Objective: –

Background: Functional movement disorders (FMD) are characterized by abnormal movements without an identifiable neurological cause. Diagnosis and management of patients with FMD can be challenging for clinicians [1-3]. Previous studies and case reports have shown that some patients initially diagnosed with FMD are later found to have classical movement disorders, such as Parkinson’s disease or hereditary ataxias [4,5]. THAP1 is a gene cause autosomal dominant dystonia (DYT6), typically presenting with generalized or segmental dystonia involving orofacial muscles [7,8]. SCA8 is an autosomal dominant hereditary ataxia that may also initially mimic functional features [5,6].

Method: A 48-year-old right-handed female presented with a 13-year history of treatment-resistant depression (long-term antidepressants and antipsychotics treatment). Due the psychiatric treatment a severe polyvalent drug allergy appeared. After 11 years of depression she developed involuntary movements in her right hand, which initially resembled a tremor but evolved into a fixed dystonic posture with marked inward rotation. Clinical findings include: a) psychiatric: severe anxiety and depression (HDRS was 31 with suicidal tendencies).; b) neurological: symptoms showed “functional” dystonia, including transient improvement during distraction (e.g., catching a ball with right hand) and voluntary relaxation. Cerebellar signs were absent. Brain MRI was unremarkable. Initially diagnosed with functional dystonia, the patient showed no motor improvement despite psychiatric stabilization. Furthermore, the symptoms progressed to involve the contralateral hand and laryngeal muscles. Whole Exome Sequencing (WES) revealed a likely pathogenic heterozygous mutation in THAP1 (NM_018105.3:c.199dup) and an expansion in SCA8 (ATXN8OS gene, 82 CTG repeats).

Results: Later she tried several Botulinum toxin injections with moderate effects even in high dosage (1000 ED of Dysport). Deep brain stimulation was recommended for the patient.

Conclusion: We report a rare co-occurrence of DYT6 (THAP1) and SCA8 in a patient whose initial clinical presentation strongly suggested a FMD. This case demonstrates importance of long-term follow-up and awareness among movement disorders specialists in patients with FМD [4,5].

References: 1. Park JE. Functional Movement Disorders: Updates and Clinical Overview. J Mov Disord. 2024;17(3):251-261.
2. Dworetzky BA, Baslet G. Functional neurological disorder: Practical management. Neurotherapeutics. 2025 Jul;22(4):e00612. doi: 10.1016/j.neurot.2025.e00612. Epub 2025 May 20. PMID: 40399224; PMCID: PMC12418456.
3. Gilmour, Gabriela S. et al. “The Diagnosis of Functional Movement Disorder Functional movement disorder is diagnosed using positive signs , allowing a clinician to “ rule-in ” the diagnosis.” (2022).
4. Felicio AC, Godeiro-Junior C, Moriyama TS, Shih MC, Hoexter MQ, Borges V, Silva SM, Aguiar Pde C, Andrade LA, Bressan RA, Ferraz HB. Degenerative parkinsonism in patients with psychogenic parkinsonism: A dopamine transporter imaging study. Clin Neurol Neurosurg. 2010 May;112(4):282-5. doi: 10.1016/j.clineuro.2009.12.010. Epub 2010 Jan 12. PMID: 20061077.
5. S. Jimsheleishvili, D. Crandon, J. Margolesky. Case Report Functional Neurological Disorder as a Harbinger of Spinocerebellar Ataxia 8 [abstract]. Mov Disord. 2024; 39 (suppl 1). https://www.mdsabstracts.org/abstract/case-report-functional-neurological-disorder-as-a-harbinger-of-spinocerebellar-ataxia-8/. Accessed March 14, 2026.
6. Cleary JD, Subramony SH, Ranum LPW. Spinocerebellar Ataxia Type 8. 2001 Nov 27 [Updated 2021 Apr 22]. In: Adam MP, Bick S, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2026. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1268/
7. Myrzayev Zh, Shashkin Ch, Bagautdinov D, Houlden H, Kaiyrzhanov R. Distoniya DYT6 s tardivnoy khoreey i otlichnym rezul’tatom lecheniyal glubokoy stimulyatsiey mozga v oblasti medial’noy chasti blednogo shara [DYT-6 dystonia with drug induced chorea and an excellent response to GPi deep brain stimulation], Vestnik Avitsenny [Avicenna Bulletin], 2022;24(3):413-20.Available from: https://doi.org/10.25005/2074-0581-2022-24-3-413-420
8. Blanchard A, Ea V, Roubertie A, Martin M, Coquart C, Claustres M, Béroud C, Collod-Béroud G. DYT6 dystonia: review of the literature and creation of the UMD Locus-Specific Database (LSDB) for mutations in the THAP1 gene. Hum Mutat. 2011 Nov;32(11):1213-24. doi: 10.1002/humu.21564. Epub 2011 Sep 15. PMID: 21793105.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/late-onset-thap-1-with-sca8-expansion-mimicking-functional-movement-disorder-case-report/