Autonomic Dysreflexia: Symptoms, Types, Causes and Treatment

Autonomic dysreflexia (AD) is a serious, potentially life-threatening condition that can develop after a spinal cord injury (SCI), especially in those with injuries at or above the level of the sixth thoracic vertebra (T6). While some people may not experience symptoms, others can face sudden, severe health emergencies. Understanding the symptoms, types, causes, and treatments of AD is essential for patients, caregivers, and clinicians. This comprehensive guide delves into each area, providing clear explanations and evidence-based insights.

Symptoms of Autonomic Dysreflexia

Autonomic dysreflexia can strike suddenly, and recognizing its symptoms early is crucial for preventing dangerous complications. People living with SCI, their families, and health professionals should be vigilant for the warning signs—some of which may appear subtle, while others are dramatic and unmistakable.

Symptom	Description	Severity	Source(s)
Hypertension	Sudden increase in systolic BP (≥25 mm Hg)	Life-threatening	3 4 5 9
Headache	Throbbing, pounding pain	Common, severe	3 4 5 9
Flushing	Redness above injury	Moderate	3 4 5
Sweating	Profuse, above level of injury	Moderate	3 4 5 9
Bradycardia	Slowed heart rate	Can be severe	3 4 5 9
Anxiety	Sense of dread or unease	Mild to severe	3 4 5
Nasal congestion	Blocked/runny nose	Mild to moderate	3 4
Goosebumps	Piloerection, often below injury	Mild	3 5
Nausea	Feeling sick	Variable	3 5
Blurred vision	Loss of clear sight	Moderate	3 4

Table 1: Key Symptoms

Sudden and Severe Blood Pressure Changes

The hallmark of AD is a rapid and significant rise in systolic blood pressure, often defined as an increase of 25 mm Hg or more above baseline. This is especially concerning because people with high-level SCI often have low resting blood pressure, so even moderate-seeming elevations can be dangerous. If not recognized and treated, severe hypertension can lead to stroke, seizures, retinal hemorrhage, or even death 3 4 5 9 12.

Headache and Flushing

A pounding, throbbing headache is one of the most common complaints during an AD episode. This is often accompanied by facial flushing and sweating above the level of the spinal injury. These symptoms are caused by the body's attempt to counteract the sudden increase in sympathetic activity 3 4 5.

Other Autonomic Signs

Bradycardia, or a slowed heart rate, frequently follows the hypertensive episode as a reflex response. Patients may also experience anxiety, nasal congestion, goosebumps (piloerection), nausea, and blurred vision. The combination and severity of these symptoms can vary. Notably, some people may have only mild symptoms or even none at all, making vigilance especially important 3 4 5 9.

Variability and Recognition

Up to 90% of individuals with cervical or upper thoracic injuries (above T6) may experience some degree of AD, though not all are symptomatic 4. Incomplete injuries are less likely to result in full-blown episodes, but partial symptoms may still appear 1 9. Because symptoms can be mistaken for other problems, or go unnoticed due to the patient’s sensory deficits, it's essential to maintain a high index of suspicion in at-risk individuals.

Types of Autonomic Dysreflexia

Autonomic dysreflexia is often discussed as a single condition, but its presentation and triggers can vary widely. Understanding these differences can help with rapid recognition and appropriate management.

Type	Trigger Nature	Frequency	Source(s)
Acute	Sudden, intense	Common	3 6 14
Chronic	Ongoing triggers	Less common	8 14
Complete SCI	Total loss below T6	More prevalent	1 9
Incomplete SCI	Partial loss	Less prevalent	1 9

Table 2: Types of Autonomic Dysreflexia

Acute vs. Chronic Episodes

• Acute AD: These are sudden, short-lived episodes triggered by a specific stimulus, such as bladder distention or skin irritation. Acute episodes are medical emergencies and require immediate intervention to prevent complications 3 6 14.
• Chronic AD: In some cases, particularly if triggers are not addressed, patients may experience ongoing, lower-grade symptoms, or repeated episodes over time. Chronic AD is less common but can severely impact quality of life 8 14.

Complete vs. Incomplete Spinal Cord Injury

• Complete SCI: Individuals with complete spinal cord injury above T6 are at the highest risk for AD. Studies show that up to 91% of individuals with complete tetraplegia experience AD 1 9.
• Incomplete SCI: The risk and severity of AD are much lower in those with incomplete injuries, with approximately 27% affected 1 9. Symptoms are often less intense.

Noxious vs. Innocuous Triggers

AD can be induced by both painful (noxious) and non-painful (innocuous) stimuli below the level of injury. The response to these triggers may vary in intensity, but both types can provoke dangerous episodes 7.

Causes of Autonomic Dysreflexia

Understanding the underlying causes of AD is essential for both prevention and effective management. Most episodes are triggered by stimuli below the level of the spinal cord injury, leading to an exaggerated sympathetic response.

