While it is uncommon in those of Asian ancestry, this patient has psoriasis. (The involvement of her scalp and arms helps to corroborate this diagnosis.) But she has other issues that serve to confuse the picture: Her extreme obesity and pendulous breasts trap heat and sweat, which induces a condition called intertrigo. This chronic inflammatory process has become “koebnerized,” a phenomenon in which psoriasis appears in a traumatized area, such as a surgical wound or burn. To make matters even worse, the skin immediately under her breasts has darkened as a result of postinflammatory hyperpigmentation.
So this patient actually has three overlapping problems: intertrigo, koebnerized psoriasis, and postinflammatory hyperpigmentation. Her obesity, which is unlikely to improve, is a major contributor to each. Luckily, the inframammary skin changes are relatively asymptomatic.
All three problems can be alleviated by reducing heat and sweat (with antiperspirants, talcum-based powder, weight loss, and use of cotton cloth to separate the breasts from the underlying chest skin), and through use of topical class III steroid creams. We can stop treating it as a yeast infection, because yeast plays little to no part in the process.
TAKE-HOME LEARNING POINTS
• Skin injury—whether from surgery, burn, excoriation, or chronic maceration—can cause psoriasis to flare, a process known as the Koebner phenomenon.
• Intertrigo refers to an inflammatory condition affecting intertriginous areas such as the groin, axilla, abdominal or other folds, and inframammary skin.
• Intertrigo is caused by chronic maceration related to heat and perspiration and is especially common under the breasts.
• The same chronic inflammation that causes intertrigo and the Koebner phenomenon can also result in postinflammatory hyperpigmentation in those with darker skin.
• Bacteria and yeast organisms play only a small role, if any, in these processes.