The cross-cultural adaptation and psychometric validation of the MSSS-88 for use in Italian patients with multiple sclerosis

Evaluation of the Multiple Sclerosis Spasticity Scale 88: A Short Report

Background:

The Multiple Sclerosis Spasticity Scale 88 (MSSS-88) is designed to capture the patient experience and impact of spasticity, but there is limited evaluation against clinician-rated measures of spasticity.

Objective:

To evaluate the convergent validity and responsiveness of the MSSS-88.

Design:

Longitudinal study.

Setting:

University Laboratory.

Subjects:

Thirty-four people with multiple sclerosis.

Methods:

People with multiple sclerosis (MS; n = 34) completed the self-reported 12-item Multiple Sclerosis Walking Scale, Multiple Sclerosis Spasticity Scale, Barthel Index alongside the clinician-rated Ashworth Scale, and a laboratory-based measure of ankle spasticity. Spasticity measure responsiveness was evaluated in 20 participants at two time points, an average of 8.75 ± 3.8 months apart.

Results:

In people with MS (mean age 55.1 ± 8.1 years; Expanded Disability Scale range 4.5-7.0), spasticity symptom specific subscales of the MSSS-88 (stiffness and spasms) showed strong and significant correlations with the clinician-rated Ashworth Scale (r = 0.52-0.53; P < .01). Responsiveness of the MSSS-88 was comparable to a laboratory-based measure of ankle spasticity.

Conclusions:

Our findings lend additional support to the convergent validity of this measure.

The 88-item Multiple Sclerosis Spasticity Scale: a Rasch validation of the Italian version and suggestions for refinement of the original scale

BACKGROUND

In multiple sclerosis (MS), the impact of spasticity on the patient's life is a key issue, and it is fundamental that existing tools measuring the patient's perspective undergo psychometric analysis and refinement to optimize confidence in their use in clinical practice and research.

OBJECTIVE

We examined-by Rasch analysis (RA)-the main metric characteristics of the 88-item Multiple Sclerosis Spasticity Scale (MSSS-88) to: (i) further validate its Italian version (MSSS-88-IT), previously validated through classical test theory methods only and (ii) independently verify the measurement properties of the original scale.

METHODS

MSSS-88 data from a convenience sample of 232 subjects with MS underwent RA, mainly examining item fit, reliability indices, test information function, dimensionality, local item independence, and differential item functioning (DIF).

RESULTS

Most items fitted the Rasch model, but 13/88 items showed a misfit in infit and/or outfit values. Rasch reliability indices were high (> 0.80). Test information functions in most subscales showed a sharp decrease in measurement precision as the ability level departs from the quite limited central range of maximal information. The unidimensionality of each subscale was confirmed. Thirteen item pairs showed local dependency (residual correlations > 0.30) and three items presented DIF.

CONCLUSION

Reliability, dimensionality and some internal construct validity characteristics of the MSSS-88-IT were confirmed. But, drawbacks of the original MSSS-88 emerged related to some item misfit, redundancy, or malfunctioning. Thus, further large independent studies are recommended, to verify the robustness of previous findings and examine the appropriateness of a few targeted item replacements.