Respiratory failure due to micronodular type II pneumocyte hyperplasia

Aims: To report the first case of respiratory failure due to micronodular type II pneumocyte hyperplasia. Methods adn results: Biopsy, explant and autopsy material from a 16-year-old girl, a smoker, with no personal or family history of tuberous sclerosis, who died following lung transplantation necessitated by progressive respiratory failure, was evaluated histologically. Micronodular pneumocyte hyperplasia was identified histologically as the cause of the respiratory failure. Foci of hyperplastic type II pneumocytes measuring up to 4 mm were widely scattered through the lungs. The hyperplastic cells had abundant eosinophilic cytoplasm, vesicular nuclei and prominent nucleoli. Immunohistochemistry showed that they stained for cytokeratins AE1, AE3 and CAM 5.2 and for epithelial membrane antigen (EMA), but not for carcinoembryonic antigen (CEA), S100, smooth muscle actin, CD68 and HMB-45. Conclusions: Although micronodular type II pneumocyte hyperplasia is usually of no clinical significance, in our patient the process was so florid as to cause respiratory failure, which was severe enough to necessitate lung transplantation.