Abstract 17: A novel microanalytical technique for assaying soft tissue demonstrates significant quantitative biochemical differences in 3 clinically distinct groups: normal, latent, and active.

Objectives: To determine (1) whether a novel microdialysis needle can successfully sample the biochemical milieu of trigger point 1 (TP1) in the upper trapezius muscle in healthy subjects and (2) whether there are measurable differences among those with symptoms and physical findings related to myofascial trigger points (MTrPs). Design: Prospective, controlled trial. Setting: Biomedical research hospital. Participants: 3 subjects were selected based on history and physical examination for 3 groups (N=9): group 1, normal (no neck pain, no MTrP); group 2, latent (no neck pain, MTrP present); and group 3, active (neck pain, MTrP present). Intervention: Pressure algometry was performed at TP1 to determine pain pressure threshold (PPT). Samples were obtained continuously with a microdialysis needle at regular intervals, starting with needle insertion, elicitation of a local twitch response, and then posttwitch. Main Outcome Measures: PPT and levels of pH, substance P, calcitonin gene-related peptide (CGRP), bradykinin, norepinephrine, tumor necrosis factor-alpha (TNF_α), and interleukin-1β (IL-1β). Results: The active group had a lower PPT (P<.08). Overall, the amount of substance P, CGRP, bradykinin, norepinephrine, TNF_α, and IL-1β was significantly higher in the active group than in the other 2 groups (P<.01). Overall, pH was significantly lower in the active group than in the other 2 groups (P<.03). At 5 minutes, peak levels of substance P and CGRP differed significantly in all 3 groups (3>2>1, P<.02). Conclusions: This technique recovered extremely small quantities (<0.5μL) of very small substances (molecular weight, <100kd) directly from soft tissue. There were significant differences in the levels of pH, substance P, CGRP, bradykinin, norepinephrine, TNF_α, and IL-1β in those subjects with an active MTrP (symptoms, MTrP present) compared with subjects with a latent MTrP (no symptoms, MTrP present) and normal subjects (no symptoms, no MTrP).