Pupillary response is one of the most important neurologic indicators of emergency in comatose patients. Although brainstem reflexes can be diminished during a medically induced coma, ciliospinal reflex (CSR) can remain intact or even enhanced. CSR is a reflex pupillary dilation secondary to sympathetic activation, induced by noxious cutaneous stimulation of ipsilateral head, neck or upper trunk. 

A 31-year-old man presented following a motorcycle collision, wherein he was the driver without protective headgear. He was intubated for airway protection with Glasgow Coma Scale of 8. Computed tomography (CT) of the head revealed bifrontal and bitemporal intraparenchymal traumatic hemorrhages with significant cerebral edema, posterior skull and orbital roof fractures with retrobulbar hemorrhages. He underwent hemicraniotomy and external ventricular drain (EVD) placement. Continuous electroencephalography (EEG) demonstrated seizures refractory to multiple antiepileptic medications. Intracranial pressures (ICP) remained elevated despite hyperosmolar therapy, requiring escalation to medically induced coma with pentobarbital. He was noted to have stimulus-induced anisocoria, resembling fixed and dilated left pupil concerning for further elevation in ICP. This led to recurrent imaging and manipulations with pentobarbital bolus dosing despite EVD showing stable ICPs.  Further examination revealed correlation of the transient pupillary changes after noxious stimuli, suctioning or positioning and resolution of anisocoria with prolonged penlight exposure greater than 20 seconds. The pentobarbital was ultimately tapered off with gradual improvement in ICP and overall mental status. 

Augmented ciliospinal reflex in patients in a pentobarbital coma could easily be mistaken for pathologic elevation of intracranial pressure. After craniocervical noxious stimulation, the ipsilateral pupil may appear dilated and nonreactive due to CSR; however, applying prolonged direct light stimulus to the affected pupil will lead to pupillary constriction. Prompt recognition of this entity may lead to avoidance of unnecessary imaging and procedures in a critically neurologically ill patient.