INCAT disability score: a critical analysis of its measurement properties

Abstract

Background: The INCAT (Inflammatory Neuropathy Cause and Treatment) disability score is a measure of activity limitation. It is used frequently as a primary endpoint in inflammatory polyneuropathy clinical trials. A comprehensive critical analysis of its measurement properties has not been performed.

Methods: Critical analysis of measurement properties.

Results: The INCAT disability score was derived based on items from Guy's Neurological Disability Scale (GNDS), a disability measure intended for application in multiple sclerosis. Strengths of the INCAT score include evaluation of upper and lower limb dysfunction, ease of administration (feasibility), high face validity, and high reliability. Weaknesses of the scale include concerns about methodological quality of validation studies; failure to properly capture activity limitations due to proximal arm weakness, or fatigue; heavy individual item weighting; and poor sensitivity for detection of clinically important change.

Conclusions: Although the INCAT scale has been an effective tool in inflammatory polyneuropathy studies, its limitations may warrant development of new scales.

Keywords: CIDP; chronic inflammatory demyelinating polyneuropathy; interpretability; measurement; peripheral neuropathy; reliability; responsiveness; validity.