describe the safety and utility of botulinum toxin in mitigating muscle spasms/rigidity in Stiff Person Syndrome (SPS).

SPS is a rare, chronic and disabling disorder that causes marked muscle spasms, stiffness, and rigidity. Persons suffering from SPS may have a varied presentation but, most notably, chronic and disabling muscular spasms which cause significant disability. Pharmacotherapies are often poorly tolerated due to sedation and cognitive impairment. Hence, there is a great unmet need for therapies that not only can help minimize the symptoms of SPS, but also have less potential systemic side effects. Botulinum Toxin, an under-investigated and infrequently used treatment modality, may directly improve muscle spasm and rigidity, thereby improving quality of life.

This observational study included 20 patients with SPS who were longitudinally treated at Johns Hopkins Hospital from 2011-2018. Onabotulinum toxin doses ranged from 100 up to 800 units. Treatment response was determined following injections by patient report; reduction in pain and/or frequency and severity of spasms. We categorized responses qualitatively by poor, moderate and robust response. Side effects were also obtained.

Amongst the 20 patients, majority were female (85%).  Our cohort had varied injection sites, including paraspinals 35%, lower extremity 40%, cervical 10%, hand 5%, and abdominal muscles 5%. Robust response was reported in 30% (6/20), 25% (5/20) reported moderate response, and 40% (8/20) reported poor response amongst which 25% (2/8) had an initial moderate response which abated. Although not consistently recorded, around 25% of our patients were able to decrease their oral medication burden. Among the responders 80% continued with injections.

In our study, 55% of patients had a positive response to onabotulinum toxin with subjective improvement in spasms and/or pain along with improvement in quality of life.  Future studies will be needed to objectively demonstrate the effect of botulinum toxin in SPS.