A new look at arthritis management: nociceptive reflex excitability as a pain biomarker

Modulation of the N13 component of the somatosensory evoked potentials in an experimental model of central sensitization in humans

The N13 component of somatosensory evoked potential (N13 SEP) represents the segmental response of dorsal horn neurons. In this neurophysiological study, we aimed to verify whether N13 SEP might reflect excitability changes of dorsal horn neurons during central sensitization. In 22 healthy participants, we investigated how central sensitization induced by application of topical capsaicin to the ulnar nerve territory of the hand dorsum modulated N13 SEP elicited by ulnar nerve stimulation. Using a double-blind placebo-controlled crossover design, we also tested whether pregabalin, an analgesic drug with proven efficacy on the dorsal horn, influenced capsaicin-induced N13 SEP modulation. Topical application of capsaicin produced an area of secondary mechanical hyperalgesia, a sign of central sensitization, and increased the N13 SEP amplitude but not the peripheral N9 nor the cortical N20-P25 amplitude. This increase in N13 SEP amplitude paralleled the mechanical hyperalgesia and persisted for 120 min. Pregabalin prevented the N13 SEP modulation associated with capsaicin-induced central sensitization, whereas capsaicin application still increased N13 SEP amplitude in the placebo treatment session. Our neurophysiological study showed that capsaicin application specifically modulates N13 SEP and that this modulation is prevented by pregabalin, thus suggesting that N13 SEP may reflect changes in dorsal horn excitability and represent a useful biomarker of central sensitization in human studies.

TNF-α concentrations in pre-operative synovial fluid for predicting early post-operative function and pain after fast-track total knee arthroplasty

BACKGROUND

Tumor necrosis factor-alpha (TNF-α) helps regulate neuroinflammation and anxiety and could conceivable predict early post-operative pain and function after fast-track total knee arthroplasty (TKA).

METHODS

In patients with severe osteoarthritic knees undergoing TKA, we assessed: the correlations between pre-operative concentrations of TNF-α in synovial fluid; pre- and six-week post-operative knee function and pain; pre- and post-operative anxiety; pre- and post-operative synovial fluid concentrations of cartilage oligomeric matrix protein (COMP); age and body mass index (BMI).

RESULTS

Of 100 enrolled patients, 78 had evaluable TNF-α data, and 58 had evaluable COMP data. Pre-operative TNF-α concentrations were inversely correlated with post-operative pain scores during walking (r_S=-0.26, P=0.03) and with change of pain at rest during six weeks after TKA (r_s=-0.28, P=0.03) and were directly correlated with a higher post-operative Knee Society score (KSS) (r_S=0.43, P<0.001) and with greater increases in this score during six weeks after TKA (r_S=0.33, P=0.001). Mean TNF-α concentrations were higher in the 39 patients reporting any pre-operative pain at rest than in 36 patients reporting no pre-operative pain (P=0.015) and were the only independent predictor of pre-operative pain at rest (OR=13, P=0.02). Independent predictors of better post-operative knee function were higher log-transformed TNF-α concentrations (β=0.38, P=0.002) and male sex (β=0.28, P=0.02).

CONCLUSIONS

High levels of pre-operative TNF-α concentrations could be used as an independent predictor of better knee function at six weeks of follow-up. In patients with lower pre-operative TNF-α concentrations, post-operative pain management may improve the early outcome of the operated joint.