PTAH staining identifies rhabdomyosarcoma and requires mordanting in which fixatives if tissue was fixed in formalin?

• A. Zenker or Bouin
• B. Hematoxylin or eosin
• C. Neutral buffered formalin
• D. Mercuric chloride solution

Answer: (A)

PTAH staining relies on a mordant to allow the stain to bind to muscle tissue, revealing the characteristic features of rhabdomyosarcoma. When tissue has been fixed in formalin, a mordanting step is often needed because formalin alone can mask the tissue components PTAH binds to. Fixatives that provide this mordanting effect are Zenker’s and Bouin’s. Zenker’s fixative contains mercuric chloride, and Bouin’s contains picric acid; both create conditions that allow PTAH to form the staining complex with rhabdomyoblastic cross-striations, producing the distinct blue-black markings that identify rhabdomyosarcoma.

So, in formalin-fixed tissue, mordanting with Zenker’s or Bouin’s fixatives is used to optimize PTAH staining. Other options either are standard fixatives that don’t provide the mordant effect (neutral buffered formalin) or are not used alone as mordanting fixatives.