Background: We are occasionally presented with patients with unclassifiable interstitial pneumonia of unknown etiology. Idiopathic pulmonary upper lobe fibrosis (IPUF) does not fit any of the currently defined subsets of idiopathic interstitial pneumonias (IIPs). This study was performed to examine clinical, functional, and pathological characteristics of IPUF. Methods: We present 9 cases of histologically confirmed IPUF. The clinical and histological characteristics of the 9 patients were evaluated. The baseline respiratory function of all patients was measured. There were 7 patients whose forced vital capacity (FVC) had been monitored for at least a year who were selected to quantify the yearly decline in FVC. Results: All patients were slender, with a body mass index of 16.0-19.8kg/m2. Seven patients had a history of pneumothorax. Six patients died 1.8 to 5.7 years after the onset of the first symptoms. Fundamental histological features were intraalveolar collagen deposition and densely packed elastic fibers in the subpleural areas. These findings are the same as those seen in pleuroparenchymal fibroelastosis. However, the visceral pleura was thickened with dense collagen in only 2 patients, and pleural thickening was localized, if present, in the remaining 7 patients. Ventilatory impairment was also a characteristic. The time course decline of FVC was rapid and almost linear. The median yearly decline in FVC was -20.3% (range, -7.7% to -26.5%), which was more rapid than that reported for chronic fibrosing interstitial pneumonias such as idiopathic pulmonary fibrosis. Conclusions: IPUF is a unique pulmonary fibrosis that results in rapid deterioration of ventilatory function and poor prognosis.
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