CONCISE COMMUNICATION Inefficacy of topical thyroid hormone analogue TriAc in plaque psoriasis: results of a double-blind placebo-controlled trial A.VAHLQUIST , H.TO ¨ RMA ¨ AND B.CARLSSON* Department of Medical Sciences (Dermatology), University Hospital, SE-751 85 Uppsala, Sweden *KaroBio AB, SE-141 04 Huddinge, Sweden Accepted for publication 17 January 2004 Summary Background Thyroid hormone receptors are expressed in human skin and are believed to be involved in the regulation of epidermal proliferation and differentiation, i.e. processes which are disturbed in psoriatic skin lesions. Ligands of the thyroid hormone receptors have so far not been tested as antipsoriatic agents. TriAc (3,3¢,5-triiodo-thyroacetic acid) is a well-known thyroid hormone analogue with much reduced cardiac thyrotoxic activity compared with the classical thyroid hormones. Objectives To determine the effectivness and side-effects of topical TriAc in patients with chronic plaque psoriasis. Methods Twelve patients with mild to moderate psoriasis were treated with TriAc (0Æ1% in hydrophilic ointment) and placebo applied twice daily to either of two (or several) bilaterally symmetrical plaques for 8 weeks. The patients and investigator were blinded as to the content of the tubes. Every 2 weeks the treated plaques were evaluated by the patient (using a balanced visual analogue scale for a right–left comparison) and by the investigator (using a psoriasis severity index and a global assessment of each plaque). Results After 8 weeks of treatment, more than 33% improvement of the psoriasis index occurred in 10 of 12 TriAc-treated and nine of 12 placebo-treated plaques. There were no statistically significant differences between the treatments in terms of reduction of the scores for erythema, scaling, induration or pruritus during the study. Half of the patients considered TriAc superior to placebo, whereas three of 12 were of the opposite opinion (P >0Æ05). The global assessment showed marked improvement or remission in six TriAc-treated and five placebo-treated cases (P >0Æ05 for difference). No adverse effects were noted. Conclusions TriAc in the dosage and formulation studied was safe but no more effective than placebo in treating plaque psoriasis. However, newer thyroid hormone analogues (agonists or antagonists) might be more active and should be further explored in this context. Key words: clinical trial, psoriasis, thyroid hormone, topical treatment Current treatments for psoriasis embrace hormonal compounds such as vitamin D (e.g. calcipotriol), retinoids (e.g. tazarotene) and glucocorticoids (e.g. betamethasone and clobetasol). All these compounds bind to nuclear transcription factors believed to be important for keratinocyte differentiation and prolifer- ation. Thyroid hormones bind to similar receptors, 1 but have never been tested before in psoriasis, even though thyroid hormone receptors are downregulated in pso- riatic skin. 2 TriAc (3,3¢,5-triiodo-thyroacetic acid) is a well- known thyroid hormone analogue with reduced car- diac thyrotoxic activity compared with thyroxine (T4) and triiodothyronine (T3), 3,4 but with an equal potency to T3 in noncardiac tissues. 5 TriAc was recently shown to prevent glucocorticoid-induced skin atrophy in mice. 6 The primary objective of this study Correspondence: Anders Vahlquist. E-mail: anders.vahlquist@medsci.uu.se British Journal of Dermatology 2004; 151: 489–491. DOI: 10.1111/j.1365-2133.2004.06037.x Ó 2004 British Association of Dermatologists 489