The needle EMG findings in myotonia congenita

Introduction Myotonia congenita (MC) is caused by pathogenic variants in the CLCN1 gene coding the chloride channel protein. Methods To test the hypothesis that needle EMG could be helpful in distinguishing between the recessive and dominant MC, we performed EMG examination in 36 patients (23 men) aged 4–61 years with genetically proven MC: in 30 patients with autosomal recessive MC (Becker MC) and in 6 with autosomal dominant MC (Thomsen MC). Results Myotonic discharges were recorded in 95.8% of examined muscles. For the whole MC group we observed a significant positive correlation between parameters of motor unit activity potentials (MUAPs) in vastus lateralis and tibialis anterior muscles and the duration of the disease. Similar correlation for biceps brachii also was found in Becker MC subgroup only. Discussion EMG could still be helpful in diagnosis of MC and together with provocative tests might be useful in differentiation between recessive and autosomal MC.