By: Heidi Reyst, Ph.D., CBIST
Rainbow Rehabilitation Centers
Storming, What’s in a name?
Commonly referred to as “storming,” Paroxysmal Sympathetic Hyperactivity (PSH) is a nervous system disorder that affects 15 to 33 percent of people who have sustained a severe traumatic brain injury (TBI). Onset of symptoms can occur within hours or months of the injury, and for family members with little medical background, the signs can be alarming: rapid breathing, sweating, agitation and abnormal posturing are just a few (Lemke, 2007).
What is PSH, what causes it and how can it be treated? Before we begin, let’s briefly address the name, Paroxysmal Sympathetic Hyperactivity. Over the years, it has been known by a variety of names, many which have evolved through attempts to describe its symptomology or the etiology. For example, Baguley (1999) noted that individual cases of the disorder have had varied names such as “paroxysmal sympathetic storms”, “autonomic dysfunction syndrome”, “fever of central origin” and “acute midbrain disorder.” The term PSH is used here because it best describes the current knowledge. A quick overview of the name itself will illustrate a few basic concepts of PSH.
First, a paroxysm is a sudden recurrence or attack of a disease or a sudden worsening of conditions. Second, sympathetic refers to the “fight or flight” portion of our autonomic nervous system. Lastly, hyperactivity describes the state of the sympathetic system when “storming” occurs.
Definition and Diagnosis
Now that we understand its varied naming conventions, it should be easier to determine what PSH is, however that too is not so easy. In fact, PSH is a conglomeration of symptoms, with a diagnosis by exception. Let’s begin with symptoms:
Hypertension—increased blood pressure
Tachycardia—abnormally rapid heart rate
Tachypnea—abnormally rapid breathing Dystonia—state of abnormal muscle tone
Hyperthermia—abnormally high body temperature, of central origin
Posturing—abnormal muscle stiffness/body positioning
Diaphoresis—abnormal/excessive degree of sweating
Different medical professionals have applied differential symptomology requirements for a definitive PSH diagnosis. For example, one definition requires at least one paroxysm (sudden onset of symptoms) that includes tachycardia, hypertension, hyperthermia, tachypnea, dystonia, posturing or diaphoresis, to occur at a rate of at least one cycle per day (noted in Liu, Jolly, Pokala, 2010). Another definition (Baguley, Nicholls, Felmingham, Crooks, Gurka and Wade; 1999) defined it as “simultaneous, paroxysmal increases in at least five out of seven reported features”…“with episodes persisting for at least two weeks after injury.” Perkes, Baguley, Nott, and Menon (2010) noted that since 1993, there have been nine published sets of diagnostic criteria for PSH, with no single agreed upon definition within the field.
Because there is no single test to rule in PSH, like one would have in many other diseases or conditions (e.g., a blood test for thyroid disorder), clinicians must rule out any metabolic or infectious causes to symptoms. Once other symptom causes can be ruled out, a definition like those above can be used to positively diagnose PSH. While no fully agreed upon diagnosis
is consistently used, the key feature in diagnosing PSH is that there must be clear clinical presentation of symptoms, along with a consistency to their sudden onset over time.
A retrospective study by Baguley, Nicholls, Felmingham, Crooks and Wade (1999) found significant statistical differences across clinical symptoms between individuals diagnosed with PSH versus control groups who had PSH ruled out. For seven of the eight clinical features, the data show that patients with PSH had significantly higher frequencies of sweating, tone, posturing, hypertension, diffuse axonal injury, brainstem injury and pre-admission hypoxia than did the control patients (see Table 1). This lends support to the diagnostic criteria outlined above for PSH. While the first clinical features represent symptomology (sweating, tone, etc), the last two in Table 1 represent potential etiologies of PSH. In other words, it begs the question of “who gets PSH?”
