Conditioned Pain Modulation Decreases Over Time in Patients With Neuropathic Pain Following a Spinal Cord Injury

Abstract

Background Neuropathic pain is a major problem following spinal cord injury (SCI). Central mechanisms involved in the modulation of nociceptive signals have been shown to be altered at the chronic stage, and it has been hypothesized that they might play a role in the development of chronic pain. Objective This prospective longitudinal study aimed to describe the evolution of pain modulation mechanisms over time after SCI, and to explore the relationships with the presence of clinical (neuropathic and musculoskeletal) pain. Methods Patients with an SCI were assessed on admission (n = 35; average of 38 days postinjury) and discharge (n = 25; average of 131 days postinjury) using the International Spinal Cord Injury Pain Basic Data Set. Conditioned pain modulation was assessed using the cold pressor test (10 °C; 120 s) as the conditioning stimulus and tonic heat pain, applied above the level of injury, as the test stimulus (120 s). Heat pain threshold was also assessed. Results A marked decrease in the efficacy of conditioned pain modulation was observed over time, with 30.2% of inhibition at admission and only 12.9% at discharge on average ( P = .010). This decrease was observed only in patients already suffering from neuropathic pain at admission and was not explained by a general increase in sensitivity to thermal nociceptive stimuli. Conclusion These results suggest that the presence of neuropathic pain leads to a decrease in conditioned pain modulation over time, rather than supporting the hypothesis that inefficient conditioned pain modulation mechanisms are leading to the development of neuropathic pain.

Does Conditioned Pain Modulation Predict Pain Outcomes?

“…In a prospective longitudinal study of 35 patients with spinal cord injury, a decrease in the efficacy of CPM was observed over time only in patients already suffering with neuropathic pain at admission 32. The results suggest that neuropathic pain leads to inefficiency of the CPM response, rather than CPM inefficiency as a risk factor for the development of neuropathic pain.…”

Does the painDETECT questionnaire identify impaired conditioned pain modulation in people with musculoskeletal pain? – a diagnostic accuracy study

“…Conditioned pain modulation is a predictor in developing and treating neuropathic pain [ 44 ] but may perform dissimilarly in neuropathic pain conditions. Gagné et al suggested that the presence of neuropathic pain leads to a decrease in conditioned pain modulation over time [ 45 ]. Carpal tunnel syndrome [ 13 ] and painful peripheral neuropathy [ 15 ] are examples of impairment of conditioned pain modulation.…”

Medial Prefrontal Transcranial Direct Current Stimulation Aimed to Improve Affective and Attentional Modulation of Pain in Chronic Low Back Pain Patients

“…In line, the largest CPM magnitudes were observed in the absolute first session with, albeit non-significantly, less CPM observed in each subsequent session. Recently, there has been a tendency for studies to report a lack of significant improvement in CPM despite reduction or even resolution of pain [ 38 , 39 ], and in some cases temporal reduction in CPM with repeated assessments during the development of chronic pain [ 40 , 41 ]. Less is known about reductions in the efficacy of attentional and affective paradigms to modulate pain, as these are often performed in single session studies, but these manipulation effects are also likely to be impacted by stimulus and contextual novelty [ 42 ].…”