Cutaneous heat and light-induced pain thresholds in post-traumatic headache attributed to mild traumatic brain injury.

OBJECTIVE: The purpose of this study was to characterize cutaneous heat and light-induced pain thresholds in people with post-traumatic headache (PTH) compared with healthy controls (HCs).

BACKGROUND: Photophobia and allodynia are common in PTH, and there is emerging evidence to support multimodal sensory dysfunction.

METHODS: In this age- and sex-matched cohort study, individuals with PTH (n = 20) and HCs (n = 20), aged 18-65 years, were recruited from an institutional database of research volunteers, from the concussion clinic, and via the use of approved flyers posted on the Mayo Clinic Campus in Scottsdale, Arizona. Participants were assessed using the Allodynia Symptom Checklist (ASC-12), Photosensitivity Assessment Questionnaire (PAQ), State Trait Anxiety Inventory (STAI), and Beck Depression Inventory (BDI). Quantitative sensory testing quantified heat pain thresholds. A light stimulation device quantified light-induced pain thresholds. Subsequently, heat pain thresholds were obtained immediately, 10, and 40 min after a bright light stressor.

RESULTS: The mean photophobia symptom severity score, based on the PAQ, was higher in participants with PTH compared with HCs, mean 0.62 (SD = 0.25) versus mean 0.24 (SD = 0.24), p < 0.001. Light-induced pain thresholds were lower in participants with PTH (median = 90.5 lux and quartiles = 17.8 to 378.5) compared with HCs (median = 863.5 lux and quartiles = 519.9 to 4906.5) and were independent from BDI and STAI (p < 0.001). Allodynia scores did not differ between participants with PTH and HCs after adjusting for BDI and STAI scores. Baseline forehead heat pain thresholds were not different, participants with PTH mean 41.9°C (SD = 0.89) versus HCs mean 44.3°C (SD = 0.89), p = 0.061; however, forearm heat pain thresholds were lower in participants with PTH compared with HCs, mean 40.8°C (SD = 0.80) versus mean 44.4°C (SD = 0.80), p = 0.002. The forehead heat pain threshold change from baseline post bright light stressor in participants with PTH versus HCs was different immediately (mean -1.2 (SD = 0.53), p = 0.025), 10 min (mean -1.8 (SD = 0.74), p = 0.015), and 40 min (mean -1.8 (SD = 0.88), p = 0.047). The forearm heat pain threshold change immediately post bright light stressor in participants with PTH versus HCs was different, mean -1.9°C (SD = 0.58), p = 0.001, however, not different at 10 and 40 min.

CONCLUSIONS: Photophobia is higher and light-induced pain thresholds are lower in participants with PTH. Exposure to a light stressor reduced heat pain thresholds in participants with PTH immediately post bright light stressor, but not in HCs. This study provides evidence for multimodal sensory dysfunction in people with PTH.