Norfolk QOL-DN: validation of a patient reported outcome measure in transthyretin familial amyloid polyneuropathy

Abstract

The Norfolk Quality of Life-Diabetic Neuropathy (QOL-DN) questionnaire is an instrument to assess QOL in diabetic polyneuropathy. The objective of this observational, cross-sectional study in 61 patients with V30M transthyretin familial amyloid polyneuropathy (TTR-FAP) and 16 healthy volunteers was to validate the Norfolk QOL-DN for assessment of QOL in TTR-FAP. Comparisons were conducted to identify the best items to discriminate disease stages and assess which individual Norfolk domains (symptoms, large fiber, small fiber, autonomic, and activities of daily living) would be most affected by disease stage. Analysis of individual items revealed a significant pattern of discrimination among disease stages (p < 0.001). Total QOL scores increased (indicating worsening) with duration of symptoms, with a steeper increase observed earlier in the course of disease. Significant correlations were observed between each Norfolk domain and other measures of neurological function. Limitations include cross-sectional study design, low patient numbers in this rare disease, and the ordinal-based character of the metric used; future areas to explore include item response theory approaches such as Rasch analysis. These results suggest the Norfolk QOL-DN is a reliable indicator of the impact of disease severity on QOL in patients with TTR-FAP.

Keywords: Norfolk quality of life; nerve-fiber function; neurological function; outcome measure; transthyretin amyloid polyneuropathy.