Botulinum toxin as a potential adjunct therapy in stiff person syndrome spectrum disorders.

[BACKGROUND] Stiff person syndrome spectrum disorders (SPSD) are a disabling group of immune-mediated disorders that most commonly cause progressive rigidity and painful spasms. Botulinum neurotoxin (BoNT) has anecdotally improved SPSD symptoms, though evidence regarding treatment strategy and clinical efficacy is scarce.

[OBJECTIVES] To characterize the location, frequency, dosage, and clinical response to BoNT injections in patients with SPSD.

[DESIGN] We conducted a retrospective observational cohort study.

[METHODS] SPSD patients who received BoNT treatments between August 2018 and February 2024 were included. Detailed information about the injections (formulation, dose, muscle), subjective patient-reported response, and concurrent therapies was recorded and compared between the first, third, and eighth BoNT visits.

[RESULTS] Thirty-seven SPSD patients were included. The majority had classic SPS (83.8%), were female (67.7%), white (78.4%), and on immune therapies (70.3%). The paraspinal muscles, hip flexors, distal leg flexors, and shoulder girdle muscles were most frequently injected. Supramaximal total doses up to 980 units of BoNT were used safely. The most common side effect was transient worsening of pain/spasms, which resolved with peak dose effect. Subjective clinical response was positive, with a median patient-reported 5-point Likert rating of 4, 5, and 5 after visits 1, 3, and 8.

[CONCLUSION] BoNT may be an effective and durable adjunctive symptomatic therapy for people with SPSD with targeted muscle selection based on specific symptomatology. Injections into multiple body regions and use of supramaximal dosages may be required for adequate symptom control in this patient population. As our data lacked objective measures and relied on semiqualitative self-reported patient responses, conclusions about the utility of BoNT are limited and randomized placebo-controlled trials are needed to evaluate the impact of BoNT on improving quality of life, mobility, and burden of systemic symptomatic treatment.