Trunk Muscle Impairment and Pain in Myotonic Dystrophy type 1: Association to CTG size and Function

Myotonic Dystrophy 1 (DM1) is a progressive, hereditary neuromuscular disorder with multi-organ involvement. The genetic cause is an unstable CTG trinucleotide expansion in the DMPK gene at chromosome 19. Muscle involvement is expected to be distal in the extremities, the face and neck. Pain has not been described as part of the symptom complex. We investigated trunk muscle impairments, myopathy and pain in adult forms of DM1, and explored associations to function, CTG size and disease duration. In a cross-sectional design, 50 subjects with DM1 and 20 healthy age and gender-matched controls were included. Motor and psychological function, muscles and peripheral nerves were investigated. Clinical testing documented early and severe impairment in trunk muscles. An MRI study confirmed high degree of muscle fat infiltration and atrophy of trunk muscles. The clinical and radiological findings were significantly correlated to CTG size, disease duration, mobility, balance and respiration. We found high frequency of chronic pain (84%), most frequent locations were the lower back, neck and palmar side of the hands. Significant higher pain intensity and more pain locations was documented in women compared to men. In a sub study neuropathic pain was the probable mechanism in 15 %. Overall, pain was related to CTG size, quality of life, fatigue and respiration. In adult subjects with DM1, clinical impairment of trunk muscle function and objective findings of myopathy were clearly documented in our studies. These findings were related to motor function and CTG size. Pain was frequently reported, and gender differences significant. These findings suggest that follow up programs should include regularly assessment of trunk muscle function and pain in DM1. Whether trunk muscle impairment can be prevented or limited by exercise could be an important topic for a clinical intervention study. Pain studies accounting for gender differences should be conducted