CD10: a valuable tool for the light microscopic diagnosis of microvillous inclusion disease (familial microvillous atrophy).

Microvillous inclusion disease (MID) is a specific disorder of the intestinal brush border that leads to intractable secretory diarrhea in infants. At present, electron microscopic analysis is required for its definitive diagnosis. However, this technique is not always available or feasible, and the diagnostic microvillous inclusions may not be evident in all specimens. Accordingly, the availability of a panel of histochemical and immunohistochemical stains displaying a specific staining pattern for MID will allow pathologists to reach a definitive diagnosis of this disorder without recourse to electron microscopy. CD10 is a membrane-associated neutral peptidase, shown to have a linear brush-border staining pattern in normal small intestine. We studied the staining pattern of CD10 in small intestinal biopsies from six patients with MID and in 24 control cases (10 normal small intestine, 10 celiac disease, two autoimmune enteropathy, and two allergic enteropathy). All MID cases revealed prominent cytoplasmic CD10 immunoreactivity in surface enterocytes. In contrast, all control cases showed linear brush-border staining. Similar results were obtained with periodic acid-Schiff, polyclonal carcinoembryonic antigen, and alkaline phosphatase, three stains known to show cytoplasmic staining of surface enterocytes in MID. In conclusion, CD10 is a valuable tool for the diagnosis of MID. It may be used as part of a panel that includes other stains with a distinctive staining pattern in MID such as periodic acid-Schiff, polyclonal carcinoembryonic antigen, and alkaline phosphatase. We suggest that the definitive diagnosis of MID can be reached when small bowel biopsies from infants with intractable diarrhea display cytoplasmic staining of surface enterocytes with the above-mentioned stains.