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, reported Dr. Jacqueline Hochman 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. 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,” Dr. Hochman 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, Dr. Hochman 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.
Other study measures included biopsychosocial factors, such as depression, anxiety, pain catastrophizing, and sleepiness; sociodemographics; osteoarthritis severity; comorbid conditions; and medication use.
After the exclusion of the patients who had neurologic conditions (neuropathy, sciatica, shingles, postherpetic neuralgia, multiple sclerosis, stroke, and Parkinson's disease), the study identified 19% of the patients who had symptoms suggestive of neuropathic pain, Dr. Hochman 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,” Dr. Hochman said. 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.
Dr. Hochman said that further research is needed to determine whether people with painful osteoarthritis who have symptoms of neuropathic pain respond better to neuropathic treatments vs. standard medications such as NSAIDs and acetaminophen. She said that there is little research to date to guide clinicians on whether to treat both nociceptive and neuropathic pain concomitantly, or whether treatment for neuropathic pain can be stopped if pain improves.
The congress was sponsored by the Osteoarthritis Research Society International.
Dr. Hochman said she had no conflicts of interest.
Many clinicians have long suspected that neuropathic pain plays a role as a part of the pain syndrome in OA.
Source DR. ALTMAN