Application of the grading system for "nociplastic pain" in chronic primary and chronic secondary pain conditions: a field study.

The concept "nociplastic pain" has been developed for patients with features of nociceptive system sensitization that are not explained as nociceptive or neuropathic. Here, we tested how well the recently published grading system differentiates between chronic primary and secondary pain conditions. We recruited patients with fibromyalgia (FMS, n = 41), complex regional pain syndrome (CRPS, n = 11), osteoarthritis (OA, n = 21), or peripheral nerve injury (PNI, n = 8). We used clinical history, pain drawings, quantitative sensory testing (QST), and questionnaires to classify their pains as possibly or probably "nociplastic." All patients with chronic primary pain exhibited widespread/regional pain not explainable by either nociceptive or neuropathic mechanisms. Widespread pain occurred in 12 patients with OA but was identified as nociceptive in 11 of 12. Regional pain occurred in 4 patients with PNI but was identified as neuropathic in 3 of 4. At this step, the grading system had 100% sensitivity and 93% specificity. Clinical evidence for pain hypersensitivity by QST, and history of hypersensitivity and mental comorbidities did not differentiate between chronic primary pain (QST: 36/52 = 69%, history: 43/52 = 83%) and secondary pain conditions (QST: 20/29 = 69%, history: 24/29 83%). Based on these data, specificity remained excellent (93%), but sensitivity dropped substantially (60%) due to lacking evidence for pain hypersensitivity in many patients with FMS. This low sensitivity suggests that the published grading system is not suitable for screening purposes. We suggest structural and content modifications to improve sensitivity, including placement of patient history before clinical examination and addition of a high tender point count as evidence for widespread pain hypersensitivity.