Your patient is a 2-year-old female who is in the Pediatric Intensive Care Unit after suffering an out-of-hospital cardiac arrest. She is currently intubated and sedated. The team is providing post-cardiac arrest standard of care. Advanced neuroimaging 48-72 hours after her arrest revealed that the patient suffered a significant hypoxic ischemic brain injury. About one week into the treatment course, after having no significant changes in mental status, the patient begins to exhibit tachycardia, random eye movements, dilated pupils bilaterally, and hyperventilation. These symptoms lead you to be concerned that the patient is experiencing an intracranial hemorrhage leading to a possible herniation. You order mannitol to be administered STAT and rush the patient to the CT scanner.
General Overview
Paroxysmal Sympathetic Hyperactivity (PSH) describes the dysregulation of the sympathetic nervous system. This disease process typically occurs in the setting of severe acquired brain injury, which can include traumatic brain injury, anoxic brain injury, stroke, tumors, etc. In general, patients with severe PSH symptoms are more likely to suffer from poorer neurological outcomes. PSH is characterized by sudden, recurrent episodes of excessive sympathetic nervous system activity. These episodes are typically brief, intense, and often triggered. Previously, PSH has been referred to by various terms, including "sympathetic storming," "autonomic storming," and "paroxysmal autonomic instability with dystonia."
Pathophysiology
Autonomic dysfunction is a result of disconnection of one or more cerebral centers and/or disturbances in cortical and subcortical regions caused by focal or diffuse injuries. PSH arises when inhibitory pathways are disrupted, resulting in dysregulation of the sympathetic nervous system. Ultimately, the anatomic basis of the pathogenesis of PSH remains undefined.
Clinical Presentation
PSH manifests as simultaneous, paroxysmal transient increases in sympathetic and motor activity. The six core features include tachycardia, tachypnea, hypertension, hyperthermia, hyperhidrosis, and dystonic posturing. PSH can present as a spectrum of these clinical symptoms over time. Even within the clinical course of one patient, the presentation may fluctuate.
Triggering events are not predictable and may include both noxious and non-noxious stimuli including pain, suctioning, passive motion, bladder/bowel distension, etc. It is unknown when PSH will first present within the clinical course of a patient recovering from brain injury. Some patients experience PSH one week into the clinical course and others will experience PSH weeks to months into recovery. It is also difficult to predict the duration of each episode and for how long a patient will continue to experience these paroxysmal events. Episodes may last from a few minutes to 2 hours and occur frequently throughout the day; some patients may experience PSH for several weeks to months to years.
Signs and symptoms associated with PSH:
- Tachycardia (present in ~98% of cases)
- Hypertension
- Tachypnea
- Diaphoresis
- Pupillary dilation
- Hyperthermia
- Dystonic posturing
- Agitation
Differential Diagnosis
Because the presentation of PSH is broad, unpredictable, and nonspecific, other disease states should be considered.
|
Diagnoses to consider |
Overlapping signs/symptoms |
Management next steps: |
|
Seizure |
Posturing, hypertension, tachycardia, gaze deviations and pupillary exam changes |
EEG monitoring and administration of antiepileptics |
|
Pulmonary Embolism |
Tachycardia, tachypnea |
CTPE, vasopressor support and/or thrombolytics, troponin, echo |
|
Elevated intracranial pressure |
Pupillary dilation, hypertension, irregular breathing pattern |
CT Head, hypertonic saline/mannitol, hyperventilation, elevation of head of bed |
|
Pain or agitation episodes |
Tachycardia, hypertension, rigors, tachypnea |
Analgesia |
|
Drug withdrawal and intoxication syndromes (i.e. alcohol, cocaine, meth, opioids) |
Hypertension, tachycardia, tachypnea, hyperthermia |
Symptomatic management |
|
Serotonin syndrome or neuroleptic malignant syndrome |
Hyperthermia, tachycardia, hypertension, posturing/rigidity, changes in reflex testing, pupillary dilation |
Review of medication list and symptom control |
|
Thyrotoxicosis |
Tachycardia, hypertension, tachypnea, changes in reflex testing |
Ancillary hormone testing (TSH, T4 free, T3) |
|
Sepsis |
Tachycardia, hyper/hypotension, tachypnea, agitation, hyper/hypothermia |
Serum testing (CBC with diff, CMP, lactic acid, blood cultures), antibiotics |
|
Pheochromocytoma |
Hypertension, tachycardia, diaphoresis |
Alpha and beta blockade, CT imaging to identify source |
Ultimately, PSH is a clinical diagnosis of exclusion.
