Endocrine-mediated mechanisms of fatigue during treatment with interferon-alpha

Fatigue occurs in more than 70% of patients treated with interferon-alpha (IFN-alpha) and is the most problematic toxicity associated with IFN-based immunotherapy. Abundant evidence suggests that immune-mediated endocrine disease occurs during IFN-alpha therapy, which may contribute to the etiology of fatigue. Autoimmune thyroid disease is a well-recognized consequence of IFN-alpha therapy and may be mediated by the induction of IFN-gamma production by lymphocytes. Administration of exogenous IFN-gamma has been associated with upregulation of class II major histocompatibility antigens in the thyroid and the development of thyroiditis. Interferon-alpha also stimulates the production of interleukin-6; both interleukin-6 and IFN-gamma have specific effects on thyrocyte function. There also is evidence suggesting that IFN-alpha initiates a cytokine cascade that effects the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes, thus affecting regulation of glucocorticoid and sex steroid hormone secretion, but the clinical significance of these observations has not been established. Although endocrine disease will not explain the occurrence of fatigue symptoms in all patients, there is clear evidence that hormonal deficiency syndromes occur in a relatively large portion of patients receiving systemic IFN-alpha therapy. Most importantly, the possibility of hypothyroidism must be considered; however, diagnosis of hypothyroidism in cancer patients is complicated by the occurrence of the "sick euthyroid syndrome." Clinical recommendations for assessment and treatment of IFN-alpha-induced fatigue are offered. Most importantly, measurements of thyroid-stimulating hormone and antithyroid autoantibodies should be used to evaluate thyroid status. Acknowledging the limitations of current clinical data, adrenal- and gonadal-axis dysfunction also must be considered in patients with IFN-alpha-induced fatigue.