Neuropathic pain phenotype identified in knee osteoarthritis

By Lucy Piper, Senior medwireNews Reporter

Some patients with knee osteoarthritis (OA) may experience neuropathic-like symptoms associated with central pain processing, reflecting a discrete phenotype, study findings suggest.

The results also showed that the painDETECT and Self-report Leeds Assessment of Neuropathic Symptoms and Signs (S-LANSS) questionnaires may be able to assess the pain quality associated with this phenotype.

Among 192 participants with knee OA who responded to both questionnaires, painDETECT categorised neuropathic pain in 27% and S-LANSS in 30%, based on cut-off scores of at least 19 and 12, respectively.

Despite classifying neuropathic pain in similar proportions of patients, agreement in classifications was only fair, at 74%.

Rasch analysis indicated that painDETECT was a better measurement scale for neuropathic-like symptoms, displaying a good fit to the Rasch model with the removal of one item and was relatively well targeted to the sample.

By contrast, the S-LANSS fit was poorer, with the scale less able to discern distinct strata within the sample. It was also less reliable and not as targeted, note researcher Nadina Lincoln (University of Nottingham, UK) and co-workers.

Nevertheless, the two measures were more closely associated with each other than with measures of pain severity and remained strongly correlated after controlling for pain severity. The researchers therefore say it is too soon to know which measure may best predict treatment outcome.

“Both questionnaires appear to address a coherent phenotype in people with knee OA, despite aforementioned differences in pain classifications”, the team comments in Arthritis Care & Research. This discrete phenotype reflects pain quality as distinct from pain severity, they add.

While the symptoms measured were suggestive of neuropathy, the team found in a separate sample of 70 patients with knee OA that high painDETECT scores were significantly associated with low pain pressure thresholds across different body sites after adjusting for pain severity, suggesting central pain processing.

“Central processing may augment pain severity and contribute to overlapping pain qualities associated with either nerve or joint damage”, the researchers explain.

It therefore remains uncertain whether knee OA leads to neuropathology, alterations in central pain processing lead to pain characteristics shared with neuropathic pain or if some people are predisposed to knee OA with neuropathic symptomatology, they note.

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