Iatrogenic Kaposi sarcoma (KS) has previously been reported in patients with bullous pemphigoid (BP), in relation to systemic steroids. To report three cases of previously unreported cutaneous KS during treatment with superpotent topical steroids (STS) and methotrexate (MTX). All patients were elderly men with BP treated with STS for 2 to 32 months (cumulative doses: 2,700-9,150 g) before MTX was introduced (dosage: 10-12.5 mg/week). KS occurred one to nine months after the combined therapy. In one case, KS rapidly resolved after withdrawal of MTX. In two cases, vinblastine and/or radiotherapy were required to achieve regression of KS. Human herpes virus 8 (HHV8) latency-associated nuclear antigen was not expressed in BP lesions biopsied prior to development of KS (n = 3), but HHV8 DNA was detected in BP lesions from the patient with the most aggressive KS. Several predisposing factors were identified, including sex and age, high cumulative doses of STS, combination with MTX, and impaired immune status. In such cases, serum antibodies against HHV8 infection may be investigated in BP patients before introduction of MTX in order to guide clinical monitoring.
Keywords: Kaposi sarcoma; bullous pemphigoid; human herpes virus 8; methotrexate; topical steroids.