What Is Autonomic Dysreflexia? Warning Signs, Triggers, and What to Do
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick Answer: What is autonomic dysreflexia?
Autonomic dysreflexia (AD) is a dangerous syndrome in which the nervous system overreacts to a stimulus below a spinal cord injury, usually at or above T6, spiking blood pressure. [1] [3] A severe headache is typically the first sign, and bladder blockages cause up to 85% of episodes. [1] Sit the person upright and remove the trigger; persistent high pressure needs emergency care. [1]
Key Takeaways
Autonomic dysreflexia (AD) is an overreaction of the autonomic nervous system that causes sudden, severe high blood pressure. [1]
It most often affects people with a spinal cord injury at or above the T6 vertebra; up to 90% of people with cervical or high-thoracic injuries are susceptible. [1]
A severe, throbbing headache is usually the first symptom, along with sweating and flushing above the injury level and pale, cold skin below it. [1]
Bladder problems trigger up to 85% of episodes, followed by bowel issues and skin irritants. [1]
The first response is to sit upright with legs dangling and remove tight clothing or constrictive devices. [1]
Most episodes stop once the trigger is removed; if not, emergency treatment with rapid-acting blood pressure medication is needed. [1]
With quick recognition and treatment, the prognosis is usually good, but untreated severe cases can lead to stroke or worse. [1]
What the research says
Bladder procedures are a frequent trigger, so blood pressure should be watched. A systematic review of 40 studies found that AD occurred in 36.7% to 77.8% of people with spinal cord injury during urodynamic testing, and was more common in cervical than thoracic injuries; the authors recommend routine blood pressure monitoring during urological procedures. (Liu et al., Spinal Cord, 2015) [2]
AD is a reflex that loses its brake after injury at or above T6. A review defines AD as episodic high blood pressure with a slow heart rate (baroreflex-mediated bradycardia), set off by noxious but unperceived stimuli below the injury, and notes that severe episodes can require immediate medical attention. (Eldahan and Rabchevsky, Auton Neurosci, 2017) [3]
Prevention research is still early and so far in animals. In rodent spinal cord injury models, transplanting embryonic presympathetic neurons reduced spontaneous AD and the severity of triggered episodes, though baroreflex dysfunction persisted. (Trueblood et al., Neuroscientist, 2024) [4]
What Is Autonomic Dysreflexia?
Autonomic dysreflexia (AD) is a potentially life-threatening syndrome involving an abnormal, exaggerated response of the autonomic nervous system to painful sensory input. It most often happens after a spinal cord injury at or above the sixth thoracic vertebra (T6). [1]
The thoracic spine is the middle section of the spine, running from the base of the neck to the bottom of the ribs. It is the longest section and contains 12 vertebrae, labeled T1 through T12. [1]
The main sign of AD is sudden and severe high blood pressure, and the main symptom is a headache. Most cases first occur two to three months after the spinal cord injury, once spinal shock and neurogenic shock have resolved. [1]
A person with AD usually has more than one episode in their lifetime, and susceptible individuals can experience up to 40 episodes in a single day. [1]
You may also see AD referred to by other names, including autonomic hyperreflexia, hypertensive autonomic crisis, sympathetic hyperreflexia, autonomic spasticity, paroxysmal hypertension, mass reflex, and viscero-autonomic stress syndrome. [1]
How Does Autonomic Dysreflexia Happen?
The autonomic nervous system controls automatic functions needed to survive, including heart rate, blood pressure, breathing, and digestion. [1] It has three divisions:
Division | Job |
Sympathetic nervous system (SNS) | Activates “fight-or-flight” processes during stress or danger |
Parasympathetic nervous system (PNS) | Controls “rest and digest” processes; opposes the SNS |
Enteric nervous system (ENS) | Manages how the body digests food |
During an AD episode, the body senses a painful or damaging stimulus below the injured spinal cord. This provokes a sympathetic nervous system reflex, as if the body were in danger. The result is widespread vasoconstriction — narrowing of blood vessels — in the lower body, which drives up blood pressure. [1]
Normally, a mechanism called the baroreflex would correct that pressure spike. The brain responds by slowing the heart and sending signals down the spinal cord to relax blood vessels and bring pressure down. But with an injured spinal cord, the parasympathetic response cannot travel below the lesion. Only the upper body experiences vasodilation, while vasoconstriction continues in the lower body — leading to dangerously high blood pressure. [1]
This mismatch also explains why the skin looks different above and below the injury. The skin above the injury level, such as the face, neck, and arms, becomes redder and sweaty. The skin below the injury level, such as the lower torso and legs, becomes pale, cold, and dry. [1]
Who Gets Autonomic Dysreflexia?
