AD classically presents as sudden, severe, uncontrolled hypertension and accompanying bradycardia . The amount of the rise in blood pressure that is required to diagnose AD remains a matter of dispute [8]. It has been proposed that a minimum increase of systolic blood pressure of 20mmHg from baseline is diagnostic for AD [3, 4]. Another proposal suggests a rise in blood pressure by 20% with at least one accompanying symptom [8, 22]. Of note, clinicians should be aware that the basal systolic and diastolic blood pressure in SCI individuals is approximately 15 mmHg lower than in neurologically intact persons, as a result of reduced sympathetic activity [30]. Although reflex bradycardia typically forms the episode of AD, it is seen in only 10% of cases [16, 18, 31]. The majority of patients with AD present with tachycardia, arrhythmias (atrial fibrillation, premature ventricular contraction, atrioventricular conduction abnormalities), or even with no significant change in heart rate.

In daily clinical practice, patients also present with various and non-specific symptoms and signs. To make matters worse, patients may experience one or more of them in diverse combinations and with varied intensity from uncomfortable symptoms to life-threatening crises. The other clinical features of AD are [5, 8, 9]:

Some SCI patients may be entirely asymptomatic (silent AD). It has been estimated that 35–50% of those after injury at T6 or above may have significantly elevated blood pressure without any other symptoms or signs of AD [10, 17, 31, 32]. In these cases, the diagnosis of AD may be established by inducing the condition in a controlled setting, such as by the bladder filling during urodynamic study with appropriate blood pressure and pulse monitoring [10, 20, 32]. One-minute intervals of monitoring have been proposed [20]. Furthermore, this approach might be particularly useful for educating the patient regarding the recognition of early warning symptoms and signs that will enable immediate preventive measures to be taken [9, 33]. This also emphasizes the need for appropriate blood pressure and pulse monitoring of these patients during any instrumentation (e.g., cystoscopy) at regular intervals, as a significant number of them may be asymptomatic [8]. Episodic recurrence of AD may in itself be an important clinical sign of underlying disease or developed complications of neurogenic bladder (e.g., urinary tract infection, uriolithiasis) and should raise special attention. The differential diagnosis of recurrent AD should also include pheochromocytoma, migraine and cluster headaches, posterior fossa neoplasms, toxemia of pregnancy, and uncontrolled hypertension [9, 14].

AD may have dramatic and extremely serious consequences if not appropriately treated in timely manner or left uncontrolled. Reported consequences include subarachnoid hemorrhage (as systolic blood pressure may rise up to 300 mmHg and diastolic up to 220 mmHg) [11, 12, 18, 34], intracerebral bleeds [35], hypertensive encephalopathy [36], retinal hemorrhage [9], cardiac arrhythmias/myocardial failure [37, 38], seizures/convulsions [39], neurogenic pulmonary edema [40], renal failure (prolonged vasoconstriction in the renal vascular bed) [41], coma [42], and death [34]. Death occurs most commonly when associated with complications of the central nervous system [43]. Nevertheless, proper management significantly decreases the likelihood of these complications.

