The Oregon Health and Science University institutional review board approved all aspects of this study, and informed consent was obtained from each participant. Patients were diagnosed as having HHD if they demonstrated well-demarcated, symmetric, fissure-prone, painful, indurated, and hyperkeratotic plaques on the palms with a sharp cutoff at the wrist. In addition, there could be no personal or family history of typical chronic plaque psoriasis lesions elsewhere on the body, no history of atopic dermatitis, and no relevant positive findings on patch testing. Patients were considered to have palmoplantar psoriasis if they presented with well-demarcated, symmetric, indurated, and hyperkeratotic plaques on the palms with a sharp cutoff at the wrist. Patients were considered to have typical chronic plaque psoriasis if lesions were distributed on the extensor elbows, knees, scalp, nails, or trunk. All patients had chronic disease present for at least 6 months and all had not had topical therapy for at least 2 weeks and systemic therapy for at least 4 weeks.