somatosensory changes, LBP

A four-month study 1 of acute lower back pain (LBP) patients and a pain-free control group found a correlation between persistent LBP and somatosensory changes over time that appeared to increase pain and other types of neurological sensitivity in chronic LBP patients. Because even baseline pain awareness was elevated in the subjects that later developed chronic LBP, the authors of the study suggest further studies that would examine the evident link between heightened pain sensitivity and its possible role in the development of chronic LBP.

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They also suggest patients undergoing initial LBP diagnosis also be evaluated for potential psychological issues that might be contributing factors to their pain.

The Study

Quantitative sensory responses (QSR) were collected and analyzed at less than three weeks prior to the onset of an acute LBP episode (baseline), a two-month follow-up, and at four months for 25 LBP patients and a pain-free control group of 48 subjects.  LBP patients were recruited from a variety of treatment facilities, physicians, and practitioners. Excluding criteria included any history of serious spinal injury or back surgery, pregnancy, or any painful condition requiring at least a month of treatment in the past year or one that affected the subject’s ability to function in any way on a regular basis or required the use of long-term pain medications. Demographics including sex, age, race, work status, and body mass index (BMI) were collected from the LBP and pain-free control participants at the beginning of the study.

Collecting Initial and Follow-Up Data

Patients with LBP answered questions about their pain’s onset, duration, intensity, and how well they were able to function while in pain. The participants then answered questions about their levels of depression, anxiety, and scale of stress. Back pain patients also answered questions that would indicate how much they catastrophized their pain and how self-sufficient they were at dealing with their pain, as well as questions designed to measure the sensory and emotional or affective connection to their pain. They were screened by questionnaires to determine possible neuropathic features of their LBP. All participants involved in the study were given the questionnaires to complete at each of their three assessments, and they were then classified into blind groups according to their answers.

Sensory Testing

All patients were tested for their cold-pain threshold (CPT), followed by a test for their heat-pain threshold (HPT), mechanical wind-up ratio (WUR), pressure-pain threshold (PPT), two-point discrimination (TPD), and conditioned pain modulation (CPM). The testing was conducted at the same three body sites on the backs and hands of all patients. The LBP patients’ back testing was conducted at the location of their greatest pain. Thermal pain thresholds were measured using three consecutive measurements. Pain from the stimulus of a single pin-prick, followed by that of a 10-pin prick, was used to measure the WUR of all subjects and then compared using analysis of a numerical calculation. Three measurements of pressure-pain were used to calculate the PPT. A ruler was used to calculate the TPD of all subjects.

A series of 30-second contacts with a thermally-heated device was used to measure heat pain, and a cold foot bath was used to determine the subjects’ sensitivity to cold, as they were asked to withdraw their foot when they were no longer capable of tolerating the cold water. They were then asked to rate their discomfort at 30, 60, and 90 seconds on a pain scale, and their score was given a negative or positive inhibitory response value. Data and statistics were computed and analyzed by the researchers using statistical software.

Results

The data collected in this study showed that the chronic LBP group had a significantly increased pain sensitivity during early and later pressure and mechanical tests and were more cognizant of pain responses at baseline than their pain-free and recovered acute LPB study counterparts. The psychological effects of their pain were also measured higher at the two and four-month follow-up than their recovered LBP counterparts. This could mean that those patients were neurologically and/or psychologically more prone to pain, even prior to the development of their LBP symptoms. The study authors suggest better standardization of a CPM protocol in future studies to take psychological factors of the patients into account and improve the reliability of future test results.

 

KEYWORDS: correlation between persistent LBP and somatosensory changes, link between heightened pain sensitivity and its possible role in the development of chronic LBP. patients undergoing initial LBP diagnosis also be evaluated for potential psychological issues, cold-pain threshold, heat-pain threshold, conditioned pain modulation

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