G.P.83 Temporal muscle hypertrophy and skull morphology in DMD patients

Abstract

Hypertrophy is an adaptive response of muscle. This is a well-known phenomenon of the calve muscles in Duchenne muscular dystrophy (DMD), but less well studied in other dystrophic muscles. In DMD chewing and biting are important motor skills that can be affected by the disease. Decreased bite force can be observed in patients from the age of eight years on. Imbalance of muscle strength influences growth and development in the orofacial region and resulting in anatomical variations, like dental malocclusion. In an ongoing MRI study on brain morphology in boys with DMD we observed marked hypertrophy of the temporal muscles. This prompted us to study these muscles in more detail and to investigate the consequences for skull morphology. MR images of 15 boys with DMD (age 12.4±2.7y) and 15 healthy age-matched boys (age 12.4±1.7y) were compared. Regions of interest of the head, skull and temporal muscles were manually drawn on transversal T1w images and averaged for 10 slices. Analysis on temporal muscle size, head size and eccentricity (roundness) of the skull was performed. All DMD boys had temporal muscle hypertrophy. The cross-sectional size of the temporal muscles was significantly larger in DMD (p<0.0001) compared with controls, with on averaging doubling in size. The head circumference was not different between the two groups. There was a significantly different eccentricity of the skull between DMD and healthy boys (p=0.03). The differences in skull morphology in DMD appeared to be more prominent in older boys. Muscle hypertrophy in DMD is not restricted to larger skeletal muscles. Hypertrophy of the temporal muscles and possibly of other orofacial muscles indicates early involvement of these muscles in DMD and probably contributes to the changes in skull morphology.