Primary fibromyalgia syndrome (PFS) is a nonarticular rheumatological syndrome characterized by disturbances in the hypothalamo-pituitary-adrenal (HPA) axis. The site of the defect in the HPA axis is a matter of debate. Our aim was to evaluate the HPA axis by the insulin-tolerance test (ITT), standard dose (250 microg) ACTH test (SDT) and low dose (1 microg) ACTH test (LDT) in patients with PFS.
Sixteen patients (13 female, three male) with PFS were included in the study. Sixteen healthy subjects (12 female, four male) served as matched controls. ACTH stimulation tests were carried out by using 1 microg and 250 microg intravenous (i.v.) ACTH as a bolus injection after an overnight fast, and blood samples were drawn at 0, 30 and 60 min. The ITT was performed by using i.v. soluble insulin, and serum glucose and cortisol levels were measured before and after 30, 60, 90 and 120 min. The 1 microg and 250 microg ACTH stimulation tests and the ITT were performed consecutively.
Peak cortisol responses to both the low dose test (LDT) and standard dose test (SDT) (589 +/- 100 nmol/l; 777 +/- 119 nmol/l, respectively) were lower in the PFS group than in the control group (1001 +/- 370 nmol/l; 1205 +/- 386 nmol/l, respectively) (P < 0.0001). Peak cortisol responses to ITT (730 +/- 81 nmol/l) in the PFS group were lower than in the control group (1219 +/- 412 nmol/l) (P < 0.0001). Six of the 16 patients with PFS had peak cortisol responses to LDT lower than the lowest peak cortisol response of 555 nmol/l obtained in healthy subjects after LDT. There was a significant difference between the peak cortisol responses to LDT (589 +/- 100 nmol/l) and peak cortisol responses to ITT (730 +/- 81 nmol/l) in the PFS group (P < 0.0001). Peak cortisol responses to SDT (777 +/- 119 nmol/l) were similar to peak cortisol responses to ITT (730 +/- 81 nmol/l) in the PFS group.
We conclude that the perturbation of the HPA axis in PFS is characterized by underactivation of the HPA axis. Some patients with PFS may have subnormal adrenocortical function. LDT is more sensitive than SDT or ITT in the investigation of the HPA axis to determine the subnormal adrenocortical function in patients with PFS.