Cholinergic dysfunction in cognitive impairments after aneurysmal subarachnoid hemorrhage

OBJECTIVE: Although cognitive impairments have been observed after subarachnoid hemorrhage (SAH), little is known about their neurobiological bases. To examine cholinergic function in such patients, we used a known test for Alzheimer's disease based on an exaggerated pupil dilation response to a cholinergic antagonist, tropicamide (the tropicamide drop test). METHODS: Seventeen patients who were treated surgically after aneurysmal SAH were divided into two groups on the basis of their scores on the Mini-Mental State Examination (MMSE): Group A (MMSE≥28) and Group B (MMSE<27). The mean interval of time between surgery and administration of the MMSE was 4.7 ± 2.1 years for Group A and 4.2 ± 1.3 years for Group B. The tropicamide drop test was performed within 1 month after the MMSE for each patient. After measurement of the baseline pupil diameter (R1, right pupil size: L1, left pupil size), one drop of 0.01% tropicamide was applied to the right eye and physiological saline to the left eye. Pupil diameter (R2, right pupil size; L2, left pupil size) was then remeasured. Data were represented as the dilation ratio of the right pupil (R2/R1) and as the relative dilation ratio of the right pupil to that of the left pupil (R2L1/R1L2). RESULTS: The mean dilation ratio of the right pupil (R2/R1) was higher in Group B (1.13 ± 0.09) than in Group A (1.07 ± 0.11), although the difference did not reach statistical significance (P = 0.18). The relative dilation ratio (R2L1/R1L2) was significantly higher in Group B (1.41 ± 0.36) than in Group A (1.06 ± 0.20) (P < 0.05). CONCLUSION: We determined cholinergic dysfunction in patients with cognitive impairment after SAH on the basis of the pupillary response to tropicamide. The results provide an insight into the pathophysiology of cognitive impairments after SAH, which might lead to future treatment strategies.