A physical therapist uses a goniometer to test a patient’s range of motion.
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Pain is the main reason patients with osteoarthritis (OA) seek medical help because of the substantial burden it imposes and its impact on quality of life. Pain can actually change the way the central nervous system works. This central sensitization results in more pain with less provocation. And according to results from an observational study of hospitalized patients with hand OA in Norway, sensitization is independently related to the severity of pain experienced by people with hand osteoarthritis (OA), no matter their psychological profile or radiographic disease severity.
The research involved the largest group—282 patients—to date to be studied for the link between pressure pain thresholds and the degree of pain in the disease. Researchers used temporal summation (i.e., a measure of an increasing pain response due to repetitive painful stimuli) to assess central sensitization, in which heightened neural signaling in the spinal cord and brain brings about a greater pain sensitivity to stimuli.
The Details
This study was an attempt to examine sensitization and pain severity in hand OA patients in a large sample.
Researchers tested pressure pain thresholds at diseased sites to assess patients for peripheral or central sensitization, or both, and pressure pain thresholds at distant, non-painful sites to assess for central sensitization. Patients were divided into tertiles by gender, mindful of pain threshold differences between genders. To measure temporal summation, probes of increasing weights were used. The first to elicit a pain response was used for the test, and pain ratings were recorded over the course of repeated probe applications.
On the numerical rating scale of hand pain in the last 24 hours, pain severity was reported by 32% of patients to be above the acceptable level. On the Australian/Canadian Osteoarthritis Hand Index (AUSCAN), pain was above the acceptable level for 52% of patients.
Researchers found that those with the lowest pressure pain thresholds reported higher numerical rating scale scores—a one-point difference on a 0–10 range test for painful finger joints and a 1.2-point difference in non-painful finger joints—than those with the highest thresholds.
After adjustments, an independent association between pain threshold and pain severity was found only on numerical rating scale scores—with a ß coefficient (i.e., a measure of sensitivity) of 0.9 [95% CI 0.2, 1.6] for painful finger joints and 1.1 [95% CI 0.5, 1.8) for non-painful joints. No independent association was found for pain severity measured on the AUSCAN.
The researchers also found that pressure pain thresholds at distant body sites, such as the wrist and trapezius muscle, had significant independent associations with pain severity on the numerical rating scale for measurements taken at the wrist and trapezius muscle.
Researchers found that temporal summation, demonstrating central sensitization, was present in 42% of patients. Those patients reported numerical rating scale scores an average of one point higher than those without temporal summation, researchers said. After an adjusted analysis, an association between temporal summation and pain severity was found only for the numerical rating scale, not the AUSCAN.
What This Means
Dr. Steen Pettersen
Dr. Steen Pettersen says the findings—including the high prevalence of temporal summation—indicate that pain sensitization contributes to the complex experience of pain in hand osteoarthritis.
“This is interesting as we struggle in explaining to patients why their joints and hands hurt,” she says. “We can’t simply look at their radiographs, clinical swelling or ultrasound findings and predict their pain. Some patients experience a great amount of pain in the absence of severe joint pathology.”
The findings stand out from previous work on the topic, she says, because of the wide range of disease severity in the study population, making the results more generalizable. Adjustments for confounders ranged from social and psychological factors to age, sex and body mass index.
She says the findings point to increasing relevance for potentially mapping and phenotyping pain using sensitization data. In the future, clusters of patients with certain phenotypes may be found to be more suitable for central-acting agents or to cognitive behavioral coping strategies.
“OA pain and its heterogeneity have made pain phenotypes an important subject,” Dr. Steen Pettersen says. “I believe we still do not have enough knowledge to be able to make mechanistic pain phenotypes, but more and more evidence is pointing at a useful (role for) pain phenotyping.”
She says follow-up data are needed to explore how values seen in quantitative sensory testing change or don’t change over time and, in OA, how changes in pain sensitivity can predict worsening of hand OA.
“Another step is to explore how comorbidities, social and psychological factors relate to pain sensitization in hand OA,” Dr. Steen Pettersen says. “And finally, as quantitative sensory testing of pain sensitivity is quite new in OA research, we need more data supporting its feasibility and reproducibility.”
Dr. Kumar
Bharat Kumar, MD, clinical assistant professor of immunology at the University of Iowa, calls the findings “important and thought provoking.
“Osteoarthritis is classically thought about as a ‘wear-and-tear’ arthritis due to largely local mechanical issues,” he says. “The findings that patients with hand osteoarthritis have more widespread pain due to central pain sensitization complicates the story. From a research standpoint, it opens up avenues for further research about the neurological and inflammatory aspects of OA pain.”
Dr. Kumar says the findings from this study should prompt physicians to “start seeing hand osteoarthritis as a systemic disease that needs to be treated in a multi-modal manner, similar to fibromyalgia.”
Patients should not only be prescribed physical therapy, Dr. Kumar says, but steps to minimize pain sensitization should be taken. These can include keeping healthy sleep habits, exercising, following a healthy diet and addressing psychosocial factors, such as anxiety, depression and isolation.
“Unfortunately, our understanding of this phenomenon is still very incomplete,” he says. “More research is needed to see if these steps can specifically reduce the pain of osteoarthritis, but they have been helpful in other conditions defined by central pain sensitization, such as fibromyalgia.”
Thomas R. Collins is a freelance writer living in South Florida.
Reference
- Pettersen PS, Neogi T, Magnusson K, et al. Peripheral and central sensitization of pain in individuals with hand osteoarthritis and associations with self-reported pain severity. Arthritis Rheumatol. 2019 Jul;71(7):1070–1077.
