Guillain-Barré syndrome (see Chap. 43), pure pandysautonomia, and severe diabetic autonomic neuropathy discussed earlier. In a few cases of the latter, antibodies against the alpha subunit of the ganglionic acetylcholine receptor has been found by Vernino and colleagues. Systemic diseases may affect the colonic sphincters; examples are myotonic dystrophy and scleroderma, which may weaken the internal sphincter, and polymyositis and myasthenia gravis, which may impair the function of the external sphincter and allow bowel gas to escape (Schuster). The inability to control flatulence may be an early sign of skeletal muscle sphincteric weakness in myasthenia. Also, sphincteric damage may complicate hemorrhoidectomy.
In recent years there has been considerable interest in weakness of the muscles of the pelvic floor as a cause of double incontinence, especially in the female. Also, it has been suggested that paradoxical contraction of the puborectus and external anal sphincter may be a cause of severe constipation (anismus). Extreme degrees of descent of the pelvic floor are believed to injure the pudendal nerves, as reflected in prolonged terminal latencies in nerve conduction studies.
Many cases of ileus, even to the extent of megacolon, have a pharmacologic basis, being a result of the use of drugs that paralyze the parasympathetic system or narcotics that have a direct effect on the motility of gastrointestinal smooth muscle.
The serotonin receptor agonist cisapride had been used in partially restoring gastrointestinal motility in some cases of neurogenic ileus as, for example, the early stages of the Guillain-Barré syndrome and in pediatric bowel diseases. Because of ventricular arrhythmias and a few cases of sudden cardiac death, its administration is currently allowed only by experienced pediatric gastroenterologists.
This is a rare disease affecting mainly male infants and children. It is caused by a congenital absence of ganglion cells in the myenteric plexus. The internal anal sphincter and rectosigmoid are involved most often and are the parts affected in restricted forms of Hirschsprung disease (75 percent of cases), but the aganglionosis is sometimes more extensive. The aganglionic segment of the bowel is constricted and cannot relax, thus preventing propagation of peristaltic waves, which, in turn, produces retention of feces and massive distention of the colon above the aganglionic segment. Enterocolitis is the most serious complication and is associated with a high mortality. Some cases of megaloureter are attributed to a similar defect.
Hirschsprung disease in most cases has been traced to a mutation of the RET oncogene and perhaps to polymorphisms in other genes; the variability in clinical severity corresponds to polymorphisms in the responsible gene. Other genes, such as the one that codes for the endothelin receptor, are implicated in a small group with the disease. There are several other familial diseases that may manifest as an enteric neuropathy including an unusual mitochondrial disorder discussed in Chap. 36, Allgrove syndrome, and an entity termed familial visceral myopathy.
Disturbances of Sexual Function
Sexual function in the male, which is not infrequently affected in neurologic disease, may be divided into several parts: (1) sexual impulse, drive, or desire, referred to as libido, discussed in Chap. 24; (2) penile erection, enabling the act of sexual intercourse (potency); and (3) ejaculation of semen by the prostate through the urethra.