RESUMEN
What is known and objective Polymyxins were widely used until the 1960s; however, they fell into disfavour owing to their toxicity. The subsequent growth of infections caused by multidrug-resistant Gram-negative bacteria has led to renewed use of this class of antimicrobials in clinical practice. Acquired skin hyperpigmentation (SH) following intravenous polymyxin B treatment has been previously reported, but little is known about its pathogenesis, clinical course and treatment. To improve understanding of these issues, we conducted a prospective study of adult patients receiving intravenous polymyxin B treatment. Methods Patients receiving intravenous polymyxin B treatment were followed throughout the course of treatment. Clinical, dermatoscopic, histologic and immunohistochemical skin properties of patients who presented with SH were studied. Results and discussion Skin hyperpigmentation was noted in 8% of patients (n=20/249); however, clinical, dermatoscopic, histologic and immunohistochemical examinations were performed only in three patients for whom the consent of relatives was obtained. Histologic and immunohistochemical findings showed an abundant melanocyte-pigmented dendritic network. Langerhans cells' hyperplasia and dermal IL-6 overexpression were also found, presumably for an inflammatory process due to polymyxin B use. As polymyxin B causes the release of histamine, which is known for its melanogenic effect, it is possible that skin darkening is associated with this inflammatory mediator. What is new These clinical and dermatoscopic findings contribute to a better understanding of how the pigmentary reaction manifests following intravenous polymyxin B treatment. Conclusion We concluded that hyperpigmentation due to intravenous polymyxin B treatment is associated with an inflammatory process and subsequent melanocyte activation. Although the pigmentary disorder neither influences the outcome of the therapy nor warrants discontinuation of treatment, it nevertheless considerably affects the patient's quality of life.