Early recognition of AD is important. Immediate management aims to identify and treat the triggering factor/factors as well as manage the hypertension and/or other potential complications. The patient should be seated with head raised and the blood pressure should be continuously measured (every 2–5 min), as significant and rapid fluctuations in these parameters may appear [34, 44]. The triggering factor /factors should be immediately identified and adequately stopped/removed. Removal of the precipitating stimulus may reverse the onset of acute episode of AD without the need for additional treatment (including pharmacological agents). Any constrictive devices and tight clothing, including belts, dressings, plaster casts, and catheter leg bags, should be loosened. As the commonest cause of AD is bladder overdistension , bladder catheterization should be employed. If the patient has already been catheterized, free drainage of urine down the catheter tubing into the drainage bag is of utmost importance. Therefore, any catheter, tubing, and bag should be checked for obstruction and, if required, irrigated (with 10–15 mL of warm saline) or replaced (if previous attempt to relieve the obstructed catheter has failed to decompress the bladder). Both large volumes and cold irrigation solutions should be avoided because they can also exacerbate AD. If there is no catheter, the patient should be catheterized as soon as possible. As catheterization itself can exacerbate AD, intraurethral lidocaine jelly 2% should be generously applied at least 2 min before insertion or change of a urethral catheter in order to decrease sensory input and relax the urinary sphincter [44]. A coudé tip catheter may be considered if catheterization is difficult or associated with bladder neck obstruction. Neither the Valsalva nor the Crede maneuver should be attempted to empty the patient’s bladder because these could increase the severity of the syndrome [45]. When the clinical scenario indicates urinary tract infection as a potential cause of AD, a urine sample should be examined by dipstick analysis and sent for microscopy and culture for infection. Moreover, high-dose intravenous antibiotics should be considered. Rectal examination for fecal impaction with gentle manual evacuation should be considered if there is no urological cause found for the presenting condition and blood pressure remains elevated after bladder catheterization [44]. As additional stimulation may further exacerbate AD, it is recommended to perform gentle disimpaction after introducing intrarectal lidocaine jelly 2% for at least 2 min before the maneuver. However, a prospective randomized study has failed to show any significant difference between the use of 2% topical lidocaine jelly and controls prior to anorectal procedures [46]. If AD worsens during rectal manipulation, the manual evacuation should be stopped and rechecked after 20 min. Skin examination should be performed to identify superficial infection and bed sores. The external genitalia should be examined to look for epididymitis/orchitis or testicular torsion, and the perianal areas should be checked for other conditions such as thrombosed hemorrhoids, thrombophlebitis, and perianal abscesses [9]. If the triggering factor has not been identified, acute abdominal conditions (e.g., appendicitis, intestinal obstruction, peritonitis, pyelonephritis) must be urgently excluded [5]. It is noteworthy that this more in-depth investigation of the triggering cause should not preclude the course of emergency treatment. Thus, if the blood pressure remains high (≥150 mmHg) despite bladder catheterization or rectal evacuation, or the triggering factor remains unclear or not found within the first few minutes, antihypertensive drugs should be introduced [1, 44, 47]. These include:

Of note, when nitrates are considered , it should be made certain that the patient has not taken phosphodiesterase 5 inhibitors (e.g., sildenafil, tadalafil, vardenafil) in the past 24–48 h (risk of precipitous hypotension) [47]. This check is especially important, as a large proportion of male patients after SCI have coexisting erectile dysfunction, for which they are likely to take these drugs. When nifedipine is considered, clinicians should keep in mind the possible serious adverse events, including cerebrovascular accident, myocardial infarction, or even death, reported in hypertensive emergencies of non-SCI individuals [53]. Caution with nifedipine use might therefore be necessary and cardiovascular monitoring may be helpful even though a review of the literature has not shown any reported adverse effects of nifedipine when used to treat AD [44]. Furthermore, oral nifedipine has been shown clearly effective in treating severe hypertension in the acute setting and has a role in preventing the significant morbidity and potential mortality associated with AD [9].

Patients should be monitored for at least 2 h (up to 48 h) following resolution of AD, depending on the acuity of the episode (patient should be monitored for both recurrent AD and hypotension) [47]. They should be educated in how to monitor their symptoms to identify a possible recurrence. Patients might also experience hypotension after resolution of the trigger, especially if the patient has been given antihypertensive medication . If hypotension occurs, the patient should be placed supine with legs elevated. Administration of intravenous fluids and adrenergic agonist may be considered if the hypotension is symptomatic or refractory [42].

All episodes of AD should be carefully documented in medical records and should include information regarding signs and symptoms at presentation, the trigger responsible for the acute episode, the treatment instituted, and treatment outcomes. If blood pressure and heart rate came back to normal, the noxious stimulus has been removed and symptoms resolved, the patient can be routinely followed up. In cases of persistent AD or when the noxious stimulus has not been identified, the patient should be admitted or sent to the emergency department [47]. Spinal anesthesia has been recommended in an acute episode of AD refractory to medical management, as it successfully blocks the sympathetic response [54].