MONTREAL — Almost one fifth of patients with chronic knee osteoarthritis may have symptoms of neuropathic pain, requiring consideration of an alternative approach to their pain management, Dr. Jacqueline Hochman said at the World Congress on Osteoarthritis.
“In clinical practice, neuropathic pain is generally not considered a feature of osteoarthritis, and among osteoarthritis researchers it is a novel concept,” she said in an interview. “But a growing body of literature suggests that one reason for treatment failure in osteoarthritis might be a mismatch between the current medications we're using and the underlying mechanisms of pain.”
Dr. Francis Berenbaum agreed in an interview. The research on the pathophysiology of pain in OA has long been neglected in basic as well as clinical research. Recently, novel studies showed that pain in OA can be split up into different entities.
Although this new vision on OA pain has not been fully deciphered, neuropathic pain can now be considered in a subgroup of patients, those with chronic pain, leading to central sensitization, said Dr. Berenbaum, president of the Osteoarthritis Research Society International and head of rheumatology at Pierre and Marie Curie University, Paris.
The 2009 annual OARSI meeting gave experts in the field the opportunity to to explain why this new aspect of OA pain is critical, especially given the availability of specific drugs targeting neuropathic pain, he said.
Dr. Hochman, a rheumatologist at Women's College Hospital in Toronto, explained that current theories about pain point to the possible development of neuropathic pain as a result of the chronic, nociceptive stimulation associated with osteoarthritis. “Most likely, central sensitization in osteoarthritis arises from chronic or recurrent stimulation of peripheral nociceptors, leading to modifications in the central nervous system that cause hyperexcitability in the spinal cord and, perhaps, supraspinal centers involved in the central transmission of pain,” she said.
The diagnosis of neuropathic pain is a clinical one that is “based on a characteristic symptom profile that includes spontaneous sensations such as burning pain, numbness, and tingling, and evoked sensations such as sensitivity to light touch,” she said. In the presence of these symptoms, sensory abnormalities on physical examination, such as pinprick hyperalgesia and allodynia, can aid the diagnosis.
However, there is a paucity of data on symptoms of neuropathic pain in OA, she said.
Because symptoms “are going to lead our patients to seek medical care and alert their physicians to the possibility of underlying neuropathic mechanisms, it's important to know whether people with OA have symptoms of neuropathic pain.”
Therefore, in a group of 171 patients (median age, 76 years) with chronic, symptomatic knee osteoarthritis, she administered a modification of the painDETECT questionnaire (mPD-Q) that is designed to distinguish neuropathic from nociceptive pain.
After the exclusion of those with neurologic conditions (neuropathy, sciatica, shingles, postherpetic neuralgia, multiple sclerosis, stroke, and Parkinson's disease), the study identified 19% of patients who had symptoms suggestive of neuropathic pain, she reported. On multivariate analysis, greater pain intensity and chronic hip or back pain with radiation down either leg (but not below the knee) were correlated with higher scores for neuropathic pain (odds ratio, 3.6). “The subgroup of patients with neuropathic pain symptoms may benefit from further evaluation and possibly treatment for neuropathic pain,” she said.
Neuropathic pain medications include anticonvulsants such as gabapentin and pregabalin, and tricyclic antidepressants such as amitriptyline and nortriptyline, which are believed to “disrupt the central pain pathway and impact central reorganization at the higher spinal centers,” said Dr. Hochman. Antidepressants may also alleviate the depression, anxiety, and sleep disturbances that often accompany—and can also amplify—pain.
Dr. Roy Altman noted that Dr. Hochman is documenting something that many clinicians have long suspected, namely that neuropathic pain plays a role as a part of the pain syndrome in osteoarthritis as a consequence of central pain sensitization.
This information is useful in supporting the use of medications that are not typically considered for osteoarthritis. Since older studies have not documented the value of gabapentin and pregabolin in unselected patients with osteoarthritis, it appears that some benefit could be achieved in selected patients with symptoms compatible with neuropathic pain, according to Dr. Altman, professor of rheumatology at the University of California, Los Angeles.
Additional study of this selected population seems to be in order. Also, more recent research has suggested that in a more general population, serotonin norepinephrine reuptake inhibitors are of value in osteoarthritis, he added.
The congress was sponsored by the Osteoarthritis Research Society International.
Dr. Hochman said she had no conflicts of interest.
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