Fig. 7.

An imbalance between metalloproteinases (MMPs) and tissue-inhibitor of metalloproteinases (TIMP) is suspected in the pathogenesis of MDE. (1) In MDE lesional skin there is an increased number of CD68 + and CD34 + histiocytes. (2) There is also increased expression of MMP-1, MMP-9, and MMP-12 with decreased elastase inhibitor TIMP-1. (3) Ultraviolet B, infrared, and visible light are hypothesized to play a role in alteration of MMP expression. (4) Disruption of this balance is thought to lead to degradative processes such as increased elastolysis in MDE.