Recognising and differentiating paroxysmal sympathetic hyperactivity after severe traumatic brain injury: a practical diagnostic approach.

Paroxysmal sympathetic hyperactivity (PSH) is a syndrome seen in a subgroup of survivors of severe acquired brain injury, most often traumatic, in which episodic surges of sympathetic activity occur together with motor over-activity, typically dystonic posturing. It is associated with longer intensive care stays, more complications, and worse outcomes, yet remains under-recognised. The difficulty is twofold: its core features overlap with the common emergencies of the intensive care unit, so that sepsis, seizures, pulmonary embolism, and drug-related syndromes are reasonably considered first; and no biomarker or imaging finding confirms it. This review offers a practical two-part approach for the patient with severe traumatic brain injury: how to recognise the syndrome positively, using the consensus definition and the PSH Assessment Measure, and how to differentiate it from its mimics. The differential is extended beyond the conditions usually listed to include autonomic dysreflexia, iatrogenic and substance withdrawal, endocrine emergencies, non-convulsive status epilepticus, unrelieved pain, and drug-induced autonomic instability, and the limitations of the evidence are examined rather than assumed. Attention is given to the pitfalls that cause delay and to the frequent coexistence of PSH with conditions such as sepsis. The evidence is drawn into a stepwise framework which has not been prospectively validated and is offered as an educational aid rather than a clinical guideline. Throughout, the emphasis falls on serial reassessment and dynamic reasoning, since substantial diagnostic uncertainty commonly persists.