Factors associated with failure of trigger point injections.

OBJECTIVE: The purpose of this study was to investigate factors that may influence the outcome of trigger point injections for myofascial pain syndrome. No prior studies have correlated preexisting factors with treatment outcome or assessed the magnitude of risk of treatment failure associated with such factors. DESIGN AND PATIENTS: Thirty-one factors derived from patient evaluation and physical examination were selected according to prior studies of mixed pain groups focusing on clinical importance and ease of assessment in a typical clinic setting. Included in the analysis were 193 patients who received trigger point injections and who completed baseline questionnaires. Factors were analyzed via univariate and logistic regression analyses both for independent association with short-term treatment outcome and for magnitude of risk of failure associated with each factor following adjustment for other factors. RESULTS: In univariate analysis an increased risk of treatment failure was associated with unemployment due to pain at the start of treatment, no relief from analgesic medication, constant pain, high levels of pain-at-its-worst and pain-at-its least, prolonged duration of pain, change in social activity, and lower levels of coping ability. Alcohol use was associated with a decreased risk of treatment failure. In logistic regression analysis, only lack of employment, prolonged duration, and change in social activity were independently associated with treatment outcome. Constant-versus-intermittent pain was included in the logistic model because there was an increase in risk that may be clinically important and because it influenced the effect of change in social activity. These results were not affected by the number or type of additional treatments the patients had. CONCLUSIONS: These results suggest that several factors should be considered in treating myofascial pain patients with trigger point injections, and this study supports the belief that pain is a multidimensional problem and that a variety of factors may influence treatment outcome.

1992 Bonica Lecture. Advances in chronic pain management since gate control.

OBJECTIVE: Two pain treatment systems that developed soon after the publication of the gate theory are probably a direct result of its publication: neuraxial opiate administration and electrical stimulation of the spinal cord and peripheral nerves and receptors. Although the use of these modalities has become widespread in managing chronic pain, there is disagreement about their long-term efficacy. This presentation will attempt to review the data regarding the mechanisms of action of these modalities and their efficacy in treating chronic pain of malignant and nonmalignant origin. DATA SOURCES: Data were derived almost entirely from original articles reporting experimental data from both animal and human studies and from series of patients undergoing treatment with the modalities reviewed. STUDY SELECTION: Where possible, controlled studies were selected. However, much of the available data regarding treatment results are uncontrolled. DATA EXTRACTION AND SYNTHESIS: Selected data from studies that were felt to be reasonably well conducted are presented or summarized. Because of the lack of control groups in many of the clinical trials, meta-analyses were not carried out. CONCLUSIONS: Long-term spinal opiate administration has been shown to be more effective than systemic opiates in some patients with cancer pain, but often must be combined with local anesthetics to provide satisfactory pain relief. Loss of effect over time is a significant problem. Since the identification of spinal opiate receptors and the introduction of spinally administered narcotics, a number of other receptors that are important in both sensitization and suppression of pain projection systems have been characterized. Agonists and antagonists to many of these receptors are being developed, and a few are available for clinical trials. Long-term electrical stimulation of the spinal cord produces substantial analgesia below the stimulated spinal segments in some patients with chronic pain. Although initial results are usually encouraging, long-term efficacy may be disappointing. It is postulated that analgesia associated with spinal stimulation is associated with both stimulation of large fiber ascending tracts and blockade of spinothalamic pathways. Transcutaneous electrical nerve stimulation (TENS) has come into widespread use in managing chronic pain and has had limited trials in cancer pain patients. It is well accepted by patients and physicians, but clinical studies of long-term efficacy have yielded variable results. The analgesic action is probably the result of both large afferent fiber activation and blockade of peripheral nociceptors.

Chronic pain therapy with transcutaneous electrical nerve stimulation: predictive value of questionnaires.

A retrospective study of 200 chronic pain patients was conducted to determine whether preexisting physical or social factors influence treatment success with transcutaneous electrical nerve stimulation (TENS). Responses to 30 questions from a preadmission questionnaire were analyzed against short-term treatment success. Patients with pain of more than a year's duration, who had undergone multiple surgical operations for pain control, who used tranquilizers, or who were not working because of pain, demonstrated a generally lower rate of treatment success, although the differences were not statistically significant. Treatment success rate was significantly higher for retired patients than for those with blue-collar jobs or those who were unemployed. There was no association between treatment success rate and site, frequency, character or severity of pain, age, sex, use of narcotic analgesics, or the presence of financial compensation or litigation. The value of TENS for chronic pain remains largely empirical.

Failure of naloxone to reverse analgesia from transcutaneous electrical stimulation in patients with chronic pain.

To investigate the possible role of endogenous opiates in the mediation of analgesia produced by low intensity, high frequency transcutaneous electrical stimulation in the presence of chronic pain, an attempt was made to reverse stimulation-induced analgesia with naloxone. Fifteen patients with chronic pain who were consistently relieved of pain by low intensity, high frequency transcutaneous stimulation were studied. During stimulation at 58 Hz, patients were given double-blind intravenous injections of either naloxone (0.4 or 1.2 mg) or saline. Subjective pain ratings were recorded before stimulation, after stimulation, and after naloxone and saline injections. No reversal of analgesia was seen after naloxone or saline. These results suggest that transcutaneous stimulation at low intensity and high frequency may provide analgesia that is not associated with release of endogenous opiates in patients with chronic pain.

Increased skin temperature during transcutaneous electrical stimulation.

Conflicting reports have appeared in the literature concerning the effects of transcutaneous electrical nerve stimulation on skin temperature. This report studied 33 patients with chronic pain involving one extremity (13 upper, 20 lower) to determine whether changes in sympathetic tone, as reflected in skin temperature, occurred in response to electrical stimulation of painful areas. Stimulation was carried out for 20 to 45 minutes. Skin temperatures were measured from the thumbs or great toes of stimulated and contralateral extremities before and during stimulation. Skin temperature rose 2.5 +/- 0.7 (mean +/- SEM) in both the ipsilateral and contralateral extremity in patients who experienced relief of pain during stimulation. There was no significant change in skin temperature in patients who experienced no relief.