Objective: To analyze clinical characteristics of writing dystonia in a pediatric cohort, and test clinical efficacy of globus pallidus internus (GPi) chronic deep brain stimulation (DBS) using an adapted version of the Writer’s Cramp Rating Scale (WCRS).

Background: Action dystonia during writing is a common manifestation of children with different forms of dystonia. It may interfere with the acquisition of reading and writing abilities. Pediatric writing dystonia differs in various aspects from an idiopathic writer’s cramp, involving upper limb proximal muscles. The WCRS+S (adding shoulders score) has been recently adapted by our group, rating the severity of writing dystonia in children with epsilon-sarcoglycan related myoclonic dystonia with good results.

Method: We conducted a longitudinal prospective study, selecting patients over 5 years old, with writing dystonia of variable etiology, who had handwriting abilities before receiving GPi-DBS at our institution (n=16). Writer’s cramp at baseline and after GPi-DBS was analyzed using WCRS+S (0 [no impairment]-32) and BFM scales. Each examination was filmed following a standardized protocol, evaluated by two movement disorders pediatric neurologists.  Wilcoxon signed rank test was used to compare pre and post-DBS scale scores.

Results: Sixteen patients with segmental/generalized dystonia who had writing dystonia underwent DBS surgery at a mean age of 12.37 (range=7-19 y.o; 10 females, 6 males). We analyzed clinical outcome of writing dystonia, classifying patients into three dystonia phenotypes: isolated (n=7; etiology was TOR1A, KMT2B, IMPDH2 and idiopathic), combined myoclonus-dystonia (n=6, SGCE) and complex (n=3, GNAO1, GCDH and GM type 3). 

In the 16 patients, the WCRS+S total score median at baseline was 16 (q1-q3: 14-18.5),  improving on follow-up post-DBS to 6 (q1-q3: 3.75-12), p=0.0007. BFM scores also showed significant improvement (p=0.008). WCRS+S outcomes showed a poor correlation when compared to BFM outcomes. Due to the low number of patients, no differences could be established between dystonia groups.

Conclusion: Writing dystonia in children can be successfully treated by GPI-DPS. The WCRS+S is a useful tool to correctly evaluate writing dystonia in pediatric patients of different etiologies, and helps quantify symptom relief in patients that have undergone DBS.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/writing-dystonia-in-children-improves-after-chronic-stimulation-of-globus-pallidus-internus/