Severe paraspinal muscle involvement in facioscapulohumeral muscular dystrophy

Objective: In this study, involvement of paraspinal muscles in 50 patients with facioscapulohumeral dystrophy (FSHD) was evaluated using MRI. Methods: The Dixon MRI technique was used in this observational study to quantify muscle fat content of paraspinal and leg muscles. Muscle strength in the neck, back, and legs was assessed with a handheld dynamometer. All subjects completed the Low Back Pain Rating Scale questionnaire. MRI findings were compared with 31 age-matched controls and correlated to muscle strength, back pain, and MRI findings in lower extremities. Results: The fat fraction in muscles was significantly higher in patients with FSHD than in controls: paraspinal fat fraction was 38% in patients vs 20% in controls, thigh fat fraction was 36% vs 11%, and calf fat fraction was 37% vs 11%. Increased paraspinal fat fraction correlated with D4Z4 repeat size, FSHD severity score, fat fraction of the thigh, and muscle strength in the back. The prevalence of back pain was 3 times higher in patients with FSHD vs controls, but back pain did not correlate with the paraspinal fat fraction. Conclusions: This study shows a prominent involvement of paraspinal muscles in patients with FSHD, which should be considered in the management of this condition.