The minimal clinically important change in the motor section of the Burke-Fahn-Marsden Dystonia Rating Scale for generalized dystonia: Results from deep brain stimulation.

BACKGROUND: The minimal clinically important difference (MCID) describes the smallest change in an outcome that is considered clinically meaningful. The Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) is the most frequently rating scale assessing the efficacy of deep brain stimulation therapy (DBS) for dystonia. To expand our understanding, we evaluated the MCID thresholds for the BFMDRS motor subscale (MS) using physician-reported outcomes. METHODS: We assessed the MCID thresholds for the BFMDRS using movement disorder specialist ratings of videotapes from patients with genetically determined dystonia (Tor1A and THAP1) who underwent bilateral globus pallidum internum (GPi) DBS. We calculated the effect size of the BFMDRS-MS change and determined the MCID thresholds using the Clinical Global Impression of Change (CGIC). RESULTS: Twelve participants with a median age at DBS of 44.5 (range:27-68) had baseline and follow-up BFMDRS-MS with a median post-DBS follow-up of 5.5 years. Based on descriptive analysis, patients with good improvement after DBS according to the CGIC [8/12 (67%)] had a median BFMDRS-MS score reduction of 77% [Interquartile range (IQR):66.2;91.0) with an effect size of 0.39, and those with non-improvement [4/12 (33%)], had a median BFMDRS-MS score reduction of 62% (IQR:36.6;83.6). CONCLUSIONS: Our MCID estimates can be utilized in clinical practice in judging clinical relevance. However, further larger, powered studies are needed to simultaneously determine and compare MCID using patient and physician-reported outcomes in segmental and generalized dystonia in genetic and non-genetic populations.

Digitized spiral analysis may be a potential biomarker for brachial dystonia.

INTRODUCTION: Objective measures for detection and quantification of dystonic movements may guide both diagnosis and clinical monitoring. Digitized spiral analysis is a non-invasive method used to assess upper limb motor control in movement disorders and may have utility in dystonia. We aimed to determine if digitized spiral analysis can distinguish dystonia subjects from controls, and evaluated correlation with a validated clinical rating scale. METHODS: Kinematic, dynamic, and spatial attributes of Archimedean spirals drawn with an inking pen on a digitizing tablet were compared for participants with brachial dystonia and either Tor1A (DYT1) (n = 15) or THAP1 (DYT6) mutations (n = 12) and age and gender matched controls (n = 27) using Receiver Operator Characteristics (ROC) analysis. Spiral indices including an overall degree of severity (DoS) were also calculated and correlated with clinical severity ratings as measured by the Burke-Fahn-Marsden scale. RESULTS: Dystonia spirals had significantly higher severity scores as well as higher measures of spiral irregularity compared to controls. ROC analysis demonstrated that the DoS score had good discriminative ability to distinguish dystonia spirals from controls, with an Area Under the Curve (AUC) of 0.87. Measures of spiral irregularity correlated with validated clinical rates of dystonia severity in the analyzed arm, with one particular index, Residue of Theta vs R, showing the highest correlation (r = 0.55, p = 0.005). CONCLUSION: Digitized spiral analysis may be a promising non-invasive method to objectively quantify brachial dystonia. It may also be a useful way to monitor subtle changes in dystonia severity over time not captured with current clinical rating scales.