Niemann-Pick disease (types A and B), or acid sphingomyelinase deficiency, is an 
inherited deficiency of acid sphingomyelinase, resulting in intralysosomal 
accumulation of sphingomyelin in cells throughout the body, particularly within 
those of the reticuloendothelial system. These cellular changes result in 
hepatosplenomegaly and pulmonary infiltrates in humans. A knockout mouse model 
mimics many elements of human ASMD and is useful for studying disease 
histopathology. However, traditional formalin-fixation and paraffin embedding of 
ASMD tissues dissolves sphingomyelin, resulting in tissues with a foamy cell 
appearance, making quantitative analysis of the substrate difficult. To optimize 
substrate fixation and staining, a modified osmium tetroxide and potassium 
dichromate postfixation method was developed to preserve sphingomyelin in 
epon-araldite embedded tissue and pulmonary cytology specimens. After 
processing, semi-thin sections were incubated with tannic acid solution followed 
by staining with toluidine blue/borax. This modified method provides excellent 
preservation and staining contrast of sphingomyelin with other cell structures. 
The resulting high-resolution light microscopy sections permit digital 
quantification of sphingomyelin in light microscopic fields. A lysenin affinity 
stain for sphingomyelin was also developed for use on these semi-thin epon 
sections. Finally, ultrathin serial sections can be cut from these same tissue 
blocks and stained for ultrastructural examination by electron microscopy.