Reliability of the Apathy Evaluation Scale in Myotonic Dystrophy Type 1

Apathy is a common debilitating symptom of myotonic dystrophy type 1 (DM1). The Apathy Evaluation Scale (AES) has been identified as a promising measurement instrument to be used in DM1 but its metrological properties must be further documented.

To determine the internal consistency of the Self (AES-S), Informant (AES-I), and Clinician (AES-C) versions of the AES and to assess the test-retest reliability, standard error of measurement, and minimal detectable change of the AES-S and AES-I in a sample of DM1 patients and their related informants.

All scales showed good internal consistency (Cronbach's alpha: 0.83-0.87) and the AES-S and AES-I showed good test-retest reliability (ICC = 0.79-0.91). Additionally, clinicians and informants had a tendency to overestimate DM1 patients' level of apathy compared to patients' self-ratings, suggesting potentially impaired self-awareness in DM1 patients.

The present results advocate the use of the AES-I as a reliable instrument to estimate apathy in DM1 patients for either clinical or research purposes, and support the relevance to pursue the assessment of metrological properties of the AES as a tool of great value for the development of outcomes for clinical trial readiness in DM1.