Clinimetric evaluation of a new overall disability scale in immune mediated polyneuropathies

OBJECTIVES: To determine the validity, reliability, and responsiveness of a new overall disability sum score in immune mediated polyneuropathies. METHODS: Three impairment measures (MRC sum score, sensory sum score, grip strength (Vigorimeter)) and three disability scales (an overall disability sum score (ODSS), Hughes' functional scale (f score), Rankin scale) were assessed in a cross sectional group of 113 clinically stable patients (83 with Guillain-Barre syndrome, 22 with chronic inflammatory demyelinating polyneuropathy (CIDP), eight with a gammopathy related polyneuropathy). The ODSS was also used serially in 20 patients with recently diagnosed Guillain-Barre syndrome (n = 7) or CIDP (n = 13) and changing clinical conditions. Multiple regression studies were performed to compare the impact of impairment disturbances (independent variables) on the various disability scales (dependent variable). RESULTS: Moderate to good construct validity (stable group: Spearman's rank test (absolute values), r = 0.41-0.79; longitudinal group: multiple correlation coefficient, R = 0.69-0.89; p < 0.006 for all associations) and reliability (intraclass correlation coefficient, R = 0.90-0.95; p < 0.0001) were demonstrated for the ODSS. Its SRM values were high (> 0.8), indicating good responsiveness. Impairment measures accounted for a higher variance proportion of the ODSS compared with the f score and Rankin (R = 0.64 v 0.56 and 0.45, respectively). CONCLUSIONS: All clinimetric requirements were met by the overall (arm and leg) disability sum score in immune mediated polyneuropathies. Its use is therefore suggested in evaluating immune mediated polyneuropathies.