Multiple sclerosis and spasticity: the role of anaesthetic nerve blocks on rectus femoris muscle. When should stiff knee be treated with botulinum toxin?

Objective: To compare the effect of rectus femoris diagnostic motor nerve blocks (DNB) with anaesthetics and rectus femoris muscle botulinum toxin (BoNT-A) injection in multiple sclerosis patients with unilateral stiff-knee gait. Design: Prospective observational study Subjects/Patients: Multiple sclerosis patients in stable condition. Methods: Patients underwent evaluation before and 1 hour after the anaesthetic block, and 1 month after the botulinum injection. Assessment included a 10-m walking test, a 6-minute walking test, a timed-up-and-go (TUG) test, and a Baseline Expanded Disability Status Scale (EDSS). Post-DNB and post-BoNT-A satisfaction was measured with the global assessment of efficacy scale. Results: Fourteen patients with unilateral stiff-knee gait due to multiple sclerosis underwent a DNB, among whom 13 received botulinum injections in the rectus femoris muscle after a satisfying test result. Positive post-DNB results correlated with significant functional improvements after BoNT-A. Higher EDSS and longer time from diagnosis correlated with poorer post-DNB and post-BoNT-A absolute outcomes. Conclusion: DNB showed predictive value for BoNT-A outcomes, especially in the case of worse functional status. It effectively predicted endurance and walking speed improvement, while TUG showed greater improvement after botulinum. In cases of uncertain therapeutic benefit, nerve blocks may provide a valuable diagnostic support, particularly in patients with lower functional status. LAY ABSTRACT Multiple sclerosis patients frequently suffer from lower limb spasticity and impaired gait, often associated with severe weakness. A typical finding is the "stiff-knee" gait pattern, due to rectus femoris muscle spasticity. Botulinum toxin is the treatment of choice to reduce spastic hypertonia but may also provide a further reduction in muscle strength with a pharmacological effect lasting up to 6 months. In this study, we assessed the efficacy of anaesthetic nerve blocks in predicting the possible expected effect of botulinum treatment on a shorter period of time (a few hours). Our results showed an interesting correlation between post-block gait functional tests and post-botulinum values, particularly in more compromised patients, suggesting a potential adjuvant role of nerve blocks in guiding the clinical decision.