Mentalising impairments in somatic symptom and functional neurological disorders: A systematic review.

Somatic Symptom Disorder (SSD) and Functional Neurological Disorder (FND) are among the most prevalent conditions within the DSM-5 category of somatic symptom and related disorders (SSRD) and are associated with substantial psychological distress and functional impairment. Although the aetiology of SSRD is multifactorial and remains uncertain, emerging evidence suggests that impairments in mentalizing - the capacity to understand one's own and others' mental states - may contribute to the development and persistence of functional somatic symptoms. Despite growing research interest, no systematic review has synthesised the evidence comparing mentalizing abilities in individuals with SSD or FND to those without these diagnoses. The present systematic review addressed this gap by examining whether individuals with SSD and FND differ in mentalizing relative to healthy and clinical control groups, focusing on studies explicitly assessing mentalizing-related constructs. A comprehensive search of three electronic databases identified 18 eligible studies, comprising 1801 participants. Methodological quality was appraised using the Joanna Briggs Institute (JBI) Critical Appraisal Tool for case-control studies, and the psychometric robustness of mentalizing measures was critically evaluated. Overall, adults with SSD and FND - particularly those with psychogenic non-epileptic seizures (PNES) - demonstrated impairments in other-focused cognitive mentalizing compared to control groups. In contrast, self-focused mentalizing was rarely assessed, precluding firm conclusions. Findings suggest that mentalizing may be clinically relevant in SSD and FND and support further investigation of mentalization-informed assessment and intervention. However, substantial diagnostic and measurement heterogeneity underscores the need for high-quality, adequately powered studies employing validated, multidimensional assessments of mentalizing.