Poster 132: Local Biochemical Response and Dynamics of Microdialysis Needle Insertion in Active, Latent and Absent Myofascial Trigger Points

Abstract

Objective: To further differentiate active, latent, and normal myofascial trigger points (MTrPs). Design: Prospective, controlled. Setting: Biomedical research hospital. Participants: 18 subjects were equally distributed into 3 groups based on the following: actives (neck pain and MTrP present in the trapezius muscle), latents (no neck pain, MTrP present), and controls (no pain, no MTrP). Interventions: Samples were obtained at 1-minute intervals following needle insertion. After 4 minutes, samples were obtained every 20 seconds. At 5 minutes, the microdialysis needle was advanced into the MTrP for active and latent subjects, or an equivalent distance for healthy subjects. Main Outcome Measures: To characterize the temporal sequence of a possible inflammatory cascade of selected analytes, we measured inverse proton concentration, bradykinin, serotonin, norepinephrine (NE), substance P, calcitonin gene-related peptide, tumor necrosis factor-alpha, Interleukin-1 beta, Interleukin 6, and Interleukin 8. Data were normalized to initial values and grouped. Times were extrapolated at which 25%, 50%, and 100% of peak concentration values were reached. Results: The 25% peak concentration values of NE in Actives were on average 40 seconds earlier than controls, which approached significant difference (P=0.07). Actives demonstrated the greatest intervals between 25% peak concentration values and 100% PCV. The earliest 25% peak concentration values were for NE and inverse proton concentration in the actives. The 100% peak concentration values of the active group were clustered tightly between 5 and 5.5 minutes. In latents and controls, the time intervals between 25% peak concentration values and 100% peak concentration values were reduced. Twenty-five percent peak concentration values, 50% peak concentration values, and 100% peak concentration values in latents and normals ranged generally between 4.5 and 5.5 minutes. Conclusions: The earlier 25% PCVs of NE and inverse proton concentration in the actives suggests these biochemicals may help initiate a nociceptive cascade unique to active MTrPs. The rapid response to needle insertion in actives suggests hypersensitivity. This study builds on previous work that showed that concentrations of biochemicals associated with pain and inflammation are elevated in actives compared with latents and controls.