Objective:
To evaluate the current evidence on the efficacy and safety of BoNT in treating lingual dystonia.

Background: Lingual dystonia is a rare yet debilitating form of dystonia. It is one of the most challenging dystonias to treat as the inappropriate muscle targeting, the unintentional spread of the toxin or a higher than required dose can result in potentially serious side effects.

Method:

A literature search of Medline, Embase, and Cochrane databases was carried out from inception to March 12, 2021. Inclusion criteria: (1) Original prospective studies, randomized controlled or open-label trials or case series. Case reports not included, (2) patients had to be treated for lingual dystonia with BoNT therapy and (3) studies required to provide outcome criteria for efficacy. A total of 154 records were identified. After removing duplicates 142 studies were assessed for eligibility. Full text articles for 33 studies were reviewed. Out of these, eleven studies were included for narrative synthesis.

Results:
All eleven studies (range from 2-172 participants, total N=299) observed improvement in lingual dystonia following BoNT injections in genioglossus with improvement ranging from 37.2% to 100%. There were no randomised controlled trials, three studies were prospective (n=39), the remainder retrospective. The total dose of onabotulinum toxin used ranged from 5U to 60 U, and 10 U to 175 U for abobotulinum toxin. Injections were performed under electromyographic guidance in 8/11 studies. The muscle most commonly injected was the genioglossus. Other muscles injected were intrinsic tongue muscles, hyoglossus, masseter and temporalis. Dysphagia, the most common adverse effect, was seen in 1% to 50% of study participants, necessitating PEG placement in one and causing death in one patient. Other adverse events reported were drooling, speech, chewing and breathing problems needing intensive care management.

Conclusion: There is a lack of randomized controlled trials in the field and significant heterogeneity in the studies including criteria of lingual dystonia subtypes, muscle targeting techniques, doses used, disease duration, concomitant use of other medications, underlying etiologies, and outcome measures. Consensus for diagnostic criteria and outcome measures needs to be established. Guidance with electromyography or ultrasonography might optimize response and minimize complications.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/efficacy-and-safety-of-botulinum-toxin-bont-in-lingual-dystonia/