Cause	Description	Frequency	Source(s)
Bladder issues	Distension, infection, blocked catheter	Most common	3 6 8 12
Bowel issues	Constipation, impaction, rectal exams	Very common	3 8 12
Skin stimuli	Pressure sores, tight clothing, burns	Common	3 6 8
Other triggers	Fractures, sexual activity, procedures	Less common	3 6 8
Underlying mechanism	Loss of supraspinal control, reflex hyperactivity	Universal	1 5 10 11

Table 3: Common Causes

Bladder-Related Triggers

Bladder distension—often due to a blocked catheter, urinary retention, or infection—is the leading cause of AD. Any irritation of the lower urinary tract can set off a dangerous cascade of sympathetic nervous system activity 3 6 8 12.

Bowel-Related Triggers

Constipation, fecal impaction, manual evacuation, or even routine rectal examinations can provoke AD. The bowel is richly innervated and highly sensitive after spinal cord injury, making it a frequent culprit 3 8 12.

Skin and Other Triggers

Other common triggers include skin irritation (such as pressure sores, burns, or ingrown toenails), tight clothing, or even less obvious events like bone fractures or sexual activity. Any stimulus, even those that would be considered minor in able-bodied individuals, can spark a severe episode 3 6 8.

Pathophysiology: Disconnection and Reflexes

The root cause of AD is the loss of supraspinal (brain) control over the sympathetic spinal centers below the level of injury. With this control lost, sensory input from below the lesion triggers unmodulated reflex sympathetic hyperactivity, causing vasoconstriction and hypertension. The brain attempts to counteract this by slowing the heart rate, but the descending inhibitory signals cannot reach the lower body due to the injury 1 5 10 11.

Neurophysiological and Structural Changes

Research indicates that after SCI, there is plasticity within the spinal cord, including nerve growth factor (NGF)-dependent sprouting of afferent fibers, which amplifies the reflex response. Treatments that block NGF or limit secondary damage may reduce the risk and severity of AD by preserving white matter and limiting abnormal sprouting 10 11 16.

Treatment of Autonomic Dysreflexia

Prompt and effective management of AD can be lifesaving. Both immediate and long-term strategies are needed, focusing on removing triggers, symptomatic control, and prevention.

Step/Modality	Description	Evidence Level	Source(s)
Remove stimuli	Address bladder/bowel/skin triggers	Consensus	3 6 13 14
Positioning	Sit upright to lower BP	Consensus	13 14
Loosen clothing	Remove constricting garments	Consensus	13 14
Antihypertensives	Nifedipine, prazosin, terazosin, others	RCTs/observational	13 14 15
Prevention	Regular bladder/bowel care, skin checks	Observational	3 5 13
Patient education	Emergency cards, ‘AD kits’	Consensus	3 14
Experimental	Anti-NGF, anti-CD11d, neuroprotectives	Preclinical	10 11 16

Table 4: Treatment Strategies

Immediate Management

• Remove the trigger: The first and most crucial step is to identify and eliminate the offending stimulus—empty the bladder, check the catheter, relieve bowel impaction, or address skin irritation 3 6 13 14.
• Position the patient upright: Sitting the person up helps reduce blood pressure via gravity 13 14.
• Loosen tight clothing: Remove anything constricting to reduce any additional stimuli 13 14.

Pharmacological Intervention

If symptoms do not resolve rapidly, or if blood pressure remains dangerously elevated, antihypertensive medications are indicated:

• Nifedipine: A fast-acting calcium channel blocker, often used sublingually for acute episodes 13 14.
• Prazosin/Terazosin: Alpha-blockers that can be used for prevention or ongoing management 13 14 15.
• Other agents: Phenoxybenzamine, nitrates, and mecamylamine are alternatives, depending on clinical context 14.
• Terazosin has shown efficacy in reducing AD severity and frequency without significant side effects 15.

Prevention and Long-Term Strategies

• Bladder and bowel care: Regular, scheduled emptying and monitoring to prevent distension and impaction 3 5 13.
• Skin care: Frequent checks for pressure sores, burns, or other injuries 3 5.
• Emergency preparedness: Individuals at risk should carry medical emergency cards and ‘AD kits’ containing useful items such as catheters and prescribed medications 3 14.
• Education: Teaching patients, caregivers, and healthcare providers about AD recognition and response is critical 3 14.

Emerging and Experimental Treatments

Preclinical studies suggest that treatments targeting nerve growth factor (NGF) or inflammatory pathways (such as anti-CD11d antibodies) can reduce abnormal nerve sprouting and the severity of AD. Early neuroprotective interventions may prevent the development of AD after SCI, but these remain experimental at present 10 11 16.

Conclusion

Autonomic dysreflexia is a complex, potentially life-threatening condition that affects many people with spinal cord injuries above T6. Prompt recognition, prevention, and management are vital for safety and quality of life. Here’s a summary of the main points covered:

• Symptoms: Sudden hypertension, headache, flushing, sweating, bradycardia, and other autonomic signs are key indicators.
• Types: Acute (sudden onset) and chronic (ongoing), with risk higher in complete SCI and those injured above T6.
• Causes: Most often due to bladder or bowel irritation, but any stimulus below the injury can trigger an episode.
• Treatment: Immediate removal of the trigger, patient positioning, antihypertensive medications, and long-term prevention strategies. Education and preparedness are essential.
• Emerging therapies: Targeting neuroplasticity and inflammation in the spinal cord may offer future hope.

By staying vigilant and informed, patients and caregivers can prevent complications and improve outcomes for those living with spinal cord injuries.