Longitudinal Clinical and Pallidal LFP Assessment in a Paediatric Patient With Myoclonus–Dystonia Associated With ANO3 Mutation: A Long-Term Follow-Up Case Study

Background Myoclonus–dystonia is a clinically and genetically heterogeneous movement disorder characterized by proximal myoclonic jerks, frequently accompanied by dystonia. Although ANO3-related cases are less common than SGCE-associated forms, previous reports describe favourable responses to GPi deep-brain stimulation (DBS). Sensing-enabled neurostimulators allow chronic acquisition of local field potentials (LFPs) from the globus pallidus internus (GPi), offering unique opportunities to study network reorganization under neuromodulation. Here, we describe the long-term clinical and neurophysiological evolution of a paediatric patient with genetically confirmed ANO3-related myoclonus–dystonia treated with GPi-DBS. Case description A 14-year-old boy developed symptoms at age 9, presenting with lower-limb jerks during gait and right-arm jerks during writing, along with mild dystonic dysarthria, dystonic posturing, distal myoclonus, and bilateral lower-limb dystonia causing gait impairment. Genetic testing identified a maternally inherited ANO3 missense variant (c.1391C>T; p.Thr464Ile, ACMG class 3). Pharmacological treatments (L-dopa, trihexyphenidyl) yielded minimal benefit; consequently, multidisciplinary evaluation supported candidacy for bilateral GPi-DBS. Methods Clinical assessments were conducted preoperatively and during follow-up using the Burke–Fahn–Marsden Dystonia Rating Scale–Motor (BFMDRS-M) and the Unified Myoclonus Rating Scale (UMRS). Local field potentials (LFPs) were recorded via the Percept™ PC device during standardized resting-state conditions (eyes-open and eyes-closed). Three-minute LFP signals were acquired from bipolar contact pair 1–2; this pair was selected based on the postoperative localization within the GPi, confirmed via Lead-DBS MATLAB toolbox. Signals were band- pass filtered (1–48 Hz) and power spectral density (PSD) was computed using Welch’s method. Absolute and relative power were calculated for canonical frequency bands: delta (1–3 Hz), theta (3–7 Hz), alpha (7–12 Hz), low beta (12–20 Hz), high beta (20–30 Hz), low gamma (30–45 Hz). Longitudinal changes in oscillatory activity were analysed per hemisphere and condition, and compared with clinical trajectories. Results Clinical evaluations demonstrated improvement in dystonia and myoclonus compared with baseline, with enhanced gait stability and functional performance. LFP analysis revealed time-dependent modulation of GPi oscillatory activity, with persistent predominance of low-frequency components across sessions. The right GPi demonstrated a progressive increase in delta-band activity, whereas theta, alpha, and beta bands showed relative decreases over time. The left GPi displayed a more stable spectral profile with only modest fluctuations. These patterns were consistent across eyes-open and eyes-closed conditions and qualitatively aligned with the clinical evolution. Conclusions This case contributes to the characterization of longitudinal GPi-LFP dynamics in paediatric ANO3-related myoclonus–dystonia treated with DBS. Clinical improvement was paralleled by progressive modulation of pallidal oscillations, supporting the concept of dynamic network reorganization under neuromodulation. Although limited to a single patient, the correspondence between symptom reduction and LFP changes highlights the relevance of chronic sensing approaches for optimizing and personalizing DBS strategies in paediatric movement disorders.