Myotonia is a symptom of muscle disease, the essence of which is an obstructed diastasis of the muscle and its stiffness. This symptom occurs in the course of various disease entities. Myotonic activity originates in the muscle cell and clinically manifests as active myotonia or percussive myotonia. Myotonic syndromes are divided into non-dystrophic myotonia and myotonic dystrophies. The diagnosis of myotonic syndromes is based on electromyographic (EMG) examination.