Sir.—I read with great interest the article entitled "Neonatal Dystrophia Myotonica: Electrophysiologic Studies" by Swift et al in the June 1975 issue of the Journal (129:734-737, 1975). The point they make about the possibility of confirming a diagnosis of dystrophia myotonica in the newborn period with electromyography is very important, not only to help identify this disorder or others in which myotonia is a feature, but to differentiate this disorder from others appearing in the newborn period with hypotonia, as the authors state.
The patient with neonatal dystrophia myotonica presented by the authors had an abnormal electromyogram (EMG) on the fifth day of life. They also list three other reported cases of neonatal dystrophia myotonica, in which the EMGs were abnormal at an early age (6 weeks, 3 months, and 9 months, respectively). To underline the potential usefulness of an EMG in the very young infant suspected of having