British Society for Clinical Neurophysiology

...to promote and encourage for the public benefit the science and practice of clinical neurophysiology and related sciences

Abstract Details

Electromyography in Collagen VI myopathy

Mutations in collagen VI (COLVI) cause a variety of muscular dystrophies of varying severity which include Bethlem myopathy on the milder end of the spectrum, Ullrich myopathy at the severe end and with a group of intermediate phenotypes in between. The clinical features include progressive muscle weakness, joint contractures and skin manifestations1. Histological changes on muscle biopsy are variable but may include fibre size variation with prominent muscle fibre hypertrophy. We hypothesised that muscle fibre hypertrophy results in a characteristic pattern on needle electromyography with high amplitude motor units of short or normal duration. Twelve patients with COLVI myopathy who had EMG as part of their diagnostic workup were identified, eleven of which had confirmed genetic mutations. Quantitative analysis of motor unit potentials was performed on at least 20 potentials and the average compared to published reference data2. A value was considered abnormal if it fell outside of two standard deviations for age. Automated turns amplitude analysis was also performed. No patients with short duration, low amplitude motor units characteristic of myopathy were identified. Six patients (50%) had high amplitude motor unit potentials of normal or short duration. Three patients had a neurogenic EMG pattern with high amplitude, long duration motor units. In the ten patients who had a muscle biopsy performed, fibre hypertrophy was noted to occur in varying degrees in eight patients. In the two patients without fibre hypertrophy the EMG was either reported as normal or showed only mild abnormalities. This study demonstrates that the EMG findings in COLVI myopathy are heterogeneous and challenging to interpret. Without performing quantitative motor unit potential analysis it would be possible to incorrectly characterise a significant proportion of these patients as having neurogenic conditions. High amplitude short or normal duration motor units may be the correlate of muscle fibre hypertrophy

TitleForenamesSurnameInstitutionLead AuthorPresenter
Dr DanielRuddRoyal London Hospital
Dr RocioCortesRoberto del Rio Hospital, Clinica Las Condes, Santiago, Chile.
Dr MatthewPittGreat Ormond Street Hospital
Reference
1. Bonnemann, G.G. 2011. The collagen VI-related myopathies: muscle meets its matrix. Nature Reviews Neurology. 7, 379-390
2. Jabre, J.F., Pitt, M.C., Deeb, J., & Chui K.K. 2015. E-norms: a method to extrapolate reference values from a laboratory population. J. Clin. Neurophysiology., 32, 265-70