Thyroid autoimmunity and hypothyroidism during long-term treatment with recombinant interferon-alpha.

Forty-five patients with myeloproliferative or myelodysplastic syndromes, treated with recombinant interferon-alpha (rIFN-alpha) for a minimum of 1 up to 4 years, were examined for the occurrence of thyroid autoimmunity. During treatment, the rate of thyroid autoimmunity rose to more than 20%. The decrease in severity and frequency of thyroid autoimmunity after withdrawal of IFN shows that this is a potentially reversible side effect. The key determinant for the manifestation of this IFN-related autoimmune phenomenon seems to be a predisposition for autoimmunity, since patients with initially detectable thyroid antibodies are prone to exacerbations of thyroid autoimmunity. Concurrent with thyroid autoimmunity, hypothyroidism occurred but did not correlate with the levels of thyroid antibodies, although severe hypothyroidism in two patients was accompanied by increased levels of thyroid antibodies. This investigation shows that thyroid autoimmunity and consecutively hypothyroidism must be expected in certain patients treated with rIFN-alpha during long periods. Furthermore, it may be assumed that IFN-alpha does not induce the development of autoimmunity, but rather enhances the levels of pre-existent thyroid antibodies.