Study of Indoleamine 2,3-dioxygenase Activity, Serum Levels of Cytokines, BDNF, BH4 and Mirtazapine Efficacy in Fibromyalgia Syndrome

This study aims to investigate the anti-nociceptive biogenic amine (serotonin [5-hydroxytryptamine; 5-HT], norepinephrine [NE], dopamine [DA], and their metabolites) status, and serum levels of cytokines, BDNF and BH4 in Thai fibromyalgia syndrome (FMS) patients compared with a representative Thai population. The efficacy and the tolerability of mirtazapine as monotherapy for FMS will also be assessed. In addition, proof of concept of the indoleamine 2,3-dioxygenase (IDO) activity in FMS will be conducted.

The study will be divided into three parts. In part I, FMS patients of Thai ethnicity will be examined to determine the blood and/or urinary level of anti-nociceptive biogenic amines, cytokines, BDNF and BH4 by comparison with the demographically matched, but unrelated, healthy normal controls (HNC). In part II, the FMS subjects from part I study will be randomized to blinded therapy with mirtazapine or identical appearing placebo. There will be three treatment groups (N=1:1:1) to accommodate two dosages of mirtazapine (15 mg, 30mg) and placebo given before bedtime. Pill counts at baseline and at follow-up visits will document compliance. Standard outcome instruments (translated and validated in Thai language) will be used at baseline and at each of the follow-up visits. The co-primary outcome variable will be the changes in the pain visual analog scale (PVAS) score and pain responders (>= 30% PVAS reduction). Secondary clinical outcome variables of interest will include depression, insomnia, anxiety, physical function, morning stiffness, patient global assessment of disease status, patient global impression of change, fibromyalgia impact questionnaire (FIQ, quality of life and adverse experience. The changes of biogenic amine and IGF-1 concentrations in blood and/or urine with the treatment will be examined as the secondary biochemical measures. In part III, the IDO activity of depressed FMS, non-depressed FMS and HNC will be compared. Moreover, the effect of mirtazapine treatment on the IDO activity in depressed and non-depressed FMS patients will be assessed.

Study hypothesis

1. Anti-nociceptive biogenic amine levels in Thai FMS patients are lower than in Thai healthy normal control. 2. Higher IDO activity could be observed in FMS patients. 3. Higher cytokines could be observed in FMS patients. 4. Higher BDNF could be observed in FMS patients. 5. Lower BH4 could be observed in FMS patients. 6. Mirtazapine is effective in FMS treatment.