The Causes of PSH
PSH is rarely reported without an identified etiology (cause), and it has been associated primarily with TBI. Perkes, Baguley, Nott, and Menon (2010) found that of 349 cases identified in the medical literature, 277 (79 percent) were preceded by the onset of TBI. The remaining 21 percent were sub-categories of acquired brain injury (ABI), as shown in Table 2. Kishner, Augustin, and Strum (2013) noted that diffuse axonal injury and brainstem injury have been identified as causes of PSH at higher rates. Rabinstein (2007) found that 33% of patients with TBI met the diagnostic requirements of PSH, relative to only 6 percent of patients with other acute neurological diagnoses.
Some authors have noted that PSH is notably more likely to occur in patients with severe TBI with Glascow Coma Scores of 3 to 8 (Lemke; 2004) or Ranchos levels I to IV (Kishner; 2013). This paints a clearer picture of patient morbidity – these are individuals who are typically at a low level neurologically, and may be in a vegetative or minimally conscious state. Collectively, however, the information thus far does not clearly identify the etiological factors of exactly what causes PSH, but only identifies that neurological trauma is a precursor. To identify proper treatment for PSH, physicians and clinicians need to understand the pathophysiology causing the myriad of symptoms individuals with PSH experience.
Many different root causes have been hypothesized, including brain sites of dysfunction ranging from the brain stem, to the diencephalon to the orbital frontal cortex. Other root causes have been hypothesized including epilepsy and seizures, though EEG testing has ruled out seizure as a source (Do, Sheen and Bromfield, 2000). What then is the prevailing wisdom regarding PSH pathophysiology? To answer this question, we need to turn to the title again, focusing on the Sympathetic Hyperactivity aspect because it tells us that “storming” is likely the result of an overactive sympathetic nervous system.
To speak to the sympathetic nervous system, we need to address first the autonomic nervous system in which the sympathetic system resides. The autonomic nervous system (ANS) is a control system that operates largely outside of our conscious control. It controls (through innervation) such areas as cardiac and smooth muscle, endocrine and exocrine (hormonal) functions and as McCorry (2007) points out, it “influences the activity of most tissues and organ systems in the body.” There are a variety of brain areas which contribute to ANS functions including the brainstem, the diencephalon (particularly the hypothalamus), and even areas of the cerebral cortex and the limbic system (the amygdala in particular).
Vital functions are controlled by the ANS, including heart rate, blood pressure, gastrointestinal peristalsis, temperature, hunger, thirst, plasma volume, and plasma osmolarity (McCorry, 2007).
There are two anatomically and functionally distinct subsystems of the ANS that operate in a parallel, yet complimentary fashion and play a vital role in the maintenance of homeostasis. One is the parasympathetic system which is responsible for vegetative functions occurring when the body is at rest (e.g., stimulation of salivation and digestion, contraction of bladder, inhibition of the heart, and is commonly called the “rest and digest” functions. The other is the sympathetic system which controls activities essential to preparing us for physical activity, allowing the body to function under stress (e.g., pupil dilation, accelerated heart, inhibited digestion), and is commonly termed the “fight or flight” response. With regard to PSH, while the precise mechanism is still unknown, it is been theorized to be a direct result of a loss of balance between the parasympathetic and sympathetic nervous systems of our ANS.
A key aspect of both systems is that they provide in McCorry’s (2007) words, “some degree of nervous input to a tissue at all times.” This means that at any moment, the parasympathetic system or sympathetic system can influence tissue by either inhibiting or enhancing through neuronal firing. Typically the two subsystems have diametrically opposed effects on the tissue whereby one system would inhibit (e.g. the sympathetic system inhibits bladder contraction), and the other would enhance (e.g., the parasympathetic system contracts the bladder). See Figures 1 and 2.
With regard to PSH, it is thought that an imbalance between the parasympathetic and sympathetic system causes the parasympathetic system to be ineffective in counterbalancing the sympathetic system. This renders the individual in an uncontrolled sympathetic response (ready for physical activity), where pupils dilate, salivation is inhibited and the heart accelerates, to name a few. Baguley, Nicholls, Felmingham, Crooks, Gurka and Wade (1999) hypothesized a three stage process post injury to explain storming:
Patients are receiving paralytics or are sedated to prevent edema, and there is no identifiable difference between those who will incur PSH and those who do not.
