Is the digestive system affected in ALS?

ALS affects voluntary motor function and spares all muscles that are not under voluntary control. As a result, the muscles of the gastrointestinal tract are not directly affected.

Nevertheless, digestion may be indirectly impaired. For example, a swallowing disorder may require adjustments to the diet. This includes changes in eating habits and food composition, and may even extend to the use of liquid nutrition or tube feeding via a PEG. Changes in dietary composition—particularly in the proportion of dietary fiber—can be associated with diarrhea or constipation. In most cases, these undesirable effects of the dietary changes can be alleviated by further adjusting the diet. This is where dietitians provide crucial support, as they possess the necessary expertise to adapt meals—and, if necessary, specialized nutritional products—to the new situation.

Limited mobility is another factor that affects digestion. A decrease in physical activity—particularly walking upright—and an increase in time spent sitting or lying down have an adverse effect on digestive function. Regular physical therapy, the use of therapeutic exercise equipment, therapy tables, and standing wheelchairs—depending on the situation and the course of the disease—help improve digestion and prevent constipation.

Unlike the intestinal muscles, the muscles of the abdominal wall are affected in ALS (they can be voluntarily contracted and are controlled by motor neurons). The muscle tone of the abdominal wall provides a baseline tension within the abdominal cavity, which is also important for bowel movement. Motor weakness of the abdominal wall is thus one of several factors that contribute to constipation. This is where a specialized form of physical therapy known as colon massage comes into play. This refers to external massage of the abdominal wall, which is intended to support the weakened motor function of the abdominal wall and stimulate bowel movements. Overall, constipation is the most common indirect symptom affecting the digestive system in ALS and requires the identification, consideration, and treatment of the various underlying factors.