Clinical history: 38 year old male with a vesicular eruption on his right shoulder
What is the most probable diagnosis?
Herpes simplex virus is a DNA virus with two subtypes (HSV-1 and HSV-2). The majority of infected patients do not develop lesions but when a cutaneous eruption is present, HSV-1 tends to cause mostly oral lesions and HSV-2 mostly genital and anal lesions. Patients with atopic dermatitis may develop widespread lesions (eczema herpeticum).
Clinically, the typical appearance is of clustered vesicles on an erythematous base and the presentation tends to be recurrent and painful. Triggers include UV light, stress and depressed immunity.
Histologically, there is ballooning change of the epidermis and acantholysis. Early lesions may demonstrate reticular degeneration, epidermal necrosis and intraepidermal vesicles. Evidence of viral infection is demonstrated by multinucleated cells with ground-glass nuclear inclusions, nuclear moulding and margination of chromatin. Within the dermis there is a lymphohistiocytic infiltrate.
The main differential diagnosis is varicella-zoster virus (VZV) which cannot be distinguished histologically from herpes simplex.
Herpes simplex cutaneous infection is generally a self-limited disease however infection is lifelong due to persistence of the virus in the dorsal root ganglion. The condition is treated by antivirals (acyclovir, valacyclovir etc).