Autonomic Dysreflexia - Causes

Causes

The most common causes of autonomic hyperreflexia seen in patients with spinal cord injury are loss of bowel and bladder function, resulting in impaction in the case of the bowels and distention in case of the bladder. These are generally found in patients with a spinal cord injury above the T6 (6th Thoracic Vertebral) level, but can occur in patients with a transection as low as T10 (10th Thoracic Vertebral) level.

Another causative factor may be an undetected urinary tract infection. The difficulty in assessing this may be complicated with the usage of indwelling or suprapubic catheters. When a painful stimulus occurs, as when voiding is interrupted or a bowel obstruction occurs, nerve impulses are sent to the brain via the spinal cord. However, in spinal cord transection, these impulses are unable to travel past the injury. This results in a spinal cord reflex to the autonomic nervous system in response to pain. In patients with spinal cord transection, types of stimulation that are tolerated by healthy people create an excessive response from the person's nervous system.

Other causes include medication side effects and various disease processes. The use of stimulants such as cocaine and amphetamines which can result in urinary retention, and the use of CNS depressants and other and psychoactive drugs can also lead to urinary retention and constipation thus leading to autonomic dysreflexia when in use over an extended period of time. Guillain-Barre syndrome a demyelinating disease that can result in peripheral paralysis can progress to encompass autonomic functions leading to a loss of normal respiratory, bladder and bowel function, thus resulting in autonomic dysreflexia. Severe head trauma, and other brain injuries can instigate autonomic dysreflexia at the Central Nervous System by interfering with the reception of the signal that brings the urge to void the bladder and bowels and with the volutary abiliity to micturate and defecate. Other causal theories for Autonomic Dysreflexia include Noxious Stimuli or painful stimuli arising from the peripheral sensory neurons. These stimuli are interrupted in their journey to the brain due to a transection of the spine result in a paradoxical stimulation of autonomic pathways of the Autonomic Nervous System.

Controversy Over Peripherally Noxious Causes of Autonomic Dysreflexia

Current scientific literature suggests that noxious (painful) stimuli are the primary initiators of AD. However, different studies have found that activation of pain receptors in muscle and skin below the lesion in spinal cord injured individuals did not trigger AD. These studies suggests that not all noxious stimuli are reliable triggers of AD, and because non-noxious stimuli can also trigger AD, attribution of an episode of AD to noxious stimuli may cause clinicians to overlook underlying non-noxious triggers. As a result, non-noxious trigger factors remain undetected, prolonging an episode of AD. They concluded that when deducing the potential causes of AD it is important to consider non-noxious sources of stimulation in addition to noxious triggers. Current Assessment of Autonomic Dysreflexia in patients with known causitive factors include palpation of the bladder and bowel and can also include bladder scan.