Objective: To use the R2 component of nociceptive-specific blink reflex (nBR) to probe the trigeminal nociceptive system and compare chronic tension-type headache (CTTH) patients and healthy controls.
Methods: Thirty patients with CTTH and 30 age- and sex-matched healthy control subjects were included. nBR were evoked by painful electrical pulses (0.5ms duration), delivered by a concentric electrode placed on the left lower forehead close to the supraorbital foramen. The EMG activity in the orbicularis oculi muscles was recorded bilaterally. The electrical stimulus intensities to evoke individual sensory threshold (Is) and pin-prick pain sensation (Ip) were assessed. A fixed stimulation intensity of 1.5x Ip was used to evoke the nBR. The perceived pain intensity of the electrical stimulus (I(BR)) was assessed by the subjects on a 0-10cm visual analogue scale (VAS).
Results: Is did not differ between CTTH patients and controls (P=0.687) but were lower in females than in males (P=0.020). CTTH patients had higher scores on I(BR) than controls (P=0.026). ANOVA showed significantly higher pre-stimulus EMG values in CTTH patients on the left (stimulated) side (P<0.001), whereas there were no differences between males and females (P>0.168). There were no significant differences in the absolute values of the nBR, however CTTH patients had significantly lower values of the normalized root mean square (RMS) (P=0.035) and area under the curve (AUC) (P=0.042) of the nBR on the left side compared with control subjects with no sex-related differences (P>0.070). The onset latencies and duration were not significantly different between CTTH and control subjects or between female and male subjects (P>0.270). There was no significant correlation between any of the BR parameters (RMS, AUC) and clinical characteristics of CTTH (headache intensity and duration) (P>0.163).
Conclusions: The results of the present study did not detect a significantly different blink reflex response in CTTH patients, but suggested that painful electrical stimulation was associated with consistent increases in eye muscle activity on the same side.
Significance: These findings add further information to central nociceptive pathways in CTTH patients.