Herpes folliculitis: clinical, histopathological, and molecular pathologic observations

Herpes folliculitis is a rare manifestation of herpes virus infection and it is often misdiagnosed. Diagnostic criteria are not well established, only 24 patients being reported in the literature. Recently it has been suggested that herpetic folliculitis is more common in infections with varicella zoster (VZV) than in those with herpes simplex viruses (HSV-1 and -2).

To refine diagnostic criteria for folliculitis caused by VZV, HSV-1 and HSV-2, and to study whether follicular involvement enables morphological differentiation between VZV and HSV infections.

Twenty-one patients with herpetic infection of follicular epithelium were assessed clinically and histopathologically. Polymerase chain reaction (PCR) studies for specific DNA of herpes viruses were performed on paraffin-embedded biopsy specimens.

In 17 of our cases PCR was positive for VZV, four were positive for HSV-1, none for HSV-2. The clinical presentation of herpes folliculitis often lacked vesicles or pustules (14/21). Histopathological features were often devoid of ballooning (12/21), multinucleated giant cells (12/21) and keratinocytes with steel grey nuclei (15/21). The most consistent findings were lymphocytic folliculitis and perifolliculitis (20/21) and necrotic keratinocytes in follicular epithelium (12/21). In zoster, but not in varicella eruption or HSV infections, follicular involvement was unaccompanied by marked changes in the epidermal surface.

In biopsy specimens taken from herpes virus infections, involvement of follicular units is more commonly encountered in VZV infections compared with HSV infections. Early in the course, herpes folliculitis presents as lymphocytic folliculitis devoid of epithelial changes considered to be diagnostic of herpes virus infections. Exclusive involvement of follicles is rather typical of zoster.