Objective: To report clinical trajectory and functional improvement of a child with atypical KMT2B-related dystonia following bilateral GPi-DBS performed at a moderate disease stage.

Background: KMT2B-related dystonia is a major genetic cause of progressive childhood-onset dystonia, typically beginning in a lower limb and progressing to generalized dystonia involving cranial, cervical, and laryngeal regions. Patients may also present with dysmorphism, short stature, intellectual disability, ocular motor abnormalities, and psychiatric comorbidities. Atypical presentations, including upper limb or oromandibular onset, are less common. DBS is an established treatment for severe, medically refractory dystonia, with 30–40% symptom improvement; earlier DBS in genetic dystonias may yield better functional outcomes.

Method: We report the longitudinal clinical, imaging, genetic, and therapeutic course of a patient with atypical KMT2B-related dystonia, diagnosed at age 12. Motor severity was assessed using the Burke–Fahn–Marsden Dystonia Rating Scale–Motor (BFMDRS-M). Pharmacological treatments and multidisciplinary interventions were documented. GPi-DBS was approved by a multidisciplinary team.

Results: Symptoms began at age 8 with right-hand dystonia during writing in a patient with ADHD and dysphasia. Dystonia progressed to the left upper limb by age 11 with abnormal posturing of the arm and compensatory shoulder elevation. By age 12, dysarthria, divergent strabismus, left lower-limb involvement, and signs of precocious puberty emerged. Genetic testing identified a de novo heterozygous KMT2B variant, confirming a KMT2B-related dystonia. Levodopa/carbidopa and trihexyphenidyl provided minimal benefit. The BFMDRS-M scores worsened from mild (BFMDRS-M: 16) at diagnosis to moderate (BFMDRS-M: 39) within 10 months. Bilateral GPi-DBS was performed at age 13, resulting in functional improvement. BFMDRS-M score improved from 31 preoperatively to 6 at 3-month follow-up, representing an 80% reduction.

Conclusion: This case suggests that early bilateral GPi-DBS performed at a moderate stage may provide meaningful motor and functional improvement in medically refractory KMT2B dystonia in children.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/functional-improvement-following-early-gpi-dbs-for-moderate-stage-atypical-kmt2b-dystonia-a-case-report-in-a-13-year-old-girl/