Microvillous inclusion disease with abundant vermiform, electron-lucent vesicles.

A 3-month-old girl with congenital secretory diarrhea underwent a duodenal biopsy. Histologic study showed villous atrophy and large amounts of PAS-positive material within enterocyte cytoplasm. Despite a clinical suspicion of microvillous inclusion disease, 2 sessions of electron microscopy were unsuccessful in detecting the diagnostic inclusions. Instead, large aggregates of electron-lucent, vermiform membranous vesicles were observed in enterocyte cytoplasm, corresponding to the PAS-positive material. A third attempt at electron microscopy was successful in detecting small numbers of microvillous inclusions. These and other recently reported cases document an expanding spectrum of ultrastructural findings in this disease, including examples where the classic microvillous inclusions are overshadowed by other features.