Indeed, there seems to be a clinical overlap between CFS and Addison disease. However, a direct link between the endocrinological disturbances and the reduced exercise capacity has yet to be proved.
Unlike in Addison disease, in which hypocortisolemia is related to an autoimmune phenomenon, in CFS low cortisol levels could be attributable to altered intracellular mechanisms, eg, a decreased signal transduction to the receptors in the target organ.1 This could lead to decreased intracellular messenger RNA as a consequence of dysfunction of the 2-5A synthetase/ribonuclease L pathway in CFS exerting a negative control on protein synthesis.2,3 Both the novel low-molecular-weight ribonuclease L2,3 and interaction of the ribonuclease L ankyrin domain with ABC transporters4 could play a role in this mechanism.
De Becker P, De Meirleir K. Chronic Fatigue Syndrome, Decreased Exercise Capacity, and Adrenal Insufficiency—Reply. Arch Intern Med. 2001;161(12):1558-1559. doi: