The classification of patients with chronic pain: age and sex differences.

OBJECTIVE: To further develop an empirically based classification system for chronic pain patients through the examination of age and sex differences, and incorporation of pain duration in the grouping algorithm. SUBJECTS: Three hundred seventy-four chronic pain patients (300 aged 13 to 59 years; 74 aged 60 to 89 years) assessed at an outpatient, multidisciplinary pain management centre. METHODS: Patients completed measures of demographic and descriptive information, pain intensity (box rating scale), perceived disability (modified Pain Disability Index) and affective distress (Symptom Checklist-90 Revised) before multidisciplinary treatment. Standardized scores from the assessment measures were entered into a series of hierarchical, multivariate cluster analyses to identify underlying patient subgroups. RESULTS: Age-based patient groupings from prior research were partially replicated. Significant differences in clinical presentations were observed across age and sex groups. Pain duration was found to make an important contribution to the patient groupings. 'Good control' (low pain, disability, distress) and variants of 'chronic pain syndrome' (elevated pain, disability, distress) groupings were identified across all analyses. Two variants of a 'stoic' profile were identified among older patients, with low levels of distress relative to pain and perceived disability. One of these profiles was associated with long pain duration and was found only among males. Several unique clinical profiles were identified for female patients. CONCLUSIONS: There are important age and sex differences in the clinical presentations of chronic pain patients. Some older patients present with unique clinical profiles that may reflect cohort differences, and/or physiological or psychological adjustment processes. There appears to be a greater number of distinct chronic pain presentations among females. Research on the classification of chronic pain patients within homogeneous diagnostic subgroups is needed.

Staircase assessment of the magnitude and time-course of 50% nitrous-oxide analgesia.

The analgesic effect of 50% nitrous oxide and oxygen on thermal pain sensations was evaluated in a placebo-controlled, double-blind crossover design. In a session immediately before oral surgery, 20 patients used a seven-point verbal scale to rate the intensity of pain sensations evoked by three-second thermal stimuli delivered to 14 sites on the volar forearm at 20-second intervals by a 1-cm-diameter contact thermode. Subjects rated 36 stimuli while breathing room air and then two additional sets of 36 stimuli while inhaling 50% nitrous oxide and oxygen during one set and oxygen placebo during the other. Each of these two stimulus sets was preceded by a two-minute induction of the agent, and the sets were separated by a three-minute washout period. Order of administration was randomized and counterbalanced. Stimulus temperatures were adjusted continuously by an interactive computer program so that response could be maintained at predetermined levels. This method resulted in a continuous measure of analgesia in units of stimulus intensity. Results showed that, in comparison with placebo, nitrous oxide significantly increased the stimulus temperatures (mean = 0.42 degrees C) required to make the same response [F (11,209) = 6.76, p less than 0.0001], indicating analgesia. This increase was one-third to one-half that observed with clinical doses of intravenous fentanyl. Analgesic effects were apparent at three min and wanted 10 min after termination of nitrous-oxide inhalation. These times closely correlated with previous measures of alveolar concentration, further supporting the fast but modest analgesic action of nitrous oxide.