Quantitative Sensory Testing May Predict Treatment Outcomes
LAS VEGAS—“If not now, at some point in the near future, there will be some clinical utility for quantitative sensory testing (QST),” said Roger B. Fillingim, PhD, Professor, College of Dentistry, and Director of Pain Research and Intervention, Center of Excellence at the University of Florida, Gainesville.
He defined QST as “the assessment of perceptual and/or physiological responses to systematically applied and quantifiable sensory stimuli for the purpose of characterizing somatosensory function or dysfunction.”
Noting that the purpose of diagnosis is to guide treatment and prognose, Dr. Fillingim, also President of the American Pain Society, used as an example a patient with back pain of 6 months' duration. After taking a history and conducting a physical examination and diagnostic tests, “how confident are clinicians about the mechanisms driving pain?” he asked.
The current problem: “pain diagnosis is based primarily on signs and symptoms, sometimes combined with evidence of structural damage; however, the diagnosis typically provides limited information regarding the mechanisms underlying the pain experience.” Yet, “every treatment we apply impacts some mechanism that is hopefully related to pain,” he said.
Dr. Fillingim said methods for identifying pain mechanisms in humans—which can include psychological factors—are diagnostic tests to identify peripheral generators (eg, skin biopsies for small fiber neuropathy), pharmacologic approaches, distinct symptom clusters in patients with the same diagnosis, genetic markers, brain imaging, and QST.
QST can help identify pain mechanisms by revealing individual differences in pain, show case-control differences in pain processing, and can be used to sub-group patients. In addition, QST responses may predict future pain as well as predict treatment responses (see Table).
The concept of mechanism-based pain is not new, he said. Dr. Fillingim enumerated different approaches to QST, such as tuning fork, two-point discrimination, cotton swab test, monofilament test, palpation, and straight leg raise. He also described current findings regarding the application of QST to chronic pain and its treatment.
Simple QST procedures can be easily implemented in the clinical setting, said Dr. Fillingim, who advised attendees to “start today, track changes over time, and use a novel behavioral sample to gain clinical experience.”
What's still needed, he concluded, are normative values and clinical QST modules that have been well tested. Finally, to date, reimbursement issues prohibit using more sophisticated and comprehensive QST batteries in most settings.