Neurogenic Bowel

Mr. RB was admitted from acute care to the spinal cord injury rehabilitation unit with significant constipation. He required a course of oral laxatives, enemas, and disimpaction to empty his bowels requiring several days.

Michelle R is the nurse responsible for Mr. RB as well as several other patients with acute traumatic spinal cord injuries at various levels. She is new to the unit, and interested in discussing with you bowel dysfunction in both the upper motor neuron bowel syndrome and the lower motor neuron bowel syndrome.

Q7. Describe how different SCI levels influence bowel function following SCI.
Depending on the level of injury, there are two distinct patterns in the clinical presentation of bowel dysfunction:

1. Injury above the conus medullaris results in upper motor neuron (UMN) bowel syndrome. The UMN bowel syndrome is typically associated with constipation and fecal retention.
2. Injury at the level of the conus medullaris and cauda equina results in lower motor neuron (LMN) bowel syndrome. LMN bowel syndrome is commonly associated with constipation, dry, hard stool and a significant risk of incontinence (due to incomplete anal sphincter control).

UMN bowel syndrome, or hyperreflexic bowel, is characterized by increased colonic wall and anal tone.Voluntary (cortical) control of the external anal sphincter is disrupted and the sphincter remains tight, thereby promoting retention of stool. However, the nerve connections between the spinal cord below the level of the lesion and the colon remain intact; therefore, there is preserved reflex coordination and stool propulsion.

LMN bowel syndrome, or areflexic bowel, is characterized by the loss of centrally-mediated (spinal cord) peristalsis and slow stool propulsion. A segmental colonic peristalsis occurs only due to the activity of the intrinsic myenteric plexus, resulting in the production of drier and round- shaped stool

Completeness of Injury also has a significant impact on bowel function in individuals with SCI. Those with an incomplete injury may retain the sensation of rectal fullness and ability to evacuate bowels so that no specific bowel program may be required.


Figure 4.Causes and symptoms of bowel dysfunction; physical character of stool is the pivotal variable that can shift the balance in either direction. Small, hard stool shifts the fulcrum to the left and more pressure is required to evacuate. Soft, bulky stool causes the fulcrum to shift the opposite way.

Figure 5. Balance of forces favoring continence or bowel evacuation. Physical character of stool is the pivotal variable that can shift the balance in either direction.