Reliability of functional outcome measures in adults with neurofibromatosis 1

To determine intra-rater and inter-rater reliability of functional outcome measures in adults with neurofibromatosis 1 and to ascertain how closely objective and subjective measures align.

A total of 49 ambulant adults with neurofibromatosis 1 aged 16 years and over were included in this observational study: median age 31 years (range: 16-66 years), 29 females, 20 males. Participants were video-recorded or photographed performing four functional outcome measures. Four raters from the neurofibromatosis centre multi-disciplinary team independently scored the measures to determine inter-rater reliability. One rater scored the measures a second time on a separate occasion to determine intra-rater reliability. The measures evaluated were the functional reach, timed up and go, 10 m walk and a modified nine-hole peg tests. Participants also completed a disease-specific quality-of-life questionnaire.

Inter-rater reliability and intra-rater reliability scores (intra-class coefficient) were similar for each outcome measure. Excellent rater agreement (intra-class coefficient, r ⩾ 0.9) was found for the functional reach, timed up and go and the 10 m walk tests. Rater agreement was good for the modified nine-hole peg test: intra-class coefficient r = 0.75 for intra-rater reliability and 0.76 for inter-rater reliability. The timed up and go and the 10 m walk tests correlated highly with perceived mobility challenges in the quality-of-life questionnaire.

The functional reach, timed up and go and 10 m walk tests are potentially useful outcome measures for monitoring neurofibromatosis 1 treatment and will be assessed in multi-centre and longitudinal studies.