Case report: Lingual dystonia symptoms treated with botulinum toxin in patients with THAP1 mutation

Background: THAP1 mutation dystonia is a known genetic cause of generalized dystonia. THAP1 mutation frequently presents with clinical features of bulbar dysfunction, including oromandibular and lingual dystonia. Patients complain of significant speech, chewing, and swallowing difficulties leading to major occupational and social disabilities. While bilateral globus pallidus internus deep brain stimulation (DBS) is powerful therapy for generalized dystonia and improves dystonia symptoms in the cervical and limb region, it may not improve speech despite multiple adjustments to the stimulation parameters. Treating lingual dystonia symptoms with oral medications is commonly unsatisfactory. Botulinum toxin injection, a potent therapy for focal forms of dystonia is currently underutilized in clinical practice for treating lingual dystonia.Cases: We present two patients with THAP1 mutation reporting lingual dystonia symptoms. The first patient did not meet the eligibility criteria for DBS therapy due to significant psychiatric symptoms. The second patient received DBS with improvements in cervical, limb, and trunk symptoms but complained of severe speech difficulties that did not improve despite multiple programming sessions. These patients were treated with botulinum toxin injections every 12 weeks for more than 3 years, with speech improvements lasting most of the cycle. For the most part they tolerated botulinum toxin without bothersome side effects. Along with the clinical histories, we present objective perceptual analysis of speech samples collected before and after botulinum toxin injections in one of the treatment cycles.Conclusion: Botulinum toxin injections that are clinically beneficial for mitigating lingual dystonia symptoms should be utilized to address symptoms of THAP1 mutation dystonia that may not be amenable to other therapies, such as the DBS.