Neuroendocrine Manifestations in Sjögren's Syndrome: Relation to the Neurobiology of Stress

Abstract

Evidence suggests that autoimmune rheumatic diseases are associated with neuroendocrine dysfunction. Sjögren's syndrome (SS) is proposed as an ideal model to study perturbations in the neuroimmune axis, since patients tend to be medication free and studies are not confounded by the effects of chronic immunosuppressive therapy. The functional integrity of the adrenal, gonadal, and thyroid axes was assessed in SS. Pituitary function of the HPA axis was evaluated directly by determining the ACTH released during oCRH stimulation, while adrenal function was assessed indirectly by endogenous ACTH released during oCRH stimulation. Low basal activity of the HPA axis was associated with pituitary hyporesponsiveness to exogenous CRH, as well as hyporesponsiveness of the adrenal glands to endogenous ACTH. These findings are compatible with a central deficiency of the adrenal axis. An overall attenuated and delayed LH and FSH response to LHRH stimulation was also indicative of central dysfunction of the gonadal axis in SS. SS patients demonstrated elevated basal TSH levels and evidence of mild hypothyroidism. Basal prolactin concentrations were also elevated in SS, and both TSH and PRL showed relatively increased responses to TRH stimulation. The data suggest a central deficiency in all three neuroendocrine axes: adrenal, gonadal, and thyroid. It is not clear if any one system plays a primary role in the expression of the disease. Rather, it is likely that the net effect involves the synergistic and antagonistic effects of multiple hormones. Taken together, adrenal and gondadal steroid hormone deficiency, plus elevated PRL levels, probably greatly affect immune function in SS patients.