Application of the IASP grading system for 'nociplastic pain' in chronic pain conditions: A field study

The concept nociplastic pain has been developed for patients in whom clinical and psychophysical findings suggest a predominant central sensitization type of pain that is not fully explained as nociceptive or neuropathic. Here we tested, how well the recently published grading system differentiates between chronic primary pain or chronic secondary pain conditions. We recruited patients with Fibromyalgia (FMS, 41), Complex Regional Pain Syndrome (CRPS, 11), Osteoarthritis (OA, 21) or Peripheral Nerve Injury (PNI, 8). We used clinical history, pain drawings, Quantitative Sensory Testing (QST) and questionnaires to classify patients' pains as possibly or probably nociplastic in nature. All FMS and CRPS patients exhibited widespread or regional pain that was not explainable by nociceptive nor neuropathic mechanisms. Widespread pain in 12 OA patients was fully explained as nociceptive and regional pain in 4 PNI patients as neuropathic in all but one in each group. QST provided evidence for hypersensitivity in 9/11 CRPS patients but only 27/41 FMS patients (possible nociplastic pain). 82% of the CRPS patients but only 54% of FMS patients reported a history of hypersensitivity and mental comorbidities (probable nociplastic pain). We suggest that clinical examination of hypersensitivity should be done in more than one region and that adding a high tender point count as evidence for hypersensitivity phenomena may be useful. Further we suggest to switch the sequence of steps so that self-reported hypersensitivity and comorbidities come before clinical examination of hypersensitivity; Since the nociplastic pain concept calls for brainstem and cortical plasticity we discuss in detail potential measurement strategies.