Referred sensation location can be altered by a strong heterotopic nociceptive stimulus: implications for clinical pain conditions

Referred sensations (RS) are a common clinical phenomenon in patients with musculoskeletal pain; however, the underlying mechanisms of RS and implications for diagnosis and management are poorly understood. The location of referral seems to have a preferred site, but studies have suggested it can be redirected to a site of previous injury and pain. However, it is not known if the same phenomenon can occur for a much shorter-lasting painful stimulus in the trigeminal system. The aim of this study was to assess if RS location elicited with standardized palpation of the masseter muscle could be altered following a 10-minute painful infusion of hypertonic saline into the retromolar region. A total of 56 healthy participants participated in this cross-over study performed in 2 sessions separated by 1 hour. At each session, baseline and postinfusion assessments of masseter muscle mechanical sensitivity were performed using 2 different forces (0.5 kg and 2 kg). Between assessments, hypertonic saline (5%) or isotonic saline (control) were continuously infused into the retromolar region. Participants were asked to rate their mechanical sensitivity and any RS they experienced as well as to draw the location of the RS. No difference in mechanical sensitivity or RS frequency was seen after either infusion when compared with before infusion. However, the RS location was displaced on average 1.2 cm between the baseline and postinfusion assessments for the hypertonic saline infusion, which was significantly increased when compared with the isotonic saline infusion which was on average 0.4 cm. These novel findings indicate the potential to modify the location of RS in the trigeminal system following a relatively brief noxious input. Clinicians need to be aware of the possible rerouting of RS in patients with complex orofacial pain.