Association between the Phase Angle and the Severity of Horizontal Gaze Disorder in Patients with Idiopathic Dropped Head Syndrome: A Cross-Sectional Study.

Background and Objectives: The phase angle, calculated by bioelectrical impedance analysis, can help elucidate the pathology of patients with idiopathic dropped head syndrome (IDHS) and explain the motor dysfunction associated with the horizontal gaze disorder. The aim of this study was to clarify the characteristics of phase angle in IDHS patients and the relationship between the phase angle and the severity of horizontal gaze disorder. Materials and Methods: This cross-sectional study included 43 female patients with IDHS and 69 healthy female volunteers. A multi-frequency segmental body composition analyzer was used to calculate body composition parameters, including whole-body and lower extremity phase angles. Propensity score (PS) matching analysis was performed to compare the body composition parameters between the IDHS and healthy groups. Variables that determine the PS were identified by correlation analysis, using the whole-body phase angle as the dependent variable. In addition, correlation analysis was performed between the severity of horizontal gaze disorder as assessed by McGregor's slope (McGS), phase angle, and other body composition parameters. Results: Unadjusted group comparisons showed no significant difference in whole-body and lower extremity phase angles between the IDHS and healthy groups. PS matching created a total of 38 matched pairs for age, height, and fat-free mass index. Although the comparison between groups of matched samples showed no significant difference in the whole-body phase angle, the lower extremity phase angle in the IDHS group was significantly lower than that in the healthy group (p = 0.033). Correlation analysis showed significant negative correlations only between McGS and whole-body (r = -0.31, p = 0.043) and lower extremity phase angle (r = -0.39, p = 0.009) in the IDHS group. Conclusions: Abnormal body composition of the lower extremities were observed in IDHS patients. Furthermore, it was suggested that horizontal gaze disorder in IDHS patients is associated with whole-body and lower extremity phase angles.