Adding a protocol to the standard tests used by physicians to diagnose fibromyalgia may improve the likelihood that the disorder will be diagnosed more accurately, a new study shows.
Results of the study that makes recommendations about also measuring slowly repeated evoked pain response (SREP) — a progressive increase in perceived pain in response to slow, repeated pressure stimuli — were published in the journal Pain Medicine. It is titled “Addition of Slowly Repeated Evoked Pain Responses to Clinical Symptoms Enhances Fibromyalgia Diagnostic Accuracy.”
Although the causes of fibromyalgia are currently unknown, some studies have suggested the disorder arises from a sensitization process taking place in the central nervous system (CNS, the brain and spinal cord). Sensitization refers to a phenomenon in which a repeated stimulus, such as pain, triggers a progressively stronger response of nerve cells in the CNS.
Neuroimaging studies have shown that patients with fibromyalgia experience sensitization in response to evoked pain, such as pressure or very cold water. Evoked pain is typically measured by analyzing a patient’s pain threshold and tolerance.
However, studies focused on evaluating the relationship between static evoked pain measures and a clinical diagnosis of fibromyalgia have yielded inconclusive findings. In addition, due to their static nature, pain threshold and tolerance may not be the best parameters to capture CNS sensitization that is thought to underlie fibromyalgia.
In contrast, “a novel dynamic evoked pain index based on the increase in pain perception due to slowly repeated evoked pain (SREP) has been shown to be especially sensitive to pain sensitization in [fibromyalgia] patients,” the researchers wrote.
SREP sensitization is defined as the progressive increase in perceived pain in response to slowly repeated pressure stimulation. Previous studies have shown that SREP can distinguish patients with fibromyalgia from those with chronic pain associated with other diseases (e.g., rheumatoid arthritis) and healthy individuals more accurately than static-evoked pain measures.
That evidence suggests SREP can be a specific marker of central pain sensitization in fibromyalgia. However, whether SREP can enhance the diagnostic accuracy of fibromyalgia beyond the standard evaluation of clinical symptoms has not been investigated yet.
To explore that possibility, a group of researchers at Universidad de Jaén in Spain analyzed SREP responses in 50 patients with fibromyalgia, 30 with rheumatoid arthritis and 50 healthy individuals. In addition to SREP responses, investigators evaluated participants’ clinical pain, fatigue, insomnia, pain catastrophizing (exaggerated negative thoughts brought on by previous painful experiences), and negative mood.
The SREP protocol consisted of a series of nine low-intensity painful pressure stimuli applied to the participants’ fingernails. Each stimulus lasted five seconds, with 30-second intervals between each round.
SREP sensitization was observed among those with fibromyalgia, but not among those with rheumatoid arthritis or in healthy individuals. Essentially, what this meant was that with each round, those with fibromyalgia experienced a progressive increase in pain, even though the same amount of pressure was being applied in all rounds.
Findings also showed that individuals with SREP sensitization were more likely to experience clinical pain, fatigue, insomnia, and pain catastrophizing. However, no associations were identified between SREP and negative mood.
Researchers also found that SREP could be used to distinguish patients with fibromyalgia from those with rheumatoid arthritis and healthy individuals. In fact, a combination of fatigue, insomnia, and SREP led to near perfect diagnostic accuracy (99%) in differentiating fibromyalgia from healthy individuals, and 86.3% accuracy in discriminating fibromyalgia from those with rheumatoid arthritis.
“These results provide further evidence of SREP as a marker of pain sensitization in fibromyalgia and suggest that it captures aspects of fibromyalgia not fully captured by clinical features,” the investigators wrote.
“Combining SREP with assessment of clinical features could potentially improve fibromyalgia diagnosis,” they stated.
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