Spin-lock magnetic resonance imaging of muscle in patients with autosomal recessive limb girdle muscular dystrophy.

Spin-lock imaging is a new magnetic resonance imaging (MRI) technique used to reflect the microstructural integrity of muscle. The purpose of this study was to characterize spin-lock contrast (SLC) of calf muscles in limb girdle muscular dystrophy (LGMD). The calf muscles of 5 patients with LGMD and 10 healthy volunteers were imaged with an off-resonance magnetic resonance (MR) spin-lock suppression pulse. Spin-lock suppression ratios were calculated for anterior tibialis, posterior tibialis, soleus, and gastrocnemius muscles. Clinical assessments of muscle strength were compared to the spin-lock suppression ratios in the LGMD group. Strong SLC was observed in healthy muscles, with mean (+/- SD) suppression ratios ranging from 51.2% (+/- 3.6%) to 56.3% (+/- 1.3%). In diseased muscle, spin-lock signal suppression was reduced by 8%-70%, demonstrating an inverse correlation between symptom duration and suppression ratios. Spin-lock contrast in the patients with LGMD, as a reflection of tissue integrity, was best preserved in posterior tibialis, anterior tibialis, soleus, and gastrocnemius muscles in descending order. Clinical assessments did a poorer job of differentiating than SLC did and were in poor agreement with spin-lock suppression ratios. Spin-lock MRI can quantify microstructural changes in LGMD and appears to provide information not obtainable from clinical evaluations. This suggests that this noninvasive technique may be useful in evaluating the extent, progression, and response to therapy of LGMD.

Magnetization transfer imaging of skeletal muscle in autosomal recessive limb girdle muscular dystrophy.

PURPOSE: The purpose of this work was to characterize magnetization transfer (MT) contrast of skeletal muscles in limb girdle muscular dystrophy (LGMD). METHOD: The calf muscles of five LGMD patients and 10 normal volunteers were imaged with an off-resonance MT suppression pulse applied to T1-weighted images. MT suppression ratios were calculated for anterior tibialis, posterior tibialis, soleus, and gastrocnemius muscles in the LGMD and control groups. The relationship between MT of individual muscles and the duration of LGMD symptoms was determined. RESULTS: Strong MT contrast was observed in normal calf muscles, with mean (+/-SD) suppression ratios ranging from 37.9% (+/-3.0) to 41.1% (+/-2.1). In diseased muscle, MT signal suppression ranged from 11 to 38%, demonstrating an inverse relationship between symptom duration and suppression ratios. MT contrast in the LGMD patients, as a reflection of muscle tissue integrity, was preserved in posterior or anterior tibialis, soleus, and gastrocnemius muscles, respectively. Suppression ratios were dramatically reduced in muscles with gross fatty infiltration but also were reduced in muscle tissues without visual evidence of fatty infiltration. CONCLUSION: MT imaging provides a quantitative measure of pathologic changes occurring within the skeletal muscles of patients with LGMD relative to normal and may be useful in evaluating disease extent, progression, and response to new therapies as they become available.