Prurigo pigmentosa: a clinicopathological study and analysis of associated factors

Prurigo pigmentosa (PP), a rare inflammatory disease of the skin, is mostly reported in the ethnic Japanese population. Its pathogenesis remains unclear. The chronic and recurrent nature of PP implies a possible role of viral infection in the pathogenesis. The anti-inflammatory mechanism of doxycycline, which is well documented as a good treatment for PP, is related to the suppression of interleukin expression.

We identified and retrospectively analyzed 16 biopsy-proven and criteria-matched patients over a seven year period at a single medical center. DNA extracted from formalin-fixed, paraffin-embedded specimens was analyzed for herpes simplex virus-1 (HSV-1), HSV-2, and human herpes virus-6 (HHV-6) DNA by polymerase chain reaction. Immunohistochemistry was performed to determine the interleukin-6 (IL-6) and interleukin-8 (IL-8) expression in PP skin lesions.

Clinicopathological findings in the ethnic Chinese population are similar to those reported in Japanese studies. All patients had a good response to doxycycline treatment, with a mean duration of use of 2.4 weeks. However, recurrence was noted in six patients. HSV-1, HSV-2, and HHV-6 DNA in PP skin lesions were negative. Immunohistochemistry showed IL-6 (P = 0.035) to be more strongly expressed in PP skin lesions. There was no statistical significance of elevated IL-8 expression in PP (P = 0.123).

Prurigo pigmentosa is not uncommon in the ethnic Chinese population. There was no evidence of herpes virus DNA in PP skin lesions. Increased expression of IL-6 in PP skin lesions may explain the effects of doxycycline in terms of its anti-inflammatory properties.