Viral diseases can manifest as nonspecific exanthems, such as in measles and many other morbilliform eruptions, or more specific patterned eruptions, such as the papules on the cheeks, elbows, knees, and buttocks seen in Gianotti-Crosti syndrome. Primary lesions of viral infections vary from the vesicles seen in many herpetic and enteroviral conditions to the petechiae seen in the papular-purpuric gloves-and-socks syndrome due to parvovirus B19.
Skin lesion distribution is helpful when distinguishing between common vesicular eruptions, including the grouped localized vesicles and erosions seen in herpes simplex virus, compared with the dermatomal vesicular eruptions secondary to herpes zoster virus. As with other infections, the patient’s underlying immune status also plays a role in the clinical findings, as evidenced by the verrucous herpetic lesions or severe disseminated herpes zoster seen in immunocompromised patients. Other underlying conditions, such as concurrent eczema, can also contribute to the patterns of involvement as seen in eczema herpeticum and the newly coined eczema coxsackium due to Coxsackie virus A6. Obtaining viral cultures and polymerase chain reaction specimens from these lesions is a common way to establish the exact cause of many vesicular viral eruptions.
The age of the patient can particularly affect the cutaneous manifestations of viral illnesses, including the extramedullary hematopoiesis presenting as purple nodules in congenital cytomegalovirus infections (“blueberry muffin baby”) or the classic “slapped cheek” appearance due to erythema infectiosum (parvovirus B19) seen most commonly in school-aged children.
Uncommon viral infections are included, such as the zoonotic poxviruses like Orf that cause self-limited papulonodules, as well as even more exotic arthropod-borne viral infections such as Dengue and Chikungunya virus. Common viral conditions are included here as well, such as the dome-shaped, umbilicated, shiny papules of molluscum contagiosum and verruca vulgaris in its many forms secondary to human papillomavirus.
Finally, amid the many viral illnesses included in this portion of the atlas, human immunodeficiency virus deserves particular mention because it can cause a polymorphous primary eruption in the skin and is also associated with many other coinfections such as human herpesvirus 8 in the form of Kaposi sarcoma.