AD most often affects people who have had a spinal cord injury at or above the T6 level, though not everyone with this injury develops it. Most spinal cord injuries come from a sudden, traumatic blow that fractures vertebrae, compressing blood flow to the spinal cord and damaging the cord and nearby nerves. In rare cases, the injury completely severs the spinal cord. [1]
The higher the level of the injury, and the more complete the damage, the greater the risk of AD. [1] Up to 90% of people with cervical (neck) or high-thoracic spinal cord injuries are susceptible to the condition. [1]
Women who are pregnant and have a spinal cord injury at T6 or higher are especially at risk of an AD episode during labor and delivery. [1]
Statistic | Detail |
Annual spinal cord injuries in the U.S. | About 17,000 per year |
Most common injury regions | Cervical (neck) and thoracic — the regions that make AD most likely |
AD development rate | 48% to 70% of people with a spinal cord injury above T6 |
Susceptibility at high levels | Up to 90% of people with cervical or high-thoracic injuries |
Possible episodes | Up to 40 episodes per day in susceptible people |
What Are the Symptoms of Autonomic Dysreflexia?
Autonomic dysreflexia symptoms vary and usually begin suddenly. The first symptom is typically a severe headache that many people describe as throbbing, caused by the sudden and severe jump in blood pressure. [1]
AD can also cause the following symptoms:
Symptom | What It May Look Like |
Throbbing headache | Often the very first symptom, from the blood pressure spike |
Excessive sweating | Sweating above the level of the spinal injury |
Slow heart rate (bradycardia) | Heart beating slower than normal |
Skin flushing | Redder skin above the injury; dry, pale skin below it |
Goosebumps | Above the level of the spinal cord injury |
Cold skin | Often felt below the injury level |
Stuffy nose | Nasal congestion during the episode |
Nausea and vomiting | Upset stomach during the episode |
Blurred vision | Difficulty seeing clearly |
Feelings of anxiety or doom | An intense, unexplained sense that something is wrong |
If you are experiencing these symptoms, get medical help as soon as possible.
What Causes Autonomic Dysreflexia?
The most common cause of AD is a spinal cord injury. [1] In people with AD, the sympathetic and autonomic nervous systems over-respond to certain types of stimulation.
Typically, a noxious stimulus below the level of the injury triggers a massive sympathetic reflex that narrows blood vessels throughout the lower body. A noxious stimulus is anything that is actually or potentially damaging tissue — something likely to cause pain, even if pain is not actually felt. It could be anything from an itch that cannot be scratched to an overly full bladder. [1]
Other conditions can make someone susceptible to AD, though episodes are much less likely with these causes: [1]
Other Possible Cause | Description |
Intramedullary astrocytoma | A central nervous system tumor |
Multiple sclerosis (MS) | A disease affecting the central nervous system |
Guillain-Barré syndrome | A condition affecting peripheral nerves |
Medication side effects | Reactions to some drugs |
Severe head trauma | Serious brain injuries |
Subarachnoid hemorrhage (SAH) | Bleeding around the brain |
Illegal stimulant drugs | Such as cocaine and amphetamines |
What Triggers an Autonomic Dysreflexia Episode?
The most common noxious stimuli that trigger AD involve the bladder, the bowel, and the skin. [1] Knowing all the possible triggers matters for people at risk, so they can prevent them or fix them quickly when symptoms appear.
Bladder Triggers (Most Common)
Bladder issues are the number one trigger of AD, responsible for up to 85% of cases. [1] Most often, something blocks urine from passing out of the body, leaving the bladder overly full. This is frequently an issue with a urinary catheter, such as a kink or a clog, but can also come from bladder spasms, bladder stones, or urinary tract infections. [1]
Bowel Triggers (Second Most Common)
An over-stretched bowel is the second most common trigger. [1] Causes include quick movement, fecal impaction, constipation, gas and gas pain, enemas, and manual removal of stool. Other bowel irritants that can trigger AD include diarrhea, diverticulitis, Crohn’s disease, anal fissures, and hemorrhoids. [1]
Skin Triggers (Third Most Common)
Skin problems round out the top three. Possible triggers include pressure injuries (bedsores), cuts or bruises, rashes, clothing that is too tight, lumpy, or baggy, an itch that cannot be sensed or scratched, and ingrown toenails. [1]
Trigger Category | Examples |
Bladder (up to 85% of cases) | Blocked catheter, bladder distension, spasms, stones, UTIs, bladder procedures |
Bowel (second most common) | Fecal impaction, constipation, gas pain, enemas, diarrhea, Crohn’s disease, hemorrhoids |
Skin (third most common) | Bedsores, cuts, rashes, tight clothing, unsensed itches, ingrown toenails |
How Is Autonomic Dysreflexia Diagnosed?
