The value of polyclonal carcinoembryonic antigen immunostaining in the diagnosis of microvillous inclusion disease.

Microvillous inclusion disease is a specific disorder recognized as a cause of intractable diarrhea of infancy. We studied three cases by light microscopy, electron microscopy, and immunostaining for polyclonal carcinoembryonic antigen (CEA). Histologically, all cases had villous atrophy and abnormal accumulation of periodic acid-Schiff-positive material in surface enterocytes. Ultrastructurally, poorly developed brush-border and intracytoplasmic inclusions lined by intact microvilli were present in surface enterocytes. Crypt cells showed well-preserved surface microvilli. Carcinoembryonic antigen immunostaining showed prominent intracytoplasmic reactivity in surface enterocytes and linear brush-border reactivity in crypt cells. Normal and diseased small bowel biopsy specimens used as controls revealed linear brush-border reactivity without intracytoplasmic staining. Intracytoplasmic positivity for carcinoembryonic antigen in microvillous inclusion disease is explained by its presence in the glycocalyx within the microvillous inclusions. The demonstration of a distinct staining pattern for polyclonal carcinoembryonic antigen in routinely processed small bowel biopsy specimens provides a new useful criterion that complements other established techniques for accurate diagnosis of microvillous inclusion disease.