Do diagnostic blocks have beneficial effects on pain processing?

Background And Objectives: Diagnostic blocks of cervical zygapophysial joints have been used as part of the management strategy for patients with chronic neck pain. Little information is available regarding the sensory processing changes that occur after these common procedures. In a hypothesis-generating prospective study, the pressure-pain thresholds, electrical pain thresholds, and descending inhibitory modulation response using the conditioned pain modulation paradigm are described for 9 patients with cervical zygapophysial joint pain that underwent successful comparative diagnostic blocks.

Methods: The study was designed as a prospective cross-sectional study in 9 patients with cervical zygapophysial joint pain with positive comparative diagnostic blocks using lidocaine and bupivacaine. Each patient underwent baseline Quantitative Sensory Testing (QST) measurement (QST 1) after inclusion. Subsequent QST measurements (QST 2 and 3) were performed only after comparative blocks proved positive and only after the neck pain returned after each diagnostic block.

Results: Despite the return of their neck pain after the local anesthetic agents wore off, the patients exhibited (1) less focal pressure hyperalgesia, (2) generalized electrical hypoalgesia, and (3) significantly reduced conditioned pain modulation responses.

Conclusions: Our preliminary evidence suggests that the perturbations to the sensory processing system from effective diagnostic blocks affect the tonic inhibitory system in a positive manner. Conditioned pain modulation, however, needs to be interpreted in the context of altered pain thresholds, and future studies should aim to investigate the shift in the nociceptive balance between facilitatory and inhibitory control after therapeutic interventions.