Autonomic Hyperreflexia

Definition

Autonomic hyperreflexia, also known as autonomic dysreflexia, is a clinical syndrome associated with cervical and thoracic spinal cord injuries (SCIs). Autonomic hyperreflexia episodes are usually characterized by an acute, and often dramatic, increase in blood pressure in association with a stimulus below the level of the spinal cord lesion. This elevation in blood pressure can be accompanied by bradycardia or (more rarely) tachycardia. The clinical criteria for an autonomic hyperreflexia episode includes an increase from baseline systolic blood pressure of at least 20% associated with at least one of the following symptoms: sweating, chills, goose bumps, flushing, or headache. Intensity of an autonomic hyperreflexia episode can vary from asymptomatic to a life-threating hypertensive emergency. During an episode of autonomic hyperreflexia, an offending stimulus below the level of the spinal cord lesion leads to sympathetic nervous system activation that is no longer opposed by inhibitory descending parasympathetic pathways, as occurs in patients without SCI. This sympathetic activation below the SCI lesion leads to extensive vasoconstriction of the peripheral circulation and of the splanchnic vasculature that accounts for the majority of the vascular capacitance in humans. It also causes mild to malignant elevations in blood pressure.

An autonomic hyperreflexia episode can be triggered by activation of pain fibers below the level of the spinal cord lesion whether the patient has sensation or not. Such stimuli can include distention or contraction of hollow organs such as bowel or bladder, with bladder distention being the most common cause of autonomic hyperreflexia episodes overall. Gastroesophageal reflux, gastritis, gallstones, fecal impaction, hemorrhoids, obstruction or manipulation of indwelling urinary catheters, urologic procedures, pregnancy, childbirth, and surgical procedures have all been implicated in triggering autonomic hyperreflexia. Other triggering events can include spasms, temperature alterations, sexual intercourse, bone fractures, or hip dislocation.