While mast cells are normally present in the skin in small
numbers in a perivascular pattern, in mast cell diseases an
increased number of mast cells is present. In telangiectasia
macularis eruptiva perstans, the increase in mast cell numbers
is small. Their nuclei are typically spindle-shaped, and they
are concentrated around blood vessels. Often they resemble
fibroblasts, therefore special stains are needed to identify the
mast cells. Within the dermis, there is a perivascular and
interstitial infiltrate of mononuclear cells. Abundant cells
containing round, oval or spindled nuclei with ample cytoplasm
are present within this infiltrate. Their cytoplasm is
characterized by the presence of metachromatic granules,
highlighted upon staining with Giemsa, toluidine blue or Leder
stains.