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It is now generally accepted that the cause of megacolon is imbalance of the autonomic nerve stimuli to the colon. There are two neurogenic hypotheses. One is that excess of sympathetic activity by inhibiting colonic contraction and by contracting the sphincters produces constipation; the other that a diminished tonus of the parasympathetic innervation leads to poor peristaltic contraction and inefficient relaxation of the internal sphincter which disturbs the normal physiologic equilibrium.
Overactivity of the sympathetics is difficult to demonstrate clinically. Spinal anesthesia may be used as a test to block out the sympathetics and to see whether the bowels will move. This test, however, may block the parasympathetics as well and therefore the interpretation is equivocal. Consequently in the treatment of megacolon sympathectomy is usually done solely on an empirical basis.
In the last twelve years interruption of the sympathetic nerve to the colon has proved successful in relieving constipation
LAW JL. THE TREATMENT OF MEGACOLON WITH PARASYMPATHETIC DRUGS. JAMA. 1940;114(26):2537-2540. doi:10.1001/jama.1940.02810260023005