Temporomandibular joint pain, hyperalgesia and allodynia in relation to interleukin-1ß and serotonin

Abstract

This thesis had two main aims and comprises a methodological and a clinical part. The aims were to develop a temporomandibular joint (TMJ) synovial fluid (SF) sampling method that enables the determination of the true SF level of various substances and, by using the developed TMJ SF sampling method, investigate the hypothesis that circulating as well as SF content of interleukin-1ß (IL-1ß) and serotonin (5-HT) influence different TMJ pain entities and signs of tissue destruction in patients with TMJ inflammatory disorders.

In the methodological part of this thesis hydroxocobalamin (HCA; vitamin B12) was used as external marker. HCA mixed with saline is a dark red solution that was used in order to determine the dilution of the washing solution by SF. The difference in light absorbance of the aspirate and the washing solution was used as a measure of the dilution. This method was optimized for use with a spectrophotometric capillary tube system and the optimal wavelength, reproducibility and accuracy were determined. In addition, interaction between HCA and the analysis of various proinflammatory substances were investigated.

Patients with TMJ inflammatory disorders (local synovitis/capsulitis or polyarthritis) as well as healthy individuals were clinically examined concerning spontaneous TMJ pain, TMJ palpatory tenderness, pressure pain threshold and tolerance level, number of painful mandibular movements, mandibular mobility and degree of anterior open bite. TMJ SF samples were obtained and the SF samples as well as the plasma serum samples were analyzed with respect to concentration of IL-1ß and 5-HT.

The methodological part showed that the investigated vitamin B12-method was useful for determination of the washing solution dilution by SF. This information provides an estimate of the recovery of SF that can be used to determine the absolute SF concentration of a certain substance. The method was found to be precise as well as accurate and very small sample volumes were sufficient, which is an advantage in clinical studies of TMJ SF. The vitamin B12-method is reliable for measurement of SF concentrations of substances such as IL-1ß and 5-HT. With the most useful set of sample quality criteria applied, there was a recovery of TMJ SF of approximately 0.1 - 0.2 g. IL-1ß and 5-HT seem to be undetectable in TMJ synovial fluid from healthy individuals. The higher SF levels in the diseased TMJ (polyarthritis) compared to the healthy joint and with respect to IL-1ß and 5-HT is of clinical diagnostic relevance. Presence of IL-1ß and 5-HT in TMJ SF thus seems to indicate a pathological joint condition of inflammatory nature.

IL-1ß in the TMJ SF was found to be associated with spontaneous pain, hyperalgesia and allodynia in the TMJ region of patients with TMJ inflammatory disorders. IL-1ß was also a factor involved in the development of anterior open bite and the presence of IL-1ß in the TMJ SF seems to be a warning signal for TMJ tissue destruction. 5-HT in the SF was associated with pain perceived upon movement of the joint (allodynia) and to decreased mandibular mobility. The serum concentration of 5-HT was positively related to TMJ allodynia in patients with seropositive rheumatoid arthritis.