Paradoxical reflex bradycardia in paroxysmal sympathetic hyperactivity following traumatic brain injury: a case report.

Background: Paroxysmal sympathetic hyperactivity (PSH) is a devastating complication of traumatic brain injury (TBI), characterized by the simultaneous onset of various manifestations due to sympathetic overactivity. Paradoxical bradycardia, an uncommon manifestation of PSH, is poorly characterized, and there is limited evidence regarding its clinical features, pathophysiological mechanisms and targeted management. Case presentation: A 25-years-old male sustained severe traumatic brain injury in a nighttime motorcycle collision with a parked vehicle and underwent multiple neurosurgical procedures. He developed typical PSH on day 48 post injury, with a Paroxysmal Sympathetic Hyperactivity Assessment Measure (PSH-AM) score of 27. On the 92nd day post-injury, the patient developed persistent resting bradycardia (40-66 beats/min) after cranioplasty, while a reduced maximum heart rate (140-159 beats/min) was noted during PSH episodes. He subsequently experienced an acute PSH episode with severe bradycardia (38-43 beats/min, PSH-AM score of 20). After excluding common predisposing factors, intravenous isoproterenol (initial dose 4 μg/min, titrated to 2 μg/min) was administered in combination with anti-PSH medication regimen, and the patient's clinical symptoms were relieved. The patient was discharged in a stable condition and had no further episodes of bradycardia at the 3-months follow-up. Conclusion: Paradoxical bradycardia represents an atypical clinical phenotype of post-TBI PSH, likely mediated by an atypical Cushing reflex secondary to fluctuating intracranial pressure elevations during PSH exacerbations. Clinically, for TBI patients with unexplained bradycardia, potential primary causes should be actively explored, with particular attention to monitoring dynamic changes in intracranial pressure.