Myotonic dystrophy is a rare and slowly progressive neuromuscular disease caused by genetic defects. To date, two forms of myotonic dystrophy have been identified: myotonic dystrophy type 1 (DM1 or Steinert’s disease) and myotonic dystrophy type 2 (DM2 or PROMM). Myotonic dystrophy is characterized by progressive myopathy, muscle weakness, multiorgan failure involvement, and myotonia. Myotonia can be defined as excessive and prolonged muscle excitability and muscle contraction at rest, right after muscle percussion or at the end of the excitatory stimulus. It is possible to identify two forms of myotonia: clinical myotonia that consists in incomplete relaxation of muscle following either voluntary contraction or direct percussion, and electric myotonia that is an abnormal muscle fibre membrane electrical activity observed by needle EMG examination.