Is it common or have there been many clinical cases of KS flat lesions (non-nodule type), that blanch completely upon applying light pressure?

All the literature that I've had to read says that KS does not blanch upon pressure. However, it seems that this literature might only be referring to the nodule type lesions.

Secondly, what allows for blanching in a regular (trauma induced) lesion versus non-blanching in most KS lesions (of all types).

KS can come in so many varied forms and colors. The lesions are often in the shape of an ellipse. They can be pink, red, purple, and brown. They can range in size from tiny to many inches in diameter. They can be flat or nodular. So there is no "typical" lesion.

As for blanching, blanching is seen is any condition in which there are many blood vessels. When you apply pressure, lesions with blood vessels often turn white (i.e. blanch). Early KS lesions can indeed blanch, but as the KS lesions become more established, most do not blanch. I have personally never found the presence or absence of blanching useful when it comes to making a diagnosis. The only way to know if a lesion is KS or not, is to have either it or a similar lesion biopsied. One last point is that KS lesions on the feet can change in color and intensity after walking about. The pressure on the feet can alter blood flow to the KS lesions and this in turn can change how lesions look.

Hope this helps. BD.