The aim of this present study was to test the hypothesis that tonic nociceptive stimulation of latent myofascial trigger points (MTPs) may induce a spatially enlarged area of pressure
pain hyperalgesia. Painful
glutamate (.2 mL, 1M) stimulation of latent MTPs and non-MTPs in the forearm was achieved by an electromyography-guided procedure.
Pain intensity (as rated on the visual analog scale [VAS]) and
referred pain area following
glutamate injections were recorded. Pressure pain threshold (PPT) was measured over 12 points in the forearm muscles and at the mid-point of tibialis anterior muscle before and at .5 hour, 1 hour, and 24 hours after
glutamate injections. The results showed that maximal
pain intensity, the area under the VAS curve, and
referred pain area were significantly higher and larger following
glutamate injection into latent MTPs than non-MTPs (all, P < .05). A significantly lower PPT level was detected over time after
glutamate injection into latent MTPs at .5 hour (at 4 points), 1 hour (at 7 points), and 24 hours (at 6 points) in the forearm muscles. However, a significantly lower PPT was observed only at 24 hours after
glutamate injection into non-MTPs in the forearm muscles (at 4 points, P < .05) when compared to the pre-injection PPT. PPT at the mid-point of the tibialis anterior was significantly decreased at 1 hour only as compared to the pre-injection PPT in both groups (< .05). The results of the present study indicate that nociceptive stimulation of latent MTPs is associated with an early onset of locally enlarged area of
mechanical hyperalgesia.
PERSPECTIVE: This study shows that MTPs are associated with an early occurrence of a locally enlarged area of pressure
hyperalgesia associated with spreading central sensitization. Inactivation of MTPs may prevent spatial
pain propagation.