Side Benefit of Botulinum Toxin A? Reduced IOP in Hemifacial Spasm

— Patients with hemifacial spasm and glaucoma need eye follow-up after injection

by
Diana Swift, Contributing Writer, MedPage Today
October 29, 2023

Injection with botulinum toxin A (BTX-A) for hemifacial spasm (HFS) may have an additional benefit: decreasing unilateral eyelid spasms and intraocular pressure (IOP), according to a small Brazilian study.

Mean IOP was 11 ± 3.42 mm Hg before treatment in the affected eye and 9 ± 2.98 mm Hg in the contralateral eye (P=0.012). Post-BTX-A injection, however, no interocular difference was detected using the digital transpalpebral tonometer Diaton (P=0.204) or the Goldmann applanation tonometer (GAT; P=0.971), reported Sebastião Cronemberger, MD, of the Federal University of Minas Gerais in Belo Horizonte, Brazil, and colleagues.

The study is the first to use Diaton to gauge the effect of blepharospasm on IOP before and after BTX-A treatment, they wrote in International Ophthalmology.

Involuntary blepharospasm is thought to be associated with elevated IOP, the sole modifiable risk factor for glaucoma, the authors noted. “Therefore, HFS patients suspected to have or diagnosed with glaucoma should continue to be followed periodically with an adequate workup after treatment with BTX-A.”

Commenting on the study, Drew Carey, MD, of the Wilmer Eye Institute at Johns Hopkins Medicine in Baltimore, said it’s not clear whether HFS per se causes artificially high IOP. “But it’s long been known that people who squeeze their eyes for various reasons can have an artificially higher pressure when we measure during screening for glaucoma.”

He cautioned, however, that in many cases ostensible IOP elevation may be an artifact of the measurement mode.

As to a takeaway message regarding ophthalmological treatment, he noted that “this study would not have major clinical implications because most HFS patients would get Botox injections anyway.”

So while the results do not support an immediate strategy to treat other causes of IOP with neurotoxin, “they might raise awareness in people who are not being treated optimally for HFS that they should take possible elevation of IOP into account when they are being screened for glaucoma,” he said.

While confirming that injection decreases IOP and improves patients’ quality of life, Cronemberger’s group noted several issues that need addressing. “If these patients were not treated with BTX-A, would they develop glaucoma, or would there be a decrease in IOP between contractions secondary to increased aqueous drainage caused by the spasms?”

Further studies are necessary to answer these questions, they said.

For this single-center study, measurements were taken in 27 patients with moderate-to-severe HFS both before and after BTX-A, the first-line treatment for HFS, from October 2017 to April 2019. Mean age was 59.8 years, and 63% were women. The right side was affected by HFS in 16 patients, and the duration of the symptoms ranged from 1 to 21 years, with an average of 10 years. Patients with ocular hypertension or glaucoma were excluded.

Participants received a complete ophthalmological assessment 10 to 20 days post-treatment, when IOP was also measured by GAT (which can be compromised by eyelid spasms) and then compared with the Diaton results. Participants were also screened for glaucoma with automated perimetry, optical coherence tomography, and pachymetry.

Study limitations included the small population due to the rarity of HFS, the short-term follow-up, and the fact that IOP was not measured by GAT before injection.