On physical examination, the patient had multiple 
hyperpigmented plaques over the trunk, chest, abdomen, and back.

Rubbing the lesions produced a hive-like wheal.
(Positive Darier's sign).

There was an intact fluid filled vesicle on the anterior chest.  

The biopsy was done to confirm a clinical diagnosis of
urticaria pigmentosa.

The Leder stain is a histochemical method for the detection of 
the enzyme chloracetate esterase which is found in granulocytes,
including mast cells (tissue basophils)and their precursors.
(See:Leder LD Am J Dermatopathol 1979 Spring;1(1):39-42 
The chloroacetate esterase reaction. A useful means 
of histological diagnosis of hematological disorders 
from paraffin sections of skin.)

The Leder stain is a sensitive technique 
that is interpreted in the context of the 
clinicopathologic setting and correlation with 
the H+E morphology. In our experience, this is 
more sensitive and often easier to interpret 
than a Giemsa stain; although, we also 
do sometimes use the latter method as well. 

Immunohistochemical methods are also 
now available. (see below) We do not have 
any personal experience with those antibodies
currently.