PAROXYSMAL SYMPATHETIC HYPERACTIVITY

"Na tha kuchh to Khuda tha,kuchh na hota to Khuda hota,
duboya mujhko hone ne, na hota main to kya hota"
                                                       - Mirza Ghalib

Paroxysmal sympathetic hyperactivity (PSH) is a syndrome, recognized in a subgroup of severe acquired brain injury patients, of rapid onset, paroxysmal episodes of agitation and dystonia, in association with autonomic symptoms like tachycardia, hyperventilation, fever, diaphoresis and pupillary dilation.

The first case of PSH was reported by Penfield in 1929, as diencephalic autonomic epilepsy. He hypothesized that these episodes are caused by epileptiform discharges in thalamic nuclei, irritated by increased intracranial pressure, a theory which was later refuted.

It has been described in literature by different names like dysautonomia, central autonomic dysfunction, paroxysmal sympathetic storms, midbrain dysregulatory syndrome and paroxysmal autonomic instability with dystonia (PAID).

While PSH can arise from many types of acquired brain injury, but it is most commonly seen in traumatic brain injury followed by hypoxic brain insult and stroke.

It can mimic and difficult to differentiate from SIRS, sepsis, seizures, neurogenic fever, malignant hyperthermia, serotonin syndrome, and sedative/ opioid analgesic withdrawal.

The incidence of PSH in traumatic brain injury patients is estimated to be 8–33 percent.

PSH is associated with worse neurological outcome, longer hospital stay increased financial burden. Prolonged sympathetic activity leads to secondary injury, because of increased metabolic and oxygen demand, cardiac arrhythmias, weight loss, malnutrition and skin breakdown. Increased duration of hospital stay exposes patient to other healthcare associated complications like infection and pressure sores.

●Pathophysiology of PSH is not well understood. Following brain injury, activation of sympathetic nervous system is expected to preserve cerebral perfusion. Parasympathetic nervous system attempts to bring homeostasis by reducing the effect of sympathetic activity.
However, if parasympathetic feedback fails, unopposed sympathetic outflow leads to hyperactivity and PSH.

One hypothesis suggested that autonomic dysfunction results from disconnection between damaged higher order inhibitory centers and intact brain stem/ spinal cord circuits, resulting in uncontrolled sympathetic activity. But pathological and radiological evidences suggested that in patients with PSH, lower brain stem is often damaged, refuting this theory.

More recent excitatory inhibitory ratio (EIR) model proposes that after brain injury even non- noxious sensory stimuli produce sympathetic stimulation and thus PSH. Such stimuli include common nursing interventions, like suctioning, turning, repositioning, bathing as well as physiologic triggers such as constipation, urinary retention and pain.

It has been shown that these stimuli can elicit paroxysms of PSH in brain injury patients, supporting EIR theory.

●Diagnsosis: PSH is a diagnosis of exclusion. Other common conditions mimicking PSH (mentioned above) should be ruled out.

Clinical awareness, recognition of paroxysmal symptoms and their triggers; and early diagnosis and treatment may prevent secondary injury and improve outcome.

Clinical features useful in reaching a diagnosis of PSH are:

•Simultaneity of clinical features,
•Clinical features are paroxysmal in nature,
•Sympathetic overreactivity to non- noxious stimuli,
•Absence of intra-paroxysmal parasympathetic features during episodes,
•Features persist more than 3 consecutive days,
•Features persist more than 2 weeks post-injury,
•Features persist despite treatment of alternative differential diagnoses,
•Medication administered to decrease sympathetic features,
•Lack of alternative explanations,
•Antecedent acquired brain injury.

PSH was defined by the transient presence of four of the following six criteria in the absence of other potential causes such as uncontrolled sepsis or airway obstruction: fever, tachycardia (heart rate>120/ minute or >100 beats/minute if treated with beta-blocker), hypertension (systolic blood pressure>160 mmHg or pulse pressure>80 mmHg), tachypnoea (respiratory rate >30 breaths/minute), excessive diaphoresis and extensor posturing or severe dystonia.

●Management:
•Limiting afferent sensory processing to limit allodynia,
•Inhibiting central sympathetic outflow,
•Blocking end organ response.

Gabapentin and baclofen inhibit afferent sensory processing in spinal cord.

GABA A antagonist (Diazepam, lorazepam, propofol), dopamine agonists (bromocriptine) and opioid agonists (morphine) inhibit central sympathetic outflow.

Alpha adrenergic agonist (clonidine and dexemedetomedine) and beta blockers (propranolol) reduce both central and peripheral sympathetic activity.

Of all these morphine, benzodiazepines, propranolol and bromocriptine is found to be most effective.
Gabapentin reduced number of paroxysms and reduces other medication requirement. It helps in acute as well as chronic phase of PSH.
Bromocriptine is particularly helpful in reducing fever and dystonia. But it decreases seizure threshold and contraindicated in uncontrolled hypertension.
Clonidine and propranolol is much effective in controlling tachycardia, hypertension, diaphoresis and fever.

References:
Paroxysmal sympathetic hyperactivity in the neurological intensive care unit. Rabinstein AA. Neurological Research 2007.
Paroxysmal sympathetic hyperactivity after severe brain injury. Devon Lump. Curr Neuroll Neurosci Rep 2014.
Paroxysmal           sympathetic           hyperactivity         afteracquired        brain       injury:     A             review of diagnostic criteria. Brain Injury, September 2011.