Of the 300,000 Americans living with spinal cord injuries today, 20.4% are complete tetraplegia and 25.6% complete paraplegia, according to a Medscape article.

Researchers attribute spinal cord injury almost entirely to trauma. Non-traumatic causes, such as medical (iatrogenic), pathological and congenital causes, however, represent a small percentage that increases with age.

Specific data regarding the prevalence of non-traumatic spinal cord injury was conspicuously lacking in the literature. Despite this setback, estimates range from 11.4 per million to 26 per million worldwide. However, these figures vary greatly from country to country, region to region and study to study. The World Health Organization had no concrete data on the global incidence and prevalence of non-traumatic spinal cord injury.

The total number of complete tetraplegic individuals, on the other hand, proved fairly specific at slightly more than 20%. Additionally, they found that 25% of individuals suffer from complete paraplegia. Again, numbers vary with different studies, but remain within a close range overall.

No clear number was given in the latter group as to the level of spinal cord injury, so it is hard to state with certainty the number of paraplegic patients with T6 or higher lesions. The actual number is probably less than the 25.6% stated earlier.

The incidence of incomplete tetraplegic and paraplegic individuals came to 30.1% and 23.9%, respectively. Again, there was no breakdown as to the level of spinal cord injury in the paraplegic group. Thus, the actual number for T6 or higher insult is probably less than 23.9%. Tetraplegic implies an injury above T6 (so we see 100% T6 or higher in this group, as with complete tetraplegic group), most often at the cervical level, according to the article “Prevalence of Autonomic Dysreflexia in Patients With Spinal Cord Injury Above T6” from BioMed Research International.

What this means for autonomic dysreflexia

The level of spinal cord injury is relevant as the incidence of autonomic dysreflexia is between 48% to 90% in patients with T6 or higher spinal cord injuries. It has been reported rarely with spinal cord injury as low as T10, according to the article “Cerebral Hemorrhage Due to Autonomic Dysreflexia in a Spinal Cord Injury Patient” published in the journal Spinal Cord.

Patients who sustain complete, as opposed to partial, transection prove much more likely to experience autonomic dysreflexia — 91% compared to 27%, respectively, according to a Medscape article. Specific numbers and percentages vary with various authors and studies, but these seemed to represent a general consensus among them.

The pathophysiology of autonomic dysreflexia appears to be a profound onset of sympathetic stimulation below the spinal cord injury level. This involves spinal reflexes unopposed by corresponding parasympathetic stimulation traveling from the central nervous system via the spinal cord. Skeletal muscles as well as the splenic and mesenteric vascular beds take part in this process.

Common symptoms of autonomic dysreflexia

autonomic dysflexiaQuite often the stimulus is a noxious — commonly bowel and bladder — issue, though this is not always the case. According to the article “What Is Autonomic Dysreflexia?” on WebMD, the stimulus can be slight or even pleasurable, massage or sexual stimulation. Something as mild as a cool breeze, bedding touching below the spinal cord injury or even tight clothing.

Similarly, spontaneous episodes can occur without an identifiable stimulus at all. Such stimulation goes unnoticed by the patient, and the first inkling of trouble is the onset of symptoms.

The phenomenon develops post-spinal cord injury and after the resolution of associated spinal shock, following the return of the spinal reflexes, according to Medscape. The mechanism by which autonomic dysreflexia occurs is a stimulus below the level of the spinal cord injury that provokes a sympathetic response via the now intact spinal reflexes.

The response incurs mass vasoconstriction below the spinal cord injury, such as a sympathetic response. Sensory signals of increased blood pressure from the carotid bodies reach the central nervous system. This then sends an opposing parasympathetic signal back along the spinal cord. However, it cannot pass the spinal cord lesion.

The result is unopposed sympathetic tone below the spinal cord injury and massive parasympathetic tone above, according to the article, “Autonomic Dysreflexia in Spinal Cord Injury Patients: An Overview,” which was published in The Journal of the Canadian Chiropractic Association.

The resultant clinical picture presents as:

  • Flushing of the face and upper body (area above the spinal cord injury)
  • Pupil dilation
  • Nasal congestion (parasympathetic response)
  • Profuse diaphoresis
  • Blurred vision
  • Headache
  • Piloerection
  • Elevated blood pressure (sympathetic response)

Elevated blood pressure is a serious concern

The elevated blood pressure does not remain confined to the area below the spinal cord injury. Rather, it is systemic and the major contributing factor in morbidity and mortality. Generally, in individuals with spinal cord injury above T6, systolic blood pressure is 90-110 mmHg.