There is no single test that can diagnose AD. [1] Healthcare providers and caregivers largely base the diagnosis on three things:
Diagnostic Element | What Providers Look For |
Medical history | Especially a history of spinal cord injury |
Blood pressure | A rise in systolic blood pressure of more than 20 to 40 mmHg above the person’s usual baseline is usually considered a sign of AD |
Symptoms | Especially a severe headache |
If someone has symptoms of AD but has never had a spinal cord injury, the provider will perform a complete nervous system and medical examination. [1] They may order additional tests to find the underlying cause:
Possible Test | What It Checks |
Blood and urine tests | General health and infection signs |
CT or MRI scan | Imaging of the brain and spine |
Electrocardiogram (EKG) | Heart electrical activity |
Spinal tap (lumbar puncture) | Fluid around the spinal cord |
Tilt-table test | How blood pressure responds to position changes |
Drug testing | Presence of stimulants or other substances |
X-rays | Bone and structural findings |
How Is Autonomic Dysreflexia Treated?
The first step of treatment is to sit the person upright with their legs dangling and remove any tight clothing or constrictive devices. [1] This helps lower blood pressure right away. [1]
Most episodes go away once the trigger is removed. [1] So the next step is to identify and eliminate the trigger, if possible, before reaching for medication or medical procedures. Common trigger checks include:
First-Response Step | Purpose |
Sit upright with legs dangling | Helps lower blood pressure immediately |
Remove tight clothing or constrictive devices | Eliminates pressure that sustains the spike |
Check and restore bladder drainage | Fixes the most common trigger — a blocked or overfull bladder |
Evaluate a Foley catheter for blockage or malfunction | Catheter kinks and clogs are a frequent cause |
Test a urine sample for infection | UTIs are treated with antibiotics if found |
Check for fecal impaction | A rectal exam evaluates the second most common trigger |
People with a history of autonomic dysreflexia are usually very knowledgeable about the condition and are prepared to implement a treatment plan themselves. [1]
If the trigger cannot be found and initial steps do not improve blood pressure, emergency treatment is necessary. Call 911 (or your local emergency number) or get immediate medical help. Providers use rapid-acting drugs such as nitrates, hydralazine, labetalol, or nifedipine to bring blood pressure down, while monitoring vital signs closely. Tell the care team if you have taken an erectile dysfunction medicine such as sildenafil in the past day or two, because nitrates must not be given with these drugs. [1]
What Is the Prognosis for Autonomic Dysreflexia?
The prognosis is usually good as long as the episode is recognized quickly, emergency treatment starts promptly, the person and their caregivers are properly educated about the signs and triggers, and proper precautions are taken to prevent episodes. [1]
Severe cases that do not receive rapid, appropriate treatment can have serious consequences, including hypertensive encephalopathy, stroke, cardiac arrest, seizure, and death. Fortunately, death from AD is rare. [1]
How Can I Take Care of Myself If I’m at Risk?
People at risk for AD and their loved ones need to be actively involved in identifying episodes. The moment symptoms start, begin treatment by sitting up. Call for assistance so you do not fall, get hurt, or lose consciousness. [1] Someone should call 911 if the trigger cannot be found or if the treatment steps are not working.
It is also important to carry an emergency treatment pack with any prescribed treatment therapies and information explaining autonomic dysreflexia, so that someone unfamiliar with AD can help. [1]
If you have had episodes of AD, let all of your healthcare providers, caregivers, and loved ones know about your condition in case it happens again and you do not have time to call for help. [1]
Can Autonomic Dysreflexia Be Prevented?
It is not always possible to prevent autonomic dysreflexia. But if you have a spinal cord injury, especially at or above the T6 level, several habits can help: [1]
Prevention Habit | How It Helps |
Empty the bladder regularly | Prevents the overfull bladder that triggers up to 85% of episodes |
Manage pain | Reduces noxious stimuli that provoke the reflex |
Practice proper bowel care | Avoids fecal impaction and constipation |
Practice proper skin care | Prevents pressure sores and skin infections |
Prevent urinary tract infections | Removes another common bladder trigger |
Conclusion
Autonomic dysreflexia (AD) is a serious syndrome in which the autonomic nervous system overreacts to a stimulus below a spinal cord injury, driving blood pressure to dangerous levels in moments. [1] It most often affects people with injuries at or above the T6 vertebra, and a sudden throbbing headache is usually the first warning. [1] Bladder problems cause up to 85% of episodes, followed by bowel and skin triggers — which is why recognizing and removing the trigger is the heart of treatment. [1]
Sitting upright with legs dangling is the first move, followed by checking the bladder, bowel, and skin for the cause. [1] If blood pressure does not come down, emergency care with rapid-acting medication is essential. [1] With quick recognition and the right response, the prognosis is usually good. [1] If you are at risk, share this knowledge with everyone around you.
