Paroxysmal Sympathetic Hyperactivity: Ignoring the Presence of an Elephant in the Room

infection, malnutrition, dehydration, tracheostomy, longer hospitalization longer intensive care unit (ICU) stays, contractures, and heterotopic ossification. PSH remains an under-recognized condition that is difficult to diagnose. A high index of suspicion is key to early diagnosis. The first step in diagnosis is to exclude conditions with similar symptoms, such as infection, sedation withdrawal, seizures, and pulmonary embolism. Clinical diagnostic tools (PSH assessment measure) have been proposed to assist clinicians in the reliable identification of PSH.8 Such tools incorporate a clinical feature scale that categorizes the severity of sympathetic signs during episodes and a diagnostic tool that gauges the likelihood of diagnosis of PSH based on the presence of characteristic features. These two components are combined in a score that reflects the degree of confidence in diagnosis of PSH. The feasibility and reliability of these tools have been recently validated by van Eijck et al.9 There is evidence that they may reduce the chances of misdiagnosis and favorably impact hospital length of stay and costs of hospitalization.10 The pathophysiology of PSH is poorly understood and the dominant theory suggests the failure of the central autonomic network. Disruption of descending pathways releases sympathetic responses from their normal inhibitory modulation. The consequence is that sympathetic responses to internal or external stimuli become exaggerated.11 The interruption of descending inhibitory modulation might also produce maladaptive changes in the spinal cord leading to excitatory interneuronal activity.12 These changes could help explain how non-noxious stimuli are perceived as noxious by brain.12 While formal evidence on treatment is scant and lacks methodological quality, PSH is a disorder that can be treated.13 Can episodes be prevented with pharmacological intervention? There is at least one retrospective study that claims so. Tang et al asserted that dexmedetomidine infusion has Paroxysmal sympathetic hyperactivity (PSH) is a syndrome of excessive and pathological adrenergic output to nociceptive or non-nociceptive (including environmental) stimuli. It is observed as a complication of various acute brain insults such as traumatic brain injury (TBI), stroke, anoxic brain injury, tumors, infections, autoimmune encephalitis, and acute hydrocephalus. It can manifest as a constellation of episodic, simultaneous symptoms such as tachycardia, hyperthermia, hypertension, tachypnea, and diaphoresis, often accompanied by dystonia and even motor posturing.1 Onset of these symptoms is usually fast, but resolution is slow, unless terminated by medication. Since the first description of this syndrome by Penfield,2 many names have been ascribed to it which has created puzzlement in its diagnosis as well as understanding of its pathophysiology. Some of the names associated with this condition over the years are “autonomic storm,” “sympathetic storm,” “hypothalamic dysregulation syndrome,” and “paroxysmal autonomic instability with dystonia.” In 2014, the International Brain Injury Association proposed the term “paroxysmal sympathetic hyperactivity.”3 Its overall incidence is 18% among various cohorts of patients admitted in neurocritical care with an incidence of 33% in severe TBI patients.4 According to Perkes et al, 80% of cases of PSH are observed after TBI, and the remaining 20% following other cerebral pathologies.5 The most consistent observation is that patients with PSH are frequently young and comatose. Pediatric patients appear more prone to develop PSH after anoxic–ischemic insults and with non-bacterial encephalitis.6 It is common that patients with PSH are erroneously suspected of having other diagnoses, and this may lead to unnecessary testing and sometimes inappropriate treatments, making an early and accurate diagnosis important.7 PSH may persist for weeks or months, and has been associated with worse clinical outcomes such as increased time of mechanical ventilation,