The impact of comorbidities in fibromyalgia (FM) and temporomandibular disorders (TMD) have been well documented, but whether TMD sub-diagnoses myalgia (MYA) and myofascial pain with referral (MFP) differ regarding comorbidity is unclear. We aimed to elucidate this by studying the presence and associations of comorbidities in FM, MFP and MYA. An extended version of the Diagnostic Criteria for TMD axis II questionnaire was used to examine demographics, pain and comorbidities in 81 patients with FM, 80 with MYA, and 81 with MFP. Patients with MFP and FM reported a higher percentage of irritable bowel syndrome (IBS), depression, anxiety, somatic symptoms, perceived stress, and insomnia compared to MYA. Patients with FM had more IBS, depression, and somatic symptom disorder versus MFP. After adjusting for confounding variables, participants with anxiety, somatic symptoms disorder, pain catastrophizing, and perceived stress, as well as a greater number of comorbidities, were more likely to have MFP than MYA, whereas FM participants were more associated with IBS, somatic symptoms and insomnia compared to MFP. The number of comorbidities was significantly associated with widespread pain but not pain duration, body mass index or being on sick leave. In conclusion, patients with MFP were more similar to those with FM regarding comorbidity and should be differentiated from MYA in clinical settings and pain management.

Background: Both temporomandibular disorders myalgia (TMDM) and fibromyalgia (FM) have been linked to central and peripheral changes in serotonin availability. The precursor of serotonin, tryptophan (TRP), is mainly catabolised via another pathway to produce kynurenine (KYN), but whether changes of this pathway are present in TMDM and FM are still unclear. Objective: The aim was to explore blood plasma concentrations of TRP and KYN in TMDM and FM in an attempt to identify novel associations for future research. Methods: Plasma of 113 female participants (17 TMDM, 40 FM and 56 healthy painfree controls) were analysed for TRP and KYN concentrations. The degradation of TRP via the KYN pathway was indicated by the KYN to TRP ratio (KYN/TRP). Pain intensities were assessed with the Graded Chronic Pain Scale (GCPS) and Visual Analogue Scale (VAS). Psychological symptoms were evaluated using the Hospital Anxiety and Depression Scale (HADS), Patient Health Questionnaire (PHQ-9) and General Anxiety Disorder scale (GAD-7). Results: In TMDM there was a negative correlation between TRP and pain intensity (r s = −0.55 P = .023) and positive correlations between KYN/TRP and pain intensity (r s = 0.59 P = .013). In FM, KYN/TRP was negatively correlated with anxiety symptoms (r s = −0.36 P = .022) and a trend towards significantly lower TRP levels was found compared to controls (P = .05). Conclusion: The association between KYN/TRP and pain intensity as well as anxiety ratings in this small exploratory study may indicate that KYN/TRP could be a relevant indicator for symptom severity in TMDM and FM. Further investigations of the KYN pathway in chronic myalgia are warranted. K E Y W O R D S fibromyalgia, temporomandibular disorders, kynurenine pathway, pain, psychological symptoms, tryptophan metabolism | 151 BARJANDI et Al. How to cite this article: Barjandi G, Louca Jounger S, Löfgren M, Bileviciute-Ljungar I, Kosek E, Ernberg M. Plasma tryptophan and kynurenine in females with temporomandibular disorders and fibromyalgia-An exploratory pilot study . J Oral Rehabil. 2020;47:150-157.