Herpes incognito most commonly is herpes zoster and its histopathologic pattern is distinctive!

Infections of the skin by herpesviruses do not always present themselves in typical fashion. Conventional microscopy is used routinely to confirm infection by herpesviruses, but sometimes typical signs such as multinucleated epithelial cells or "ghosts" of them are not encountered in a specimen (so-called herpes incognito). We studied 35 patients in whom infection with herpesviruses was differentially diagnosed clinically but in whom a biopsy specimen had been taken for confirmation. Only those patients in whom histopathologic findings had been interpreted as being "not diagnostic" of herpesvirus infection by 2 independent dermatopathologists were included. Clinical and histopathologic findings were correlated with results from polymerase chain reaction studies on formalin-fixed paraffin-embedded tissue. Polymerase chain reaction revealed herpesvirus-specific DNA in 12 of 35 specimens, 10 being varicella zoster virus (VZV) positive, 1 herpes simplex virus (HSV)-2 positive, and 1 HSV-1 positive. Ten of these 12 cases presented themselves in very similar fashion (8 VZV, 1 HSV-1, 1 HSV-2). All lesions were macular or papular and typified mostly by dense perivascular and sparse interstitial superficial and deep infiltrates of lymphocytes, sometimes assuming a patchy lichenoid pattern. Infiltrates were prominent in and around adnexal structures, often peppering follicles, sebaceous glands, and eccrine glands. Lymphocytes were also found in the lower part of the epidermis accompanied by a combination of spongiosis and vacuolar alteration. The papillary dermis was often edematous; extravasated erythrocytes in variable numbers were a common finding. Lymphocytes sometimes had large and polygonal nuclei. Neutrophils and nuclear dust were present occasionally; eosinophils were rare. We conclude that herpes incognito most commonly is herpes zoster and its histopathologic pattern is distinctive.