According to Medscape, an elevation of 20-40mmHg above the reference range for these patients is a sign of autonomic dysreflexia. Quite often this is the only sign or symptom and is associated with increased risk of stroke and chronic disability, according to a Model Systems Knowledge Translation Center spinal cord injury fact sheet.

Patients can develop the syndrome and remain essentially asymptomatic (other than elevated blood pressure, the defining sign of the condition). Lee and Joo in the BioMed Research International article proposed that an elevation above baseline systolic blood pressure of 20 torr acts as a solid definition of autonomic dysreflexia in spinal cord injury patients.

spinal cord injuryUsing ambulatory blood pressure monitoring, they found that 42% of patients present without associated symptoms. Elevated systolic blood pressure was the only indicator of autonomic dysreflexia, according to Medscape.

Symptoms also can present on a continuum and be labile, making diagnosis more difficult. However, sympathetic signs including systolic blood pressure will most often be present. Parasympathetic signs do not appear as much depending on the level of the spinal cord injury, according to an article in BioMed Research International.

Often a reflex bradycardia is present but not to the point that it offsets the elevation in systolic blood pressure. Thus, clinicians should be alert for this combination of signs. Systolic blood pressure is the hallmark of autonomic dysreflexia and the cause of morbidity and mortality. Therefore, even in the absence of all other signs and symptoms, blood pressure must be addressed.

How to treat patients with autonomic dysreflexia

Treatment is straight forward. Remove the offending stimulus. Most often full bladder, constipation, kinked catheter tubing, indigestion, gas, etc., all below the level of the spinal cord injury.

Bladder and bowel problems are the most common precipitators, but any (not necessarily noxious) stimuli can provoke an episode, according to the Model Systems Knowledge Translation Center fact sheet.

Initially treatment may consist of simply sitting the patient up with the legs dependent, followed by removal of any obvious offending stimuli. If first-line remedies prove ineffective, the sustained elevated systolic blood pressure presents a serious medical issue that healthcare provides must address.

In the pre-hospital setting, nitrates can be employed, such as a topical like Nitribid paste. Healthcare providers typically prefer to use Nifedipine as a longer-acting preparation. In the ED setting, nitrate infusions, such as Nipride, can be used. In some cases, one could use an alpha-blocking agent such as Hexamethorium.

Any anti-hypertensive agent, such as clonidine or an anti-cholinergic drug, can be used. Remember that these individuals have become neurologically impaired, and rebound hypotension may ensue.

Alternatively, spinal anesthesia (block) is effective. Spasticity often is associated with spinal cord injury, post the resolution of the paralytic phase of spinal shock. Researchers also think it may contribute to autonomic dysreflexia.

Agents such as botulism toxin have been used primarily for spasticity but they also effects blood pressure by reducing muscle contraction. Gabapentin has been reported to effect autonomic dysreflexia by effecting the glutamatergic neurotransmission, according to the articles “Gabapentin for Spasticity and Autonomic Dysreflexia After Severe Spinal Cord Injury” and “Latest Approaches for the Treatment of Spasticity and Autonomic Dysreflexia in Chronic Spinal Cord Injury.”

Clinicians — especially pre-hospital providers — should be familiar with the presentation of the syndrome. It can be subtle, such as asymptomatic or with vague symptoms.

Common outcomes of autonomic dysreflexia

In rare cases, autonomic dysreflexia can be fatal. But far more likely is significant morbidity leading to further permanent disability, such as stroke.

So physical situation and patient history are crucial in making the diagnosis. Primarily, the patient will have sustained a spinal cord injury within the past year but will be more than one to two weeks post-injury. This is beyond the spinal shock phase of complete paralysis wherein all reflexes below the lesion are suppressed.

Autonomic dysreflexia can occur as soon as 10 days post-injury, but typically occurs sometime later within the first year in about 80% of cases. Important to note here is that a second episode of autonomic dysreflexia is highly likely within a week to 10 days after the first episode, according to an article in Spinal Cord. The injury itself will be at T6 or higher and can be complete or partial.

While making a definitive diagnosis requires a reasonable level of suspicion, one must address the presentation of a hypertensive crisis, i.e. elevated systolic blood pressure greater than 20mmHg over baseline or more than 150 torr, as the mainstay therapeutic approach to this condition.

When encountered in the pre-hospital setting, transport should be considered, even with resolution, as it is either an initial presentation or a recurrent presentation that is not being adequately controlled by current therapies prescribed to the patient.

Either way, further evaluation and often treatment, plus patient and caregiver education, is beneficial.

Take our Critical Care Transport Review to learn more about this topic.