Posted in Web PSD | definition of PSD by Medical dictionary July 10, 2019 PSD classically presents as a well-demarcated perianal erythema with or without exudate, which may centrifugally spread to the penis or vulva and is present in more than 90% of patients with PSD (1, 2, 17-19). : https://medical-dictionary.thefreedictionary.com/PSD