- Caused by viral reactivation in patients previously infected by varicella zoster virus (VZV)
- Painful vesicles on an erythematous base in the distribution of a sensory dermatome
- Most often seen in elderly and immunocompromised individuals
- Immunocompromised patients are at risk for disseminated infection.
- The changes are identical to those seen in varicella and herpes simplex:
- "Steel gray" keratinocyte nuclei
- Multinucleated keratinocytes with margination of chromatin ("pomegranates")
- Eosinophilic nuclear inclusions surrounded by clear haloes
- Intracellular edema and ballooning degeneration
- Intraepidermal vesiculation
- Dense dermal lymphocytic inflammation
- Sometimes inflammation of nerve twigs and/or vasculitis is seen.
- Immunocompromised patients may have marked necrosis of the epidermis and widespread involvement of adnexal structures.
Herpes zoster folliculitis:
- Herpes simplex and herpes zoster virus do not typically involve the hair follicles, but may occasionally do so, particularly in early infection.
- Lesions may be especially widespread and severe in immunocompromised patients.
- Viral cytopathic effects may be seen within the hair follicles: dysmaturation, acantholysis, dyskeratosis, multinucleate keratinocytes.
- There may be focal to extensive necrosis of the hair follicle.
- The dermis shows dense perivascular and sometimes perineural lymphocytic infiltrates, in some cases with atypia that may mimic lymphoma.