# Quantification of enlargement of the levator palpebrae superioris muscle in thyroid eye disease

## TL;DR

This study shows that the levator palpebrae superioris muscle is enlarged in nearly half of thyroid eye disease cases, using detailed MRI measurements.

## Contribution

This is the first study to individually segment and quantify the enlargement of the levator palpebrae superioris muscle in thyroid eye disease.

## Key findings

- LPS enlargement occurred in 48.7% of TED orbits.
- The LPS in TED had a mean thickness of 2.4 mm, significantly higher than the non-TED group.
- The LPS to SR size ratio was not significantly different between TED and non-TED groups.

## Abstract

Thyroid eye disease (TED) is an autoimmune-mediated inflammatory condition of the orbit leading to hypertrophy and inflammation of the orbital extra-ocular muscles (EOMs). Previous studies have sought to quantify this enlargement, but due to the anatomical proximity and limitations in imaging quality, have measured the superior rectus (SR) and Levator Palpebrae Superioris (LPS) complex together rather than measuring the individual muscles.

Retrospective manual measurements from high-field (3-Tesla) fat-suppressed contrast-enhanced T1-weighted magnetic resonance imaging (MRI) of the orbits were taken from patients diagnosed with TED. To produce a control group, orbital MRIs were measured from patients being investigated for other non-TED related orbital pathology.

47 patients were included with TED with 78 orbits measured (L: 42 R: 37). In the control group, 111 patients with 163 orbits measured were included. In the TED cohort the mean ratio of LPS to SR size was 1.04 (SD: 0.53) compared to 0.947 (SD 0.33) in the non-TED cohort with no statistically significant difference (p = 0.3381). The LPS in the TED cohort had a mean muscle thickness of 2.4 mm (SD 0.895), which was higher than the non-TED cohort (p < 0.01) which had a mean thickness of 1.56 mm (SD 0.36). This study found LPS enlargement occurred in 48.7% of TED orbits.

This study demonstrates that absolute LPS enlargement is a common finding in TED, occurring in nearly half of affected orbits. This is the first study to individually segment and quantify the extent of enlargement of the LPS relative to the SR using modern medical imaging.