Abstract
Practice of sports during childhood or adolescence correlates with an earlier onset and more rapidly progressing phenotype in dysferlinopathies. To determine if this correlation relates to greater muscle pathology that persists into adulthood, we investigated the effect of exercise on the degree of muscle fatty replacement measured using muscle MRI. We reviewed pelvic, thigh and leg T1W MRI scans from 160 patients with genetically confirmed dysferlinopathy from the Jain Foundation International clinical outcomes study in dysferlinopathy. Two independent assessors used the Lamminen-Mercuri visual scale to score degree of fat replacement in each muscle. Exercise intensity for each individual was defined as no activity, minimal, moderate, or intensive activity by using metabolic equivalents and patient reported frequency of sports undertaken between the ages of 10 and 18. We used ANCOVA and linear modeling to compare the mean Lamminen-Mercuri score for the pelvis, thigh, and leg between exercise groups, controlling for age at assessment and symptom duration. Intensive exercisers showed greater fatty replacement in the muscles of the pelvis than moderate exercisers, but no significant differences of the thigh or leg. Within the pelvis, Psoas was the muscle most strongly associated with this exercise effect. In patients with a short symptom duration of <15 years there was a trend toward greater fatty replacement in the muscles of the thigh. These findings define key muscles involved in the exercise-phenotype effect that has previously been observed only clinically in dysferlinopathy and support recommendations that pre-symptomatic patients should avoid very intensive exercise.
Highlights
Dysferlinopathy is an autosomal recessively inherited form of muscular dystrophy caused by mutations in the DYSF gene
In this study we use T1W images from this previously described cohort, in combination with questionnaire derived information about pre-symptomatic activity levels to objectively assess the impact of teenage exercise on muscle fat replacement. We review if this supports the patient reported earlier onset and more rapid loss of ambulation in intensive exercisers, if exercise has differential effects in muscle, such that some muscles are more impacted than others and if conclusions can be reached about the types of exercise that may be detrimental in dysferlinopathy
Patient reported age of symptom onset was later in the inactive group 0 than in all of the other exercise groups (Table 1)
Summary
Dysferlinopathy is an autosomal recessively inherited form of muscular dystrophy caused by mutations in the DYSF gene. Eccentric muscle contractions (such as running) cause more rapid progression of muscular dystrophy pathology and greater functional weakness, while concentric muscle contraction (such as swimming) appeared to be protective against both general disease progression and in mitigating the myofiber damage caused by subsequent eccentric muscle contraction [5, 6]. This finding clearly has implications for patients in terms of the type or intensity of exercise that should be recommended. Pathological differences depending on exercise type or intensity have not been assessed and it is not clear if early influences of exercise would remain detectable after many years of symptomatic disease
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