Autonomic dysreflexia
A life-threatening hypertensive emergency in spinal cord injury patients.
Autonomic dysreflexia (AD), also called autonomic hyperreflexia, is a life-threatening medical emergency marked by dangerously high blood pressure and abnormal heart rhythms. It most often affects people with spinal cord injuries, especially those with damage at or above the T6 vertebra, though cases have been reported with injuries as low as T10. Guillain-Barré syndrome can also trigger this condition.
The condition is distinct and typically occurs in episodes. A rise of 20 mm Hg or more above a person’s baseline systolic blood pressure, along with a possible trigger below the level of the spinal injury, meets the current definition. Common symptoms include headache, sweating, facial redness, goosebumps, nasal stuffiness, blurred vision, and a sense of doom or apprehension. Mild hypertension may cause sweating above the injury level, goosebumps, blurred vision, or headache. Severe hypertension can lead to seizures, stroke from bleeding in the brain, heart attack, or retinal detachment.
Both painful and non-painful stimuli can set off an episode. The trigger causes a surge of sympathetic nervous system activity. This surge travels through intact peripheral nerves, leading to widespread narrowing of blood vessels below the spinal injury. The resulting high blood pressure activates baroreceptors, which trigger a parasympathetic response from the central nervous system to calm the sympathetic outflow. However, this parasympathetic signal cannot travel past the spinal lesion to lower the blood pressure. This leads to bradycardia or tachycardia, flushing, pupil constriction, and nasal stuffiness above the injury, while below the injury the skin becomes pale, cool, and develops goosebumps due to ongoing sympathetic activity.
The most common triggers are bladder or bowel overdistension from urinary retention or fecal impaction. Other causes include pressure sores, extreme temperatures, fractures, unnoticed painful stimuli (like a pebble in a shoe), startle reflex, stomach distension, sexual activity, and severe spinal cord pain. The first episode can occur weeks to years after the spinal injury, usually once reflexes return after spinal shock. Most people at risk have their first episode within the first year. Not all painful stimuli cause AD—some, like broken bones, may not trigger it and might even go unnoticed. Recurrent episodes without an obvious cause can
- field
- Medical emergency
- known_for
- Life-threatening hypertension and cardiac arrhythmias in spinal cord injury patients
- primary_cause
- Noxious stimuli below the level of spinal cord lesion, most commonly bladder or bowel over-distension
- key_symptom
- Elevation of 20 mm Hg over baseline systolic blood pressure
- treatment
- Removing or correcting the noxious stimuli, sitting patient upright, and fast-acting antihypertensives if systolic remains over 150 mm Hg
Lore & Background
Autonomic dysreflexia (AD) is a distinct, usually episodic condition that arises from hyperactivity of the sympathetic nervous system triggered by noxious or non-noxious stimuli below the level of a spinal cord lesion. The most common triggers include bladder or bowel over-distension from urinary retention and fecal compaction, as well as pressure sores, extreme temperatures, fractures, undetected painful stimuli, startle reflex, gastric distension, sexual activity, and extreme spinal cord pain. The first episode may occur weeks to years after the spinal cord injury, typically after reflexes have returned following spinal shock, and most at-risk individuals develop their first episode within the first year after injury.
Reader's Guide
Autonomic dysreflexia is significant as a medical emergency that requires immediate recognition and intervention to prevent life-threatening complications such as seizure, intracranial bleeds (stroke), myocardial infarction, pulmonary edema, and retinal detachment. The mechanism involves interruption of descending autonomic pathways at the spinal cord lesion, leading to abnormal reflex activation of sympathetic preganglionic neurons and systemic vasoconstriction below the lesion. Treatment focuses on removing the triggering stimulus—such as catheterizing the bladder or disimpacting the bowel—and, if systolic blood pressure remains above 150 mm Hg, administering fast-acting short-duration antihypertensives. Prognosis is generally good and mortality rare when the trigger is identified and managed. Education of patients, families, and caregivers about avoidance of triggers, along with routine bladder and bowel programs and urological follow-up, is important for prevention.
Did You Know?
- Autonomic dysreflexia is sometimes referred to as autonomic hyperreflexia.
- Most cases occur in individuals with spinal cord injuries, with lesions at or above T6 most frequently reported.
- The most common cause is bladder or bowel over-distension from urinary retention and fecal compaction.
- An elevation of 20 mm Hg over baseline systolic blood pressure meets the current definition of dysreflexia.
Frequently Asked Questions
Who is Autonomic dysreflexia?
Autonomic dysreflexia is a sudden, life-threatening medical emergency defined by a sharp spike in blood pressure and irregular heart rhythms. It primarily strikes individuals who have sustained spinal cord damage at or above the T6 level, though it has also been linked to Guillain-Barré syndrome.
What are Autonomic dysreflexia's powers/effects?
Its signature move is pushing systolic blood pressure at least 20 mm Hg above the patient's normal baseline, often accompanied by dangerous cardiac arrhythmias. Episodes come in discrete waves rather than persisting continuously, which makes them both unpredictable and acutely severe.
What triggers Autonomic dysreflexia?
The condition is set off by any irritating stimulus located below the level of the spinal cord lesion, with an overfilled bladder or distended bowel being the most common culprits. Other noxious inputs such as tight clothing, pressure sores, or surgical procedures can also ignite an episode.
How do you treat or defeat Autonomic dysreflexia?
The first line of defense is identifying and removing the offending stimulus while positioning the patient upright so blood pools in the lower extremities. If systolic pressure remains above 150 mm Hg after those steps, fast-acting antihypertensive medications are administered to bring the dangerous reading down.
Why is Autonomic dysreflexia important?
It is classified as a true medical emergency because untreated hypertensive episodes can escalate into seizures, stroke, or cardiac arrest. Its significance lies in the fact that spinal cord injury patients often cannot feel the triggering stimulus below their lesion, making rapid recognition and intervention critical to survival.
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