Quantifying muscle glycosaminoglycan levels in patients with post-stroke muscle stiffness using T1ρ MRI

Abstract

The purpose of this study was to provide imaging evidence of increased glycosaminoglycan (GAG) content in patients with post-stroke muscle stiffness; and to determine the effect of hyaluronidase treatment on intramuscular GAG content. In this prospective study, we used 3D-T1ρ (T1rho) magnetic resonance (MR) mapping of the upper arm muscles to quantify GAG content in patients with post-stroke muscle stiffness before and after hyaluronidase injection treatment. For this study, healthy controls (n = 5), and patients with post-stroke muscle stiffness (n = 5) were recruited (March 2017-April 2018). T1ρ MR imaging and Dixon water-fat MR imaging of the affected upper arms were performed before and after off-label treatment with hyaluronidase injections. T1ρ mapping was done using a three-parameter non-linear mono-exponential fit. Wilcoxon Mann-Whitney test was used to compare patients' vs controls and pre- vs post-treatment conditions. The T1ρ values in the biceps were significantly higher in patients before treatment (34.04 ± 4.39 ms) compared with controls (26.70 ± 0.54 ms; P = 0.006). Significant improvement was seen in the biceps of patients before (35.48 ± 3.38 ms) and after treatment (29.45 ± 1.23 ms; P = 0.077). Dixon water-fat distribution was not significantly different in the patients compared to the controls (biceps P = 0.063; triceps P = 0.190). These results suggest that T1ρ mapping can be used to quantify GAG content in the muscles of patients with post-stroke muscle stiffness, and that muscle hyaluronan content is increased in stiff muscles compared with controls, providing imaging corroboration for the hyaluronan hypothesis of muscle stiffness.

Conflict of interest statement

New York University has filed a patent on hyaluronidase for muscle stiffness. This study employs an off-label use of an FDA approved enzyme, hyaluronidase. PR is co-founder of Movease, Inc.

Figures

Figure 1

Schematic representation describing the T1ρ mapping process. (A) The T1ρ weighted images from all TSL durations are fit on a pixel by pixel basis using a 3 parameter fit mono-exponential model to fit the data in each voxel to produce a T1ρ map. (B) Shows typical manually drawn ROIs for biceps and triceps muscles.

Figure 2

T1ρ maps for a representative control subject and patient (pre-treatment). (A) Shows T1ρ maps of 3 representative slices overlaid over anatomy in a control subject. (B) Shows T1ρ maps of three representative slices overlaid over anatomy in a patient with post-stroke muscle stiffness prior to hyaluronidase injection treatment.

Figure 3

Representative T1ρ maps before and after hyaluronidase injection treatment. (A) Show T1ρ maps of representative slices overlaid over anatomy from 3 patients with post-stroke muscle stiffness before injections were administered (B) Shows T1ρ maps of the same patients in (A) at approximately similar slice locations following hyaluronidase injection treatment. Note the difference in shape of the muscle before and after the injections.

Figure 4

Comparison of mean T1ρ values between groups. (A) Shows the comparison of mean T1ρ values in the biceps and triceps ROIs between controls and pre-injection patients (N = 5). The T1ρ values expressed as mean ± SD are shown. In the biceps ROI, there is a significant different in the mean T1ρ value (P = 0.005), while a significant difference in the triceps ROI is not observed (P = 0.14) (B) Shows the comparison of mean T1ρ values in the biceps and triceps ROIs between pre- vs post-injection patients expressed as mean ± SD values. For the biceps ROI, a significant difference was observed between pre- and post-injection patients (P = 0.077), but a significant difference was not observed for the triceps ROI between pre- and post-injection (P = 0.65). Significance level set to 0.1, owing to the lower sample size (N = 3).

Figure 5

Assessment of fatty infiltration in upper arm muscles using Dixon water-fat imaging. (A) Shows the T1ρ map of a healthy control subject, (B) shows the T1ρ map of patient before treatment (C) shows the calculated results from the Dixon water-fat imaging showing the water image, fat image, water fraction and fat fraction in the control subject in A and in the patient in B before treatment (D). Although the triceps and biceps ROIs showed increases in fat fraction in the skeletal muscle of patients, the differences were not significant compared to controls (P = 0.063 for biceps, P = 0.19 for triceps) suggesting that fatty infiltration did not play a big role in the elevation of T1ρ values.

Figure 6

Model of the evolution of muscle biochemical/structural changes post stroke. (A) Shows a cross-section of a normal skeletal muscle, (B) shows the evolution of muscle stiffness following post-stroke paralysis and immobility that results in accumulation of hyaluronan in the extracellular space, increasing the viscosity of the ECM, and causing the muscle fibers to stick together (C) shows that continued inflammation, immobility and muscle stiffness initiates fibrosis leading to the replacement of hyaluronan by collagen, thickened endomysium and perimysium, and muscle fiber atrophy. Note that while (C) depicting fibrosis is an irreversible stage, data from literature suggests that the processes between stages depicted in (A) and (B) are reversible and may represent a potential therapeutic target.