Pain intensity, illness duration, and protein catabolism in temporomandibular disorder patients with chronic muscle pain

To investigate whether the duration of chronic pain in temporomandibular disorder (TMD) patients is associated with a net depletion of amino acids, and a distinct process from pain intensity. Twenty-nine patients defined by the research diagnostic criteria/TMD as having Type 1a muscle pain (TMD1A group), and 34 age- and sex-matched control subjects, were assessed for variation in urinary organic and amino acid excretion by gas chromatography-mass spectrometry. The TMD1A patients' mean pain intensity, assessed on a visual analog scale (VAS), was 5.4 (95% confidence limits: 4.5 to 6.3), TMD1A illness duration was 5.0 +/- 1.2 (SD) years, number of body areas with pain/subject was 6.3 +/- 2.4 (range 0 to 10), and symptom prevalence from the Symptom Check List-90-Revised (SCL-90-R) was 25.5 +/- 11.3 symptoms/subject, which was higher than the controls (5.2 +/- 5.0 symptoms/subject, P < .001). TMD1A patient illness duration was positively correlated with symptom prevalence and body pain distribution, and all were independent of pain intensity. The TMD1A patients had: (1) and increased tyrosine:leucine ratio; and (2) reduced leucine concentrations (both P < .001), which suggests deregulated catabolism. Pain intensity was associated with: (1) changes in the multivariate urinary metabolite excretion patterns (P < .001); (2) reduced leucine concentrations (P < .001); and (3) increases in total urinary metabolites (P < .04), and in 2 unidentified molecules, UM28 (P < .001) and CFSUM1 (P < .002). TMD1A illness duration was associated with lower (1) urinary metabolite concentrations and (2) succinic acid and combined glutamine + glutamic acid levels, suggesting a progressive depletion of metabolite reserves. In TMD1A patients, total amino acid excretion was positively correlated with pain intensity and negatively correlated with illness duration, which indicated that illness duration was associated with a different set of metabolic anomalies compared with those identified for pain intensity.