Myotonia is a phenomenon characterized by a tonic preservation of muscular contraction.1 It is elicited by a voluntary forceful contraction or by mechanical percussion of the muscle. In Thomsen's disease (myotonia congenita) the myotonia may be evoked in any skeletal muscle group and may be quite prominent in the orbicularis oculi.2 Repetition of movement usually results in a disappearance of myotonia, while cold and fatigue commonly are aggravating factors. The electromyogram (EMG) in Thomsen's disease shows increased electrical activity with muscular movement and, most characteristically, a prolonged train of regular and synchronous potentials after muscular contraction or stimulation.
Hoffmann3 in 1896 described a young man with myotonia occurring simultaneously with hypothyroidism. Associated were prominent strongly developed muscles and percussion myotonia. The electrical stimulation of the affected muscles differed from that seen in Thomsen's disease. The patient was improved with thyroid hormone therapy, and the myotonia apparently disappeared.