Reliability and construct validity of the Italian version of AMAT scale in SBMA subjects

Background: Spinal and Bulbar Muscular Atrophy (SBMA) is a rare X-linked polyglutamine disorder characterized by a CAG trinucleotide repeat expansion in the androgen receptor gene. This leads to progressive lower motor neuron degeneration and skeletal muscle atrophy. Given the need for sensitive outcome measures in clinical trials, this study aimed to perform the linguistic adaptation and psychometric validation of the Adult Myopathy Assessment Tool (AMAT) for the Italian population. Methods: Following a rigorous forward-back translation protocol to ensure semantic and conceptual equivalence, the Italian AMAT was administered to 29 patients. The validation process assessed internal consistency (Cronbach’s alpha), inter-rater and intra-rater reliability, and construct validity. The latter was evaluated through correlations with established clinical markers, including the Six-Minute Walk Test (6MWT), the SBMA Functional Rating Scale (SBMAFRS), and the ALSAQ-40 scale. Results: Psychometric analysis revealed excellent inter- and intra-rater reliability and strong internal consistency (Cronbach’s alpha > 0.70). Construct validity was confirmed through significant correlations with established functional markers, including the six-minute walk test (6MWT) and the SBMA Functional Rating Scale (SBMAFRS), while the expected negative correlations with ALSAQ-40 scale physical domains—coupled with a lack of correlation with the communication domain—affirmed divergent validity. Conclusions: The Italian version of the AMAT is a reliable and valid instrument for quantifying functional impairment and endurance in SBMA. Its implementation facilitates standardized longitudinal assessment and enhances the feasibility of cross-national collaborative research.