Radiological correlates of vocal fold bowing as markers of Parkinson’s disease progression: A cross-sectional study utilizing dynamic laryngeal CT

Abstract

Objective To determine whether arytenoid cartilage position and dynamics change with advancing duration and severity (as graded by MDS-UPDRS part III scores) in Parkinson’s disease, in a cross-sectional study design, we performed laryngeal four-dimensional computed tomography (4D-CT) in people with Parkinson’s disease and controls. Methods 31 people with Parkinson’s disease covering a range of disease duration and severity and 19 controls underwent laryngeal 4D-CT whilst repeatedly vocalizing. We measured on each CT volume the glottic area (GA), inter-arytenoid distance (IAD), IAD-Area index (IAI) and arytenoid cartilage velocity (av→). Results People with Parkinson’s disease had reductions in the mean/effective minimum IAD when compared to controls, while mean/effective minimum GA and mean/effective maximum IAI were increased. Arytenoid cartilage velocities showed no difference. On Spearman correlation analyses, advancing disease duration and severity of PD showed moderately strong and significant correlations with increasing mean/effective minimum GA, increasing mean/effective maximum IAI and decreasing effective minimum IAD. Linear mixed models which considered the effects of intra and inter-individual variation showed that both disease duration (b = -0.011, SEb = 0.053, 95% CI [-0.022, 0], t(27) = -2.10, p = 0.045) and severity (b = -0.069, SEb = 0.032, 95% CI [-0.14,-0.0039], t(27) = -2.17, p = 0.039) were significant predictors for IAD, and also for transformed values of the GA and IAI. Conclusions There are progressive alterations in phonatory posturing as Parkinson’s disease advances. The increases in GA despite reductions in IAD are concordant with prior observations of vocal fold bowing. Our study provides a basis for using laryngeal 4D-CT to assess disease progression in Parkinson’s disease.

Automated measurement of inter-arytenoid distance on 4D laryngeal CT: A validation study

“…We hypothesized that a repetitive vocalization task with laryngeal 4D-CT could reveal differences in arytenoid cartilage movements between pwPD and healthy control participants. In our prior work [ 11 , 12 ], two key measurements were taken which were 1) the minimum distance between the arytenoid cartilages (denoted the inter-arytenoid distance or IAD), and 2) the glottic area. We previously demonstrated that changes to arytenoid cartilage posturing distinguish pwPD from healthy controls.…”

“…We previously demonstrated that changes to arytenoid cartilage posturing distinguish pwPD from healthy controls. pwPD have a reduction in the IAD and an increase in the glottic area during vocalization [ 11 , 12 ]. We also found that as the condition advances over both time and clinical severity, the IAD progressively decreases while the glottic area increases [ 12 ].…”

“…Measurement of the rotational movements would require landmarks such as the vocal and muscular processes to be marked, but these are not always reliably identified on CT. In our study, we were only able to reliably mark the base of the vocal processes [ 12 ]. As the vocal folds attach to the tip of the vocal processes, IAD as we measure it does not exactly correspond to vocal fold adduction.…”

“…Understanding the hypokinetic hypophonic dysarthria of PD is complicated by the laryngoscopic finding of glottic incompetence due to bowing of the vocal folds [ 13 , 14 , 18 ]. The increase in glottic area in pwPD despite a reduced IAD is a surrogate marker for vocal fold bowing [ 12 ] and this may explain the breathiness of the voice that can be appreciated in pwPD [ 19 , 20 ].…”

“…This represents the error in the placement of the individual fiducial markers; the IAD between the fiducial markers was not calculated in this study. The mean IAD during a vocalization task in our cohort of pwPD of varying duration and severities was 4.24 mm, while it was 5.21 mm in control participants (comparing the unadjusted median)–a difference of only 0.97 mm [ 12 ]. In our study comparing pwPD with relatively early-stage disease against controls, adjusted for sex, the mean difference was 0.87 mm [ 11 ].…”