PLOS Medicine has featured a novel method of identifying pain subtypes that separates radicular from axial lower back pain (LBP).

The tool, based on a structured interview (16 questions) and a standardised bedside examination (23 tests), was tested on 130 patients with peripheral neuropathic pain caused by diabetic polyneuropathy, postherpetic neuralgia, or radicular low back pain (LBP), and in 57 patients with non-neuropathic (axial) LBP.

A cluster analysis revealed distinct pain subtypes that characterized six subgroups of patients with neuropathic pain and two subgroups of patients with non-neuropathic pain. Using a classification tree analysis, the researchers indentified the most discriminatory assessment items for the identification of pain subtypes and combined these six interview questions and ten physical tests in a pain assessment tool called Standardized Evaluation of Pain (StEP).

StEP was then validated for the distinction between radicular and axial LBP in an independent group of 137 patients. StEP identified patients with radicular pain with high sensitivity (92%; 95% confidence interval [CI] 83%–97%) and specificity (97%; 95% CI 89%–100%) and exceeded that of a dedicated screening tool for neuropathic pain and spinal magnetic resonance imaging. The researchers were also able to reproduce subtypes of radicular and axial LBP, underscoring the utility of StEP for discerning distinct constellations of symptoms and signs.