Cognitive Dysfunction in Fibromyalgia: Prevalence and Independent Predictors—A Case–Control Study Using the Montreal Cognitive Assessment Scale

Background: Cognitive dysfunction is a frequent but under-recognized feature of fibromyalgia (FM). Its prevalence varies widely across studies, and independent clinical predictors remain uncertain. This study aimed to determine the prevalence of cognitive dysfunction in FM patients compared with healthy controls and identify independent associated factors. Methods: We conducted a case–control study including 47 adult female patients with FM (2016 ACR criteria) and 19 age- and sex-matched healthy controls. Sociodemographic and clinical data were collected. Cognitive function was evaluated using the Montreal Cognitive Assessment (MoCA), with cognitive dysfunction defined as MoCA < 26. Pain (VAS), fatigue (VAS and FACIT-F), anxiety and depression (HADS), sleep quality (PSQI), and disease impact (FIQ-P) were assessed. Univariate analysis was followed by binary logistic regression to identify independent predictors of cognitive dysfunction and multiple linear regression to explore associations with MoCA score. Results: Cognitive dysfunction was present in 72.3% of FM patients versus 5.3% of controls (p < 0.001). FM patients had significantly worse pain scores, fatigue levels, psychological distress, sleep quality, and quality of life (all p < 0.001). In FM patients, MoCA scores correlated inversely with pain (r = −0.34), anxiety (r = −0.34), depression (r = −0.48), disease impact (r = −0.43), and sleep disturbance (r = −0.48), and positively with FACIT-F (r = 0.37) and EQ-5D-5L (ρ = 0.60). In multivariate analysis, higher FIQ-P scores were independently associated with cognitive dysfunction [adjusted OR1.18; 95% CI (1.06–1.30); p < 0.01]. Pain severity [adjusted B = −0.40; 95%CI (−0.64–0.15; p < 0.01)] and depression [adjusted B = −2.60; 95% CI (−4.12–1.04; p = 0.001)] were independently associated with lower MoCA scores. Conclusions: Cognitive dysfunction is highly prevalent in FM and is independently associated with pain severity, depressive symptoms, and disease impact.