Affection of the Gastrointestinal Smooth Muscles in Myotonic Dystrophy Is Not Unusual.

To the Editor We read with interest the article by Sato et al. concerning a 54-year-old woman with myotonic dystrophy who developed achalasia that was initially attributed to myotonia and later to weakness of smooth muscle cells (1). We have several comments and concerns about this article.

Myotonic dystrophy refers not only to myotonic dystrophy-1 (MD1) but also myotonic dystrophy-2 (MD2), which has a similar phenotype. Since the authors did not specify the type of myotonic dystrophy, they should clarify whether the patient had MD1 or MD2. We also should be informed about the number of CTG-repeats in dystrophia myotonica protein kinase (DMPK), respectively CCTG-repeats in ZNF9. This is of relevance, as the phenotype is related to the repeat length in DMPK respectively ZNF9 (2).

A further shortcoming of the report is that it was not mentioned which clinical manifestations occurred at the onset and led to the suspicion of MD1/MD2. Digestive problems have been previously reported to precede other clinical manifestations of MD1 (3). Was achalasia truly the initial manifestation of the disease?

Affection of the smooth muscle cells in MD1/MD2 may lead to gastroparesis, delayed gastric emptying, and dyspepsia (4). The authors should clarify if the index patient complained about symptoms indicative of delayed gastric emptying or gastroparesis. Other gastrointestinal manifestations of MD1/MD1 include megacolon, chronic constipation, bloating, heartburn, and regurgitation (4).

Achalasia is frequently associated with reflux disease/esophagitis. The authors should clarify if esophagitis was present in the index patient and if it improved upon symptomatic treatment. Fundoplication can be performed for invasive treatment of achalasia; it has been previously reported as a therapeutic option for achalasia in MD (5). Did the authors consider surgery to alleviate achalasia?

Achalasia was initially attributed to myotonia of the lower esophagial sphincter (LES) (1). The authors should clarify if the patient also had myotonia of the skeletal muscles when achalasia was first diagnosed. The authors should clarify if the patient was treated with mexiletine for myotonia of the LES, which has an anti-myotonic effect, and if mexiletine was beneficial for myotonic achalasia.

Since the outcome of MD1/MD2 strongly depends on the degree of cardiac involvement, The authors should clarify if the index patient had AV-blocks, ventricular arrhythmias, hypertrophic cardiomyopathy, dilated cardiomyopathy, or non-compaction. It should be mentioned if achalasia affected the vagal nerve and consequently the heart rhythm and propensity for developing arrhythmias.

Overall, this interesting article could be more meaningful if the points outlined above were addressed. We require detailed descriptions of exceptional cases of myotonic dystrophy.

The authors state that they have no Conflict of Interest (COI).