Pathologists occasionally get asked to do mast cell stains, in a confusing 
clinical situation worth knowing about. (Usually an ordinary Giemsa stain 
suffices, though the low pH toluidine blue is obviously preferable if 
somebody is willing to do it.)

The clinical situation is an inflammatory disorder of the urinary bladder 
called interstitial cystitis. The disorder, 90% of whose patients are women, 
is characterized by urinary frequency and pain, and can be quite disabling.

Interstitial cystitis has evolved a considerable mythology, including the 
notion that the chronic inflammatory infiltrate contains numerous mast cells 
which when present in numbers are diagnostic of interstitial cystitis. 

This is bunk. The disease is real, but its pathologic picture is 
non-specific. The role of the pathologist is to ascertain that the patient 
doesn't actually have carcinoma in situ of the urinary bladder presenting as 
interstitial cystitis. This uncommon condition (more frequent in men) 
obviously requires totally different treatment.

Bob Richmond
Samurai Pathologist