormalities are highly prevalent in FM and show meaningful associations with symptom severity and stress, suggesting that SMD could represent a potential diagnostic dimension and stratification aid. These findings should be interpreted within an exploratory, cross-sectional design. Incorporating sensory modulation assessment into FM evaluation may improve diagnostic precision, reduce delays, and guide individualized management. Confirmation in larger longitudinal studies is warranted.