# Geometric Microstructural Characteristics of White Matter Differentiate Patients With Facial Dyskinesias and Palsy

## TL;DR

This study shows that white matter geometry and integrity in the brain can help distinguish between different facial movement disorders.

## Contribution

The study introduces geometric metrics from Director Field Analysis to better differentiate facial dyskinesias and palsy.

## Key findings

- Geometric metrics and FA/MD were altered in FP and HFS patients compared to healthy controls.
- MS patients showed significant changes only in DFA metrics.
- Combining FA/MD with DFA metrics improved diagnostic differentiation between FP/HFS and MS.

## Abstract

The heterogeneous and homogeneous clinical manifestations of peripheral facial palsy (FP), hemifacial spasm (HFS), and Meige's syndrome (MS) complicate the differentiation of diagnoses for these facial motor diseases. To comprehensively investigate the white matter microstructural characteristics in patients with facial dyskinesias and palsy using geometric and integrity metrics in DTI.

In this prospective study conducted from September 2020 to January 2022, patients with FP, HFS, and MS, as well as sex‐matched healthy control subjects, underwent 3.0 T MRI. Geometric metrics (i.e., splay, bend, twist, and total distortion) based on “Director Field Analysis” and fractional anisotropy (FA) and mean diffusivity (MD) were calculated from DTI data. Cross‐sectional tract‐based spatial statistics were performed among FP, HFS, MS patients, and healthy controls. The correlation between disease severity and DTI metrics was evaluated. Additionally, the geometric microstructural properties combining FA and MD were used to classify FP, HFS, and MS patients using machine learning methods.

Geometric metrics and FA/MD were widely altered across white matter in FP and HFS patients compared with healthy controls. However, in MS patients only DFA metrics were significantly altered. FA and DFA values strongly correlated with the severity of facial movement disorder in FP patients. Combing conventional FA/MD value with DFA metrics enabled the diagnostic differentiation of FP and HFS from MS.

Our findings demonstrated that the geometric microstructural information of white matter fibers could provide novel insight into the underlying pathological changes in facial dyskinesias and palsy.

Patients with facial dyskinesias and palsy show distinct white matter geometric microstructural patterns. Meige's syndrome patients exhibit markedly altered white matter integrity and geometry, while facial palsy patients' white matter features correlate with clinical severity. Integrating traditional Diffusion Tensor Imaging measurements (fractional anisotropy and mean diffusivity) and Director Field Analysis‐based geometric metrics improves discrimination between facial dyskinesias and palsy.