Generic scale compares manual ability across diagnoses

By Lucy Piper, Senior medwireNews Reporter

Researchers have developed a generic manual ability scale unbiased by diagnosis that could allow quantitative comparisons of manual ability between diagnostic groups.

They explain that, although disease-specific instruments are more discriminative for detecting and quantifying clinically significant health changes, a generic scale "allows the manual ability of patients with different diagnoses to be compared."

It could therefore be used, for example, "to identify the relative burden of diagnoses, compare various healthcare programmes and demonstrate evidence of cost-effectiveness of different healthcare interventions," Carlyne Arnould (Haute Ecole Louvain en Hainaut, Montigines-sur-Sambre, Belgium) and colleagues say.

The team analyzed prior data from cross-sectional studies on 83 manual activities that had been identified in the development of disease-specific ABILHAND manual ability questionnaires.

They then assessed these activities to investigate the co-calibration of patient-perceived difficulty in carrying out these activities on a generic scale.

The disorders studied were chronic stroke (103 adults), cerebral palsy (113 children), rheumatoid arthritis (112 adults), systemic sclerosis (156 adults), and neuromuscular disorders (124 children and 124 adults).

The researchers refined the manual activities to 11 items sharing a common location among the diagnostic groups and 41 items having a location specific to asymmetric or symmetric disorders.

The resulting ABILHAND generic scale showed that children with cerebral palsy and neuromuscular disorders have significantly less manual ability than patients with rheumatoid arthritis, who, in turn, have significantly less manual ability than adults with chronic stroke, systemic sclerosis, and neuromuscular disorders.

Arnould et al found that the difficulties of most manual activities were diagnosis dependent.

The vast majority (85%) of variance in difficulties carrying out manual activities was due to the symmetric or asymmetric nature of the disorder (57% of item difficulty variance) and the proximal or distal nature of the disorder (28% of variance).

For example, activities requiring greater bimanual involvement, such as "peeling potatoes with a knife," tended to be rated as more difficult by patients with asymmetric disorders than by patients with more symmetric disorders, the researchers report.

"On the other hand, unimanual activities (eg, 'turning on a television')… were rated as less difficult for patients with asymmetric disorders, probably because these activities can be achieved by exclusively using the unaffected or less affected hand," they add in BMJ Open.

The researchers conclude that the fact that most of the difficulty in doing manual activities was diagnosis-dependent "emphasizes the danger of using generic scales without prior investigation of item invariance across diagnostic groups."

Nevertheless, they add that "using 11 linked items unbiased by diagnosis, we successfully constructed, from a metric point of view, a unidimensional scale common to six diagnostic groups by separating items with difficulties specific to asymmetric and symmetric disorders."

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