paroxysmal sympathetic hyperactivity
/ PSH, say pee-ess-aitch /
The body has an automatic accelerator, the sympathetic nervous system, that handles the fight-or-flight response: it speeds the heart, raises blood pressure, quickens breathing, brings on sweating, and tenses the muscles, all without conscious thought. Normally the brain keeps a calm hand on this accelerator. After a severe brain injury, the controls can be damaged so that the accelerator jams on by itself, in sudden, dramatic surges that come out of nowhere. These episodes are paroxysmal sympathetic hyperactivity.
Paroxysmal sympathetic hyperactivity, or PSH (also loosely called dysautonomia or sympathetic storming), is a syndrome seen mainly after severe brain injury in which the body has repeated, sudden bursts of overactive sympathetic outflow. An episode looks alarming: a racing heart, a spike in blood pressure, rapid breathing, a high fever, drenching sweat, and often a posturing stiffening of the limbs, lasting minutes to hours and sometimes triggered by something as small as turning the patient, suctioning, or pain. The diagnosis is one of pattern and exclusion, because each individual feature (fever, fast heart) could also mean infection, a blood clot, pain, or seizure, the team must rule those out before attributing the storms to PSH. Crucially, the patient is usually not consciously distressed by the storm itself; it is an automatic over-response, not an emotional one.
PSH matters in rehabilitation in very concrete ways. The repeated surges burn enormous amounts of energy and drive fever and muscle breakdown, worsening weight loss and fueling stiffening that can harden into contractures, so the storms are managed both to calm the body and to protect the limbs (positioning, gentle handling, reducing triggers, and medication to dampen the over-response). Recognizing PSH also prevents harmful mistakes, such as chasing every fever with more and more antibiotics, or treating each blood-pressure spike as a new emergency, when the real problem is the syndrome itself. The honest caveats: PSH is a diagnosis of exclusion that can be missed or over-called; its episodes usually lessen over months as the brain recovers; and the stiffening seen during storms is automatic, not the patient being in agony or fighting care.
Whenever nurses turn a severely injured patient, his heart rate jumps, his blood pressure surges, he sweats through the sheets, his temperature climbs, and his legs stiffen straight, settling after twenty minutes. After infection, clot, and seizure are ruled out, the recurring, trigger-linked pattern is recognized as paroxysmal sympathetic hyperactivity, and care shifts to gentler handling, fewer triggers, and dampening the over-response rather than treating each spike as a new crisis.
A trigger-linked storm of fast heart, high pressure, fever, sweat, and stiffening, once infection and seizure are excluded.
PSH is a diagnosis of exclusion: each feature alone could mean infection, clot, pain, or seizure, which must be ruled out first. The storms are automatic, not the patient consciously suffering or resisting care.