The relationship between pupillary light reflex and clinical measures of central pain processing in chronic WAD. An observational study with healthy cohort comparison.

BACKGROUND

Autonomic dysregulation has previously been reported in chronic whiplash-associated disorders (WAD). Autonomic function can be evaluated via the pupillary light reflex (PLR).

OBJECTIVE

To determine if PLR measures differ between chronic WAD and healthy controls (HCs), and to investigate the relationship between a) PLR and clinical measures associated with central pain processing, and b) psychological measures - posttraumatic stress, anxiety and stress - associated with autonomic nervous system (ANS) function.

DESIGN

Observational study with healthy control comparison.

PARTICIPANTS

Twenty-six patients with chronic WAD and 26 age/sex-matched HCs (58% female).

OUTCOME MEASURES: Independent t-tests compared WAD and HC participants. Correlation analyses investigated the association between PLR and clinical measures of central pain processing (Central Sensitization Inventory, cervical and tibialis anterior pressure pain thresholds, temporal summation and conditioned pain modulation), and psychological measures (Depression, Anxiety, and Stress Scale and the PTSD Checklist for the DSM-5) evaluating posttraumatic stress, anxiety and stress symptoms.

RESULTS

For PLR measures, participants with chronic WAD demonstrated significantly reduced pupil constriction amplitude (Mean difference [95%CI]: 0.33 mm [0.08, 0.58]; p = 0.01) and quicker time to return to 75% of resting pupil diameter during re-dilation (Mean difference [95%CI]: 0.39secs [0.08, 0.58]; p = 0.01), indicative of parasympathetic and sympathetic nervous system dysfunction. Pupillometry measures were not related to measures of central pain processing but instead related to stress or anxiety symptoms.

CONCLUSIONS

People with chronic WAD demonstrated changes in PLR, indicative of possible autonomic dysregulation. There was no relationship to measures of central pain processing. However, psychological measures were associated with pupillometry, suggesting a potential interaction between autonomic function and psychological manifestations in chronic WAD. The direction of this relationship warrants further investigation.