Neurostorming: Symptoms, Causes, and Treatment

After a brain injury, the body’s nervous system can go into overdrive, resulting in a range of intense episodes, or 'neurostorms.' What triggers neurostorming, and what are its symptoms and possible treatment strategies?

What is neurostorming?

Neurostorming, also referred to as paroxysmal sympathetic hyperactivity (PSH), is a severe, episodic condition that typically occurs following significant traumatic brain injuries (TBIs). Neurostorming can occur early after TBI, and, in some severe cases, may even occur in a comatose state, complicating the recovery and management of brain injury due to its unpredictable and dramatic presentation.

Neurostorming occurs in approximately 8–33% of patients with severe TBI. It only occurs in around 6% of patients with any other brain injury, such as stroke or intracerebral hemorrhage.

The role of the nervous system in neurostorming

Neurostorming is due to an overactivity of the autonomic nervous system, which controls the involuntary functions of the body. The autonomic nervous system includes the sympathetic nervous system and the parasympathetic nervous system.

The sympathetic nervous system is responsible for the body’s fight-or-flight response and helps in times of stress, whereas the parasympathetic nervous system counteracts these effects, allowing the body to relax. Neurostorming can occur whenever the sympathetic nervous system becomes overactive or dysregulated.

Symptoms of neurostorming

Since neurostorming involves an overactive sympathetic nervous response, the symptoms can vary from person to person. The common symptoms are:

• High fever (hyperthermia)
• High blood pressure (hypertension)
• Excessive sweating (hyperhidrosis)
• Rapid heart rate (tachycardia)
• High respiratory rate (tachypnea)
• Dystonia (involuntary muscle contraction)

Patients may show significant differences in symptom presentation, intensity, and duration. Most single episodes last from minutes to hours, but recovery time can take from days to months.

Identifying risk factors for neurostorming is crucial due to the challenges in early diagnosis. Some of the risk factors include:

• Age
• Early onset of fever
• Severe injury to the nervous system, such as diffuse axonal injury (DAI)
• Lower scores on the Glasgow Coma Scale
• A surgical opening in the neck to aid in breathing (tracheostomy)

Recognizing these factors may help in quicker identification of neurostorming, potentially reducing the risk of severe complications, like further brain damage.

​​What causes neurostorming?

Neurostorming is a complex phenomenon that occurs after a brain injury. Most cases in patients with TBI are triggered by non-injurious stimuli, such as back patting, turning or rolling over, or even emotional arousal.

Pathophysiology of neurostorming has yet to be fully understood, but multiple theories have been proposed.

Disconnection theory

The Disconnection theory is that after a brain injury, the parts of the brain that normally control the fight-or-flight response can become disconnected from the areas of the brain responsible for keeping this response in check.

Normally, the sympathetic and parasympathetic nervous systems are balanced, but if the control signals are inhibited, this balance can tip, leading to an overactive stress response.

However, the Disconnection theory does not fully explain why neurostorming happens suddenly and intensely (referred to as 'paroxysmal'), so this theory is not widely accepted.

Excitatory/inhibitory ratio (EIR)

The EIR theory suggests neurostorming starts from the impairment in the brain centers, which results in flawed signaling, leading to overactivity in spinal responses. This causes heightened reactions to sensory input.

The theory indicates that spinal overactivity, combined with brain impairment due to brain injury, can result in the unpredictable and severe responses seen in TBI patients. This overactivity is eventually controlled as the brain’s 'calming' system recovers.

Moreover, EIR theory explains that variations in individual responses to stimuli post-TBI are due to changes in how the brain interprets sensory information. The EIR theory is more widely accepted than the Disconnection theory.

Neuroendocrine

The Neuroendocrine theory relates to how, after a TBI, the brain's hormonal control system, specifically the hypothalamic-pituitary-adrenal (HPA) axis, becomes overly active. This leads to excessive release of fight-or-flight hormones like catecholamines (epinephrine and norepinephrine), potentially causing symptoms of neurostorming.

This theory suggests that these hormonal imbalances contribute to the severe symptoms seen in PSH. This is supported by the finding that catecholamine levels can increase 200–300% during a neurostorming episode.

Neutrophil extracellular traps (NETs)

The NETs theory suggests that after a TBI, immune cells called neutrophils release NETs, leading to changes in neurotransmitter levels, such as glutamate and gamma-aminobutyric acid (GABA). This process can overactivate the sympathetic nervous system, potentially contributing to the symptoms of neurostorming.

This theory is supported by animal studies that have shown that the concentration of NETs within a specific part of the brain, the paraventricular nucleus of the hypothalamus, increases after TBI. Additionally, the increase in NETs was associated with an increase in blood catecholamine levels.

Neurostorming treatment

Diagnosing paroxysmal sympathetic hyperactivity (PSH) can be difficult because its symptoms often resemble those of other health conditions. The PSH Assessment Measure (PSH-AM), created in 2014 through international agreement, helps diagnose PSH by evaluating symptoms and their severity. However, it has limitations, such as measuring sweating and tracking changes over time. Despite these challenges, the PSH-AM is useful for detecting PSH early and monitoring its progression.

Due to the complexity and variability of neurostorming, the main goals of treatment are to avoid triggering events, balance excessive nerve activity, and alleviate secondary effects, such as dehydration and fever. The treatment of neurostorming includes both pharmacological and non-pharmacological approaches.

Possible pharmacological treatments include a variety of medications, such as β-adrenergic blockers, opioids, benzodiazepines, neuromodulators, α2-agonists, and muscle relaxants. Propranolol, a β-adrenergic blocker, is often a first-line treatment. Studies have shown that propranolol can help reduce the length of hospital stay and decrease the mortality rate in patients with moderate-to-severe TBI and neurostorming.

Additionally, environmental modification, supportive therapy, and early rehabilitation are emphasized. Likewise, additional hydration may be needed to replace lost fluids to prevent dehydration.

How to avoid neurostorming

Neurostorming episodes can present in a number of ways and even be unprovoked, so it can be difficult to avoid them in patients with a TBI. However, one study highlighted the importance of avoiding the triggers as much as possible. Researchers found that acts as simple as maintaining a stable room temperature and avoiding the use of heavy blankets can decrease the risk of neurostorming.

Life after neurostorming

Recovery from neurostorming and TBI is a long and challenging process, both for the patient and their loved ones. The duration and frequency of neurostorming episodes can vary widely, often lasting from a few hours to several months. Effective management of symptoms is essential in preventing further complications.

Support, patience, and understanding from family members and caregivers play a critical role in the recovery journey​. Family members and caregivers can keep a watchful eye on the patient to look for the first signs of a recurrence so that any potential effects can be minimized.

Neurostorming may be unavoidable for some patients with TBI. Understanding the triggers, symptoms, and risk factors can help decrease the length of the episodes and the adverse effects of neurostorming.