Neuromuscular disorders (NMDs) can lead to specific manual disabilities due to hand muscle weakness and atrophy, myotonia, or loss of sensory function. The aim of this study was to adapt and validate the ABILHAND questionnaire in children and adults with NMDs using the Rasch model. This questionnaire contained specific manual activities for children and for adults, as well as common manual activities. One hundred and twenty-four adult patients and the parents of 124 paediatric patients were asked to provide their perceived difficulty in performing each manual activity on a three-level scale: impossible (0), difficult (1) or easy (2). Items were selected from well-established psychometric criteria (ordered categories, equal item discrimination, adequate fit to the Rasch model, lack of redundancy) using the Rasch Unidimensional Measurement Models (RUMM2020((c))) computer programme. The 22 selected items contain 4 children specific items, 4 adult specific items and 14 items commonly applicable to both children and adults. They define a unidimensional and linear measure of manual ability and demonstrate continuous progression in their difficulty. The item hierarchy of difficulty was invariant across six patient-related factors. The scale exhibited good precision (r=0.95) and the 22 items were well targeted to the patients' locations. The ABILHAND measures were strongly related to the ACTIVLIM measures (r=0.76), and poorly related to grip strength (r=0.36 for the right hand and r=0.40 for the left hand). Moreover, the resulting scale can be used for adults and children, allowing manual ability to be assessed from childhood to adulthood.
