All About Autonomic Dysreflexia (or Hyperreflexia)

Written by Christine Case-Lo | Published on August 16, 2012
Medically Reviewed by George Krucik, MD

What Is Autonomic Dysreflexia?

Autonomic dysreflexia (AD) is a condition where the involuntary nervous system overreacts to external or bodily stimuli. This reaction causes a dangerous spike in blood pressure, racing heart, constriction of peripheral blood vessels, and other changes in the body’s autonomic functions.

AD is also known as autonomic hyperreflexia.

The condition is most commonly seen in people with spinal cord injuries above the sixth thoracic vertebra (T6). It may also affect people with multiple sclerosis, Guillain-Barre syndrome, and some head or brain injuries. Sometimes the condition is a side effect of medication or illegal drugs such as cocaine and amphetamines.

AD is potentially life threatening and can result in stroke, retinal hemorrhage, cardiac arrest, and pulmonary edema if not addressed quickly. AD is a very serious condition and is considered to be a medical emergency.

What Causes Autonomic Dysreflexia?

To understand autonomic dysreflexia, it is helpful to know something about the autonomic nervous system (ANS).

The ANS is the part of the nervous system responsible for involuntary bodily functions such as:

  • blood pressure
  • heart and breathing rates
  • body temperature
  • digestion
  • metabolism
  • balance of water and electrolytes
  • production of body fluids
  • urination
  • defecation
  • sexual response

The ANS is divided into two branches:

  • the sympathetic autonomic nervous system (SANS)
  • the parasympathetic autonomic nervous system (PANS)

The SANS and PANS are like the yin and yang of your nervous system. They operate in parallel, but opposite, ways to maintain the balance of the involuntary functions in your body. In other words, if the SANS overreacts, the PANS is able to compensate for it.

Here’s an example. If you see a bear, your sympathetic nervous system might initiate a “fight or flight” reaction. This would cause your heart to beat faster, your blood pressure to rise, and your blood vessels to get ready to run. But what if you were mistaken and just thought you saw a bear? You wouldn’t need the stimulation of your SANS, so your parasympathetic nervous system would jump into action. Your PANS would bring your heartbeat and blood pressure back to normal.

In autonomic dysreflexia, both the sympathetic and the parasympathetic nervous systems are disrupted. As a result, not only can the body’s SANS overreact to stimuli such as a full bladder, but also the PANS can’t effectively stop that reaction and may actually make it worse.

What Triggers Autonomic Dysreflexia?

With spinal cord injuries, your lower body is still generating a lot of nerve signals communicating the status of your bladder, bowels, digestion, and other bodily functions. The signals cannot get past the spinal injury to your brain. However, they are still being transmitted to the sympathetic and parasympathetic autonomic nervous systems that operate below the spinal cord injury. This means that signals from your bodily functions can trigger the SANS and PANS, but the brain cannot appropriately respond to them. They can no longer work effectively as a team. The result is that the SANS and PANS can get out of control.

Triggers for autonomous dysreflexia in persons with spinal cord injuries can be anything that generates nerve signals to the SANS and PANS, including:

  • distended bladder
  • blocked catheter
  • urinary retention
  • urinary tract infection
  • bladder stones
  • constipation
  • bowel impaction
  • hemorrhoids
  • skin irritations
  • pressure sores
  • tight clothing

What Are the Symptoms of Autonomic Dysreflexia?

Symptoms of AD may include:

  • anxiety and apprehension
  • irregular or racing heartbeat
  • nasal congestion
  • high blood pressure, with systolic readings often over 200mm Hg
  • pounding headache
  • flushing of the skin
  • profuse sweating, particularly on the forehead
  • lightheadedness, dizziness, or confusion
  • dilated pupils

How Is Autonomic Dysreflexia Diagnosed?

Because AD requires immediate medical response, the condition is generally treated on the spot. Treatment is based on the presenting symptoms as well as pulse and blood pressure readings. Once the immediate emergency has passed, your doctor will probably want to do a thorough examination and run diagnostic tests. This is done to determine the exact cause of the overreaction and to rule out any other potential underlying causes.

How Is Autonomic Dysreflexia Treated?

Emergency response is aimed at lowering the blood pressure and eliminating the stimuli that are triggering the reaction. Emergency measures may include:

  • placing the patient in a sitting position to cause the blood to flow to the feet
  • removing tight clothes and socks
  • checking for a blocked catheter
  • draining the bladder with a catheter if it is distended
  • removing any other potential triggers such as drafts of air blowing on the patient or objects touching the skin
  • treating the patient for fecal impaction
  • administering vasodilators or other drugs to bring the blood pressure under control

Can Autonomic Dysreflexia Be Prevented?

Long-term treatment and prevention are aimed at identifying and addressing the underlying issues that trigger AD. A long-term treatment plan might include:

  • changes in medication or diet to improve elimination
  • improved management of urinary catheters
  • medications for high blood pressure
  • medications or a pacemaker to stabilize the heartbeat
  • self-management to avoid triggers

What Is the Prognosis for Autonomic Dysreflexia?

If the triggers for AD can be managed, the prognosis is good. If the condition is due to unknown causes or conditions that are hard to control, the prognosis is more uncertain. Repeated episodes of uncontrolled spikes or drops in blood pressure can result in strokes or cardiac arrest.

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