Familial thioamide-induced lupus syndrome in thyrotoxicosis.

We describe 2 relatives both with thyrotoxicosis who developed a lupus-like syndrome after treatment with thioamide derivatives, methimazole (father) and propylthiouracil (son). The lupus syndrome consisted of joint pains, skin rash, and positive antinuclear antibodies (son), all of which resolved after discontinuation of the antithyroid medications. Both patients were identical at the HLA-DR locus suggesting adverse reactions to thioamides may be controlled by immune response genes. The clinician should be cautious about treating other family members when 1 member has had a drug-induced lupus syndrome. This is especially true if the disease in question is a known familial illness such as thyrotoxicosis.