Nerve Growth Factor-Induced Sensitization of the Sternocleidomastoid Muscle and Its Effects on Trigeminal Muscle Sensitivity and Pain Profiles: A Randomized Double-Blind Controlled Study.

Aims: To investigate whether localized sensitization of the sternocleidomastoid (SCM) muscle using nerve growth factor (NGF) would affect masseter and anterior temporalis muscle sensitivity and pain profiles.

Methods: A total of 28 healthy participants attended two sessions (T₀ and T₁). At T₀, the maximum voluntary occlusal bite force (MVOBF), as well as pressure pain thresholds (PPT), mechanical sensitivity, and referred pain/sensations for the SCM, masseter, and temporalis muscles, were assessed. Participants also completed the Pain Catastrophizing Scale (PCS), the Pain Vigilance and Awareness Questionnaire (PVAQ), and the Neck Disability Index (NDI). After these assessments, 14 participants received an injection of NGF into the SCM, and 14 received an injection of isotonic saline solution. At T₁ (48 hours postinjection), the participants were again submitted to the same evaluations.

Results: NGF caused significant mechanical sensitization in the SCM (P < .025), but not in the masseter or temporalis muscles (P > .208). It also caused significant increases in NDI score (P = .004). No statistically significant differences were found for MVOBF, frequency of referred pain/sensations, or questionnaire scores (P > .248).

Conclusion: These results suggest that 48 hours after localized sensitization of the SCM, the primary response is impairment of neck function, but not jaw function.