The onset of PSH occurs and termination is signaled by the cessation of diaphoresis. The average termination is 74 days post injury.
The paroxysms have stopped, but the patient likely has residual dystonia and spasticity, with amounts varying from patient to patient. There is little known about what causes the sympathetic system to become hyperactive, but a number of theories have been proposed. Perkes, Baguley, Nott, and Menon (2010) noted three in particular. The first related to assumptions that the brainstem excitatory centers no longer have cortical control over them, resulting in a hypersympathetic state. The second relates to a model termed the Excitatory/Inhibitory Ratio model, where the hyperactivity originates at the spinal cord level. The third theory relates to an association between afferent stimuli (information from the body to the brain) and the sympathetic hyperactivity. Some evidence, has shown that the afferent stimuli theory has the most traction. Baguley, Hersineau, Gurka, Nordenbo and Cameron (2007) and Lemke (2007) both noted that “noxious” yet “trivial” stimuli such as suctioning, equipment alarms, repositioning, etc., can bring about paroxysms. Perkes, Baguley, Nott, and Menon (2010) urged further study of the pathophysiology of PSH, and noted that “over-reactivity to afferent stimuli may be the hallmark of PSH.”
Importance of Treatment
Regardless of whether the mechanisms are known or unknown today, there is ample reason to focus on treatment of PSH. The main reason is that without treatment, there is potential for increased morbidity as a result of PSH. Hyperthermia that could result in secondary brain injury is one such concern. In Baguley, Nicholls, Felmingham, Crooks, Gurka and Wade (1999), 73% of the patients with PSH, had core temperatures above 38º C (100.4º F) for up to two weeks post injury, with 24% continuing for four weeks post injury. Another concern is decerebrate or decorticate posturing. This greatly increases the patients’ energy expenditures (ranging from 100 to 250 percent), which results in weight loss and permanent cardiac and skeletal muscle damage.
Lemke (2007) noted a variety of secondary concerns that can lead to increased morbidity. There can be increased secondary brain injury due to decreases in cerebral tissue oxygenation. Hypertension can also impact secondary injury due to risk of bleeds as well as cardiac arrhythmias resulting from storming that can lead to long-term cardiac dysfunction. Increased metabolic activity can lead to increased blood sugar levels and core temperatures, potentially resulting in muscle waste and weight loss, and kidney dysfunction among others. Lemke also noted that “the ultimate goal is rapid control of the signs and symptoms of excess activity of the sympathetic nervous system to prevent secondary complications of prolonged stress and to facilitate rehabilitation.” What then are treatment options for PSH?
The treatment and management of PSH to date has been pharmacologically based, with the most common drugs being those that depress the central nervous system, and therefore suppress the sympathetic nervous system (Lemke, 2007). Common medications include morphine, fentanyl, and midazolam. Intrathecal Baclofen has been successful while limiting the sedating effects of some other medications (reported in Lemke, 2007). To a large degree treatment protocols vary by practitioner, and can be described as “trial and error” based on patient response to the medication protocols. In addition, other medications are used to target specific symptoms, and Lemke (2007) has an excellent overview of medication use and their actions to treat PSH. Treatment and a better understanding of the pathophysiology are two areas that are in need of further research. Better understanding of the mechanisms of PSH will help to guide better treatment, if not prevention. More precise treatment protocols will also assist with ensuring that long term comorbidities are prevented.
As the adage goes, a brain injury often happens to the whole family, and not just the individual with the injury, because of the often enduring and lifelong changes that occur to both the individual and their family and social network. To that end, education of the family regarding PSH is extremely important. First and foremost, they may be the first to see the signs and symptoms as they occur, and can be a crucial part of keeping their loved one comfortable. As Lemke (2007) notes, it can also be beneficial to the family, in that active involvement can reduce feelings of helplessness in dealing with their loved ones injury.
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