Gastroduodenal motility in a case of dystrophia myotonica

A 53-year-old man with dystrophia myotonica developed symptoms of a chronic intestinal motility disorder. Incoordinate small bowel contractions as well as dilated segments were observed on x-ray examination. Gastroduodenal manometry in the fasted state showed contractions of reduced amplitude. A migrating motor complex occurred in the basal state. Pentagastrin and edrophonium injections increased motility; a liquid meal was followed by a normal motor response. The maximum gastric contraction rate (after pentagastrin injection) was 3.8/min. The maximum duodenal contraction rate observed at each duodenal recording site varied between 11.0 and 18.5/min. The lowest rate at each recording site was 11.1, 11.5, 11.0, and 11.2/min, while the fastest rate was 17.6, 16.6, 18.5, and 17.6/min. These maximum rates occurred independently of the rates at adjacent sites and of the drug infusions. The gastroduodenal motor abnormality in this patient thus predominantly affects smooth muscle, with the intrinsic neurons able to release acetylcholine and the muscle capable of responding to it. The results may indicate that electrical control activity in the duodenum intermittently oscillates more rapidly than normal, and when this occurs, phase-locking is absent. We conclude that in dystrophia myotonica there may be a defect in the cell membrane, which can cause more frequent electrical oscillations of the cell; alternatively, there may be a defect in cell-to-cell coupling.