Postinflammatory hyperpigmentation secondary to external insult: an overview of the quantitative analysis of pigmentation.

CONTEXT: Despite new technologies, few studies have quantified changes in melanocyte numbers associated with postinflammatory hyperpigmentation (PIH) secondary to exogenous causes.

OBJECTIVE

This article aims to review what is known about the pathogenesis of PIH secondary to external insults and its relationship to the resultant degree of quantitative changes in melanocytes.

METHODS

We performed a review of articles exploring PIH resulting from external cutaneous insults retrieved through database searching. We reviewed relevant articles for the pathogenesis, histopathology, and quantitative changes in melanocytes related to specific etiologies of PIH. Methodologies to quantify pigmentation changes in dermatologic conditions with clinical hyperpigmentation were also explored.

RESULTS

Significant increases in melanocyte counts of irritant affected skin is seen compared with melanocyte counts of unaffected skin. An increase in melanocyte counts was also found for spontaneous inflammatory dermatoses, even in the absence of clinical hyperpigmentation. Furthermore, changes in melanocyte density and appearance are also seen secondary to inflammation. In addition, increases in epidermal melanocytes are seen with cutaneous exposure to certain agents, and melanocyte increases vary by exposure agent.

CONCLUSIONS

The degree of hyperpigmentation related to the intensity and duration of exposure to the causative factors of PIH is essential to better understand the pathophysiology of the disease process. The application of new methodologies to determine quantitative changes in melanocytes elicited by specific causative inflammatory agents has implications to prevent PIH, add to knowledge about disease duration, to develop better treatments for PIH, and to aid our understanding of the biology of the melanocyte.