Treatment/Management
Treatment is largely supportive and relies on counteracting the sympathetic overdrive with a combination of abortive and preventive medications. The goal is to reduce the frequency and severity of episodes. Ideally, pharmacologic treatment will be initiated in the ICU and tailored to individual needs.
Abortive Therapy (Managing Acute Episodes)
- Opioids: Morphine (2–8 mg IV); responsiveness supports the PSH diagnosis. Fentanyl (25-100 mcg IV) offers a faster onset.
- Propofol: GABA agonist; good option in intubated patients; a 10–20 mg IV bolus can abort episodes.
- Benzodiazepines: GABA agonist; diazepam (5–10 mg IV) or midazolam (2–5 mg IV).
Preventative Therapy (Reducing Episode Frequency)
- Propranolol: A lipophilic non-selective beta-blocker that crosses the blood-brain barrier; doses range between 20-60 mg PO every 4-6 hours.
- Gabapentin: Addresses neuropathic pain and allodynia; starting dose is 100-300 mg PO three times daily.
- Alpha-2 agonists: Clonidine (0.1 mg PO every 8 hours) or dexmedetomidine infusions can modulate central sympathetic activity.
Supportive Care
- Trigger Avoidance: Minimize stimuli such as environmental temperature changes, bladder distension, etc.
- Nutritional Support: Address increased metabolic demands due to heightened sympathetic activity.
- Fluid Management: Counteract volume depletion from insensible losses due to hyperventilation or diaphoresis
- Temperature Control: Use physical cooling methods, as fevers may not respond to antipyretics.
- Medication Caution: Avoid antipsychotics, which may increase the risk of neuroleptic malignant syndrome in PSH patients.
Disposition
ICU Monitoring: Patients with PSH require close observation, especially during the acute phase.
Long-Term Outlook: PSH episodes typically resolve within a year; however, some patients may experience prolonged symptoms.
Rehabilitation: Early involvement of multidisciplinary teams can aid in recovery and functional improvement.
Prognostication: PSH is associated with worse long-term functional outcomes. There is limited data to determine the directionality of this relationship though it is worthwhile to note that patients with PSH often have increased duration of hospital stay, higher rates of tracheostomy, and/or longer ventilator dependence.
Summary/Take-Home Points
- Paroxysmal sympathetic hyperactivity (PSH) is a serious but treatable complication of acute brain injuries.
- The clinical presentation includes recurrent episodes of tachycardia, hypertension, tachypnea, hyperthermia, diaphoresis, and dystonic posturing. Episodes are unpredictable and rapid in onset.
- The diagnosis is based on clinical features.
- It is important to consider a broad differential diagnosis, given PSH shares many overlapping symptoms with other severe pathologies.
- Management includes supportive care and pharmacologic therapy.
- PSH is associated with a worse prognosis for recovery in patients with severe traumatic brain injury as well as a higher likelihood of complications.
Case Resolution
Imaging reveals no new lesions or intracranial abnormalities. The patient returns to their room. Over the course of the same day and the next week, these episodes of sympathetic response occur more frequently and become regular events. It is deduced from the clinical picture and continuous monitoring that the patient is “neuro-storming,” also known as paroxysmal sympathetic hyperactivity. The patient is started on a dexmedetomidine infusion and has morphine added as a PRN medication for when the episodes occur.
References
Leggett BD. Treating Paroxysmal Sympathetic Hyperactivity in Children: The Known Unknowns. Hosp Pediatr. December 2023; 13 (12): e390–e391.
“Paroxysmal Sympathetic Hyperactivity (PSH).” EMCrit Project, https://emcrit.org/ibcc/psh/. Accessed 22 May 2025.
Rabinstein AA. Paroxysmal Sympathetic Hyperactivity. UpToDate. Accessed 22 May 2025.
Zheng RZ, Lei ZQ, Yang RZ, Huang GH, Zhang GM. Identification and Management of Paroxysmal Sympathetic Hyperactivity After Traumatic Brain Injury. Front Neurol. 2020 Feb 25;11:81.