Gold sodium thiomalate (GTM) induces hypersensitivity to thiomalate, the thiol carrier of GTM.

A case of the gold sodium thiomalate (GTM)-induced eruptions with thiomalate (TM) hypersensitivity was reported. A 61-year-old Japanese woman developed lichenoid and seborrheic dermatitis (SD)-like eruptions with alopetia, when the total dosage of GTM administered for rheumatoid arthritis became 110 mg. The eruptions slowly disappeared with pigmentation after discontinuance of the GTM therapy, and the resumption resulted in the development of similar eruptions. She showed a positive reaction to GTM in an intradermal test. She also showed a positive response to TM, which is the thiol carrier of GTM, in the patch test, but a negative one to metallic gold. After administration of auranofin (AF), she also developed the SD-like eruptions with hypersensitivity to metallic gold as well as AF on patch testing, but did not develop the lichenoid ones. Our animal experiments revealed an almost complete cross reaction between GTM and TM, but only a partial one between GTM and aurothioglucose, which have dissmilar structures in the carrier part for gold. Probable roles of hypersensitivity to TM and metallic gold, which are metabolites of GTM, were discussed, respectively, in the genesis of the GTM-induced lichenoid eruptions and the AF-induced SD-like eruptions.