Neurogenic bowel dysfunction (NBD) is reduced ability or inability to control defecation due to deterioration of or injury to the nervous system, resulting in fecal incontinence or constipation.

At a suitable time the brain can send signals causing the external anal sphincter and puborectalis muscle to relax as these are under voluntary control and this allows defecation to take place.

[4][5] Spinal cord injury and other neurological problems mostly affect the lower GI tract (i.e., jejunum, ileum, and colon) leading to symptoms of incontinence or constipation.

However, the upper GI tract (i.e., esophagus, stomach, and duodenum) may also be affected and patients with NBD often present with multiple symptoms.

[13] On the other hand, a lower motor neuron lesion can cause areflexia and a flaccid external anal sphincter so most commonly leading to incontinence.

Therefore, spina bifida affects the bowel similarly to a lower motor neuron spinal cord injury, resulting in a flaccid, unreactive rectal wall.

[5] There are a variety of symptoms associated with multiple sclerosis that are all caused by a loss of myelin, the insulating layer surrounding the neurons (nerve cells).

[12] In patients with multiple sclerosis, constipation and fecal incontinence often coexist, and they can be acute, chronic or intermittent due to the fluctuating pattern of MS.[5] Damage to the defecation centre within the medulla oblongata of the brain can lead to bowel dysfunction.

[12] The reduced dopamine levels also causes dystonia of the striated muscles of the pelvic floor and external anal sphincter.

[14][non-primary source needed] Twenty percent of people with diabetes mellitus experience fecal incontinence due to irreversible autonomic neuropathy.

This is due to the high blood glucose levels over time damaging the nerves, which can lead to impaired rectal sensation.

[15][16] Subconscious processes are controlled by the autonomic nervous system; these are involuntary movements such as contraction of the smooth muscle of the internal anal sphincter or the colon.

[14][non-primary source needed] Management and treatment for neurogenic bowel dysfunction depends on symptoms and biomedical diagnosis for cause of the condition.

[20] In the most severe of cases of neurogenic bowel dysfunction induced fecal impaction, surgical interventions like colostomy are used to disrupt the dense mass of stool.