Frequently Asked Questions
What is autonomic dysreflexia in simple terms?
Autonomic dysreflexia (AD) is a medical emergency in which the body’s automatic nervous system overreacts to a painful stimulus below a spinal cord injury, causing blood pressure to spike to dangerously high levels. [1] It most often affects people with injuries at or above the T6 vertebra. [1]
What does autonomic dysreflexia feel like?
The first symptom is usually a severe, throbbing headache caused by the sudden blood pressure spike. [1] People may also experience heavy sweating and flushed skin above the injury level, cold and pale skin below it, a slow heart rate, goosebumps, a stuffy nose, nausea, blurred vision, and an intense feeling of anxiety or doom. [1]
Why is autonomic dysreflexia dangerous?
Because it causes sudden, severe high blood pressure that can damage the brain and heart if not treated quickly. [1] Untreated severe cases can lead to stroke, cardiac arrest, seizures, and in rare cases, death. [1]
What triggers autonomic dysreflexia?
The most common triggers are bladder problems, responsible for up to 85% of episodes — especially a blocked catheter or an overfull bladder. [1] Bowel issues such as constipation and fecal impaction come second, and skin irritants such as bedsores, tight clothing, or ingrown toenails come third. [1]
How is autonomic dysreflexia treated in the moment?
The first step is to sit the person upright with their legs dangling and remove any tight clothing or constrictive devices. [1] Then the trigger should be found and removed — often by checking the bladder and catheter, testing for a urinary infection, or checking for fecal impaction. [1] Most episodes resolve once the trigger is gone. [1]
When should I call 911 for autonomic dysreflexia?
Call 911 or get immediate emergency help if the trigger cannot be found and the person’s blood pressure does not improve after sitting upright and checking the bladder, bowel, and skin. [1]
Can autonomic dysreflexia be prevented?
Not always, but regular bladder emptying, pain management, good bowel care, careful skin care, and preventing urinary tract infections can all reduce the risk of episodes. [1]
Is autonomic dysreflexia a lifelong condition?
People with AD typically experience more than one episode in their lifetime, and susceptible individuals can have many episodes — sometimes up to 40 in a single day. [1] Education and preparation help people manage episodes quickly when they occur.
How is autonomic dysreflexia diagnosed?
There is no single diagnostic test. Providers base the diagnosis on the person’s history of spinal cord injury, their symptoms (especially a severe headache), and a rise in systolic blood pressure of more than 20 to 40 mmHg above the person’s usual baseline. [1]
Can pregnant women with spinal cord injury have autonomic dysreflexia?
Yes. Women who are pregnant and have a spinal cord injury at T6 or above are at especially high risk of an AD episode during labor and delivery. [1]
Who is most at risk for autonomic dysreflexia?
People with a spinal cord injury at or above the sixth thoracic vertebra (T6). [1] Up to 90% of people with cervical or high-thoracic spinal cord injuries are susceptible, and AD develops in 48% to 70% of people with injuries above T6. [1]
What should I tell my loved ones about autonomic dysreflexia?
Everyone around a person at risk should know the warning signs, the first steps (sit upright, legs dangling, loosen tight clothing), the common triggers, and when to call 911. Carrying an emergency pack with prescribed therapies and information about AD helps unfamiliar helpers act quickly. [1]
Related Reading
References
Cleveland Clinic. Autonomic Dysreflexia (AD). Cleveland Clinic Health Library. Last updated October 27, 2022. https://my.clevelandclinic.org/health/diseases/24378-autonomic-dysreflexia-ad
Liu N, Zhou M, Biering-Sørensen F, Krassioukov AV. Iatrogenic urological triggers of autonomic dysreflexia: a systematic review. Spinal Cord. 2015;53(7):500-509. PMID 25800696. https://doi.org/10.1038/sc.2015.39
Eldahan KC, Rabchevsky AG. Autonomic dysreflexia after spinal cord injury: systemic pathophysiology and methods of management. Auton Neurosci. 2017;209:59-70. PMID 28506502. https://doi.org/10.1016/j.autneu.2017.05.002
Trueblood CT, Singh A, Cusimano MA, Hou S. Autonomic dysreflexia in spinal cord injury: mechanisms and prospective therapeutic targets. Neuroscientist. 2024;30(5):597-611. PMID 38084412. https://doi.org/10.1177/10738584231217455
Medical disclaimer
This article is for informational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider for diagnosis and treatment.
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