Objective. A number of case reports and nonplacebo controlled studies have documented the efficacy of clonazepam (Klonopin) in the treatment of a number of chronic pain syndromes including lancinating and neuropathic/deafferentation pain. There are, however, no data on the efficacy of clonazepam for chronic pain (CP) associated with myofascial pain syndrome (MFPS). Therefore, we wish to report the results of an open clinical treatment trial of clonazepam for CP-associated with MFPS. Design. Forty-six patients with chronic pain (PWCP) and a diagnosis of MFPS were recruited into a clonazepam pain treatment open clinical trial. At entrance and completion of the study the patients completed a 10-cm visual analog scale (VAS) requesting them to rate their pain over the last 24 hours. Clonazepam was titrated upwards from 0.5 mg per day, at 0.5 mg increments, every 2 days. These patients rated their perceived pain relief daily on a 3-point rating scale: none, partial, total. Once a patient claimed partial pain relief clonazepam increases were stopped. Patients who complained of intolerable side effects before partial pain relief were withdrawn from the study. For a subgroup of patients claiming partial pain relief, clonazepam serum levels were determined. Because of the reported efficacy of clonazepam for neuropathic/deafferentation type of pain, patients with this diagnosis were withdrawn from the partial response group. Statistical analyses were performed on this remaining patient group with myofascial pain syndrome without a secondary diagnosis of neuropathic/deafferentation pain and partially responsive to clonazepam. Descriptive statistics were calculated for this group. Drop in pain level from entrance to partial response was tested for statistical significance via t test. In addition, 17 independent variables such as presence of nigger points, presence of burning pain etc, were utilized in a regression analysis, with drop in pain level as the dependent variable. A Pearson correlation analysis was first: performed in order to determine which of the independent variables significantly correlated with decrease in pain level. Independent variables having a Pearson r of .3687 or greater were selected for the regression procedure. Setting. Multidisciplinary pain facility. Patients. Patients with chronic pain with a diagnosis of MFPS and without neuropathic/deafferentation pain. Results. Of the 46 patients entered into the study, 9 were not titrated to partial pain relief because of intolerable sedation and 9 had a diagnosis of neuropathic/deafferentation pain. For the remaining group (n = 28), mean drop in VAS pain level from beginning of the study to partial response was 2.78 (SD = 1.94). This was statistically significant (t: = 5.49, P <.001). Mean clonazepam dosage to reach partial response was 2.41 (SD = 1.62) mg/day and the mean dosage per kilogram body weight per day was 0.04(SD = 0.03) mg. Mean clonazepam serum level was 30.58 (SD = 24.53) <mu>g/L. Decrease in pain level was associated with the presence of the following independent variables: trigger points (r =.451); range of motion restriction (r =.653); non anatomical sensory abnormalities (r =.370); chronic law back pain (r =.451); and burning pain (r =.482). In the regression analysis, restricted range of motion and presence of burning pain accounted for 42 % and 16% of the variance respectfully. Conclusion. Clonazepam may have an antinociceptive effect for pain associated with myofascial pain syndrome.
