Objective: We report the case of a man affected by FXTAS, presenting with disabling tremor who experienced a significant and long-lasting benefit from botulinum neurotoxin (BoNT) injection treatment.

Background: Fragile X-associated tremor/ataxia syndrome (FXTAS) is a X-linked neurodegenerative disease due to the CGG trinucleotide expansion in the premutation range (50-200 triplets) in the FMR1 gene [1]. It manifests as late-onset ataxia associated with postural-kinetic tremor and cognitive decline. Tremor may represent a disabling symptom in this condition; however, the most common treatment approaches are often unsatisfying due to lack of efficacy or side effects.

Method: A 59-year-old man came to our attention for a 10-years-lasting hand tremor. The tremor, mainly during voluntary movements, began in the right hand and progressively extended to the left hand and the lower limbs. The neurological examination revealed a moderate, right-prevailing, kinetic tremor of the hands, accompanied by rest and postural components, with subtle right-hand clumsiness. The brain MRI showed a cerebello-pontine atrophy with T2-FLAIR hyperintensity of both the middle cerebellar peduncles [figure1] and the splenium of corpus callosum. Genetic testing was performed and revealed an expansion of the CGG-trinucleotide FMR1 gene sequence with 106 triplets.

The patient did not tolerate oral propranolol therapy due to bradycardia. Hence, an attempt with BoNT was made with a single session of incobotulinum toxin type A injection (diluted in 2cc of 0.9% sodium chloride solution) in the right flexor digitorum superficialis muscle (30 units) and right extensor digitorum muscle (10 units).

A pre-injection and post-injection evaluations with wrist-worn accelerometry were performed by using a wrist triaxial accelerometer and recording tremor in rest, postural and kinetic conditions.

Results: About two weeks after the injection, the patient reported a subjectively significant reduction of the tremor. The post-injection accelerometric assessment demonstrated a great decrease in the amplitude of the tremor [figure2]. The beneficial effect lasted about 5 months.

Conclusion: BoNT injection typically constitutes a therapeutic second-line-option in tremor syndromes refractory to pharmacological agents [2-3]. Our case suggests the possibility of its broader application in the symptomatic treatment of FXTAS-related tremor.

References: [1] Hagerman P. Fragile X-associated tremor/ataxia syndrome (FXTAS): pathology and mechanisms. Acta Neuropathol. 2013;126(1):1-19. doi:10.1007/s00401-013-1138-1
[2] Mittal SO, Lenka A, Jankovic J. Botulinum toxin for the treatment of tremor. Parkinsonism Relat Disord. 2019;63:31-41. doi:10.1016/j.parkreldis.2019.01.023
[3] Mittal SO, Pandey S. Botulinum toxin for the treatment of tremor. J Neurol Sci. 2022;435:120203. doi:10.1016/j.jns.2022.120203

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MDS Abstracts - https://www.mdsabstracts.org/abstract/botulinum-neurotoxin-in-fxtas-related-tremor-a-successful-case-report/