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pain relief were withdrawn from the study.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pain, patients with this diagnosis were withdrawn from the partial response group.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 trigger 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: 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) microg/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
low 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: