Objective: Validated, reliable instruments to assess spasticity-related arm pain are not available. Non-specific pain-assessment scales have not been validated in this condition either and may be unsuitable for nursing-home patients. Without such validated scales, the effects of botulinum toxin on this condition cannot be investigated in a scientifically robust manner. The objective of this study was to evaluate the internal consistency, reliability, and validity of the Spasticity-Associated Arm Pain Scale (SAAPS) for adults with post-stroke upper-limb spasticity, and its sensitivity for detecting pain reduction following incobotulinumtoxinA treatment.
Methods: Psychometric evaluation of a five-item pain-assessment tool was conducted in this prospective, multicenter, open-label, observational study, involving adults with post-stroke upper-limb spasticity (inter-rater reliability, n=25; all other measures, n=61). Internal consistency was analyzed using Cronbach’s alpha coefficients. Test-retest reliability was assessed using intraclass correlations, Spearman’s rho, polychoric correlation, and Kendall’s Tau-b coefficients. Inter-rater reliability was assessed using weighted kappa. SAAPS validity was assessed using correlations with patient/investigator ratings on an 11-point numerical rating scale. Sensitivity of SAAPS was investigated 4-6 weeks after an incobotulinumtoxinA injection.
Results: Test-retest reliability was high (all measured coefficients >0.70) and weighted kappa for inter-rater reliability (0.45-0.69) indicated good/fair agreement. SAAPS scores were reduced by 3.7 points (mean) 4-6 weeks post-treatment (p<0.0001), and indicated pain reduction in 79.7% of patients. SAAPS scores and numerical rating scale pain ratings were significantly correlated (p<0.001).
Conclusion: SAAPS is a reliable, valid tool for assessing pain reduction after incobotulinumtoxin A treatment in adults with post-stroke upper-limb spasticity.