Side of pupillary mydriasis predicts the cognitive prognosis in patients with severe traumatic brain injury

Background Pupils' abnormalities are associated to bad prognosis in traumatic brain injury. We investigated the association between the side of pupil mydriasis and the long‐term cognitive performance of patients with severe traumatic brain injury (TBI). Methods We analyzed the cognitive performance of patients admitted at the intensive care unit with isochoric pupils (IP, n = 28), left mydriasis (LM, n = 10), right mydriasis (RM, n = 9) evaluated in mean 2.5 years after the severe TBI and controls (n = 26) matched for age, sex and education level. Results Patients and controls had similar scores in the four WAIS‐III investigated subtests. In comparison with controls, LM patients had lower scores in Letters and Category Fluency and IP patients in Category Fluency. Among the 10 evaluated memory tests, LM patients had lower scores than controls in eight, RM patients in two and IP in three memory tests. IP and RM were 3.5 to nine times more associated to significant impairment (cognitive scores under the percentile 10 of controls) in six of 16 investigated cognitive tests. LM was six to 15 times more associated to significant impairment in 10 of 16 cognitive tests. The association among the pupil abnormalities and cognitive performances remained significant after the multiple linear regression analysis controlling for age, gender, admission coma Glasgow scale and serum glucose, presence of associated trauma, and cranial computed tomography abnormalities. Conclusion Side of admission pupil abnormalities may be a useful variable to improve prognostic models for long‐term cognitive performance in severe TBI patients.