Focal Pulmonary Alveolar Proteinosis Is a Common Reaction and Progression Indicator in Idiopathic Pulmonary Fibrosis
Sayuri Nunomura, Tomonori Tanaka, Kyoko Otani, Kazuhiro Tabata, Yasuhiro Kondoh, Kensuke Kataoka, Takeshi Johkoh, Hiroyuki Taniguchi, Junya Fukuoka. Toyama University Hospital, Toyama, Japan; Tosei General Hospital, Seto, Japan; Kinki Central Hospital, Itami, Japan
Background: We have experienced cases of chronic interstitial pneumonia (IP) showing focal histologic features simulating pulmonary alveolar proteinosis (PAP). The occurrence and the meaning of focal PAP (fPAP) in the cases of chronic IP are unclear.
Design: 146 cases with chronic IP were selected from the consultation archive of Toyama University Hospital. Clinical records and histological specimens were reviewed. Immunohistochemical staining for fPAP; against surfactant protein-A (SP-A) was performed for unstained slides. Idiopathic pulmonary fibrosis (IPF) cases with fPAP were extracted and compared to the IPF cases without fPAP. Histological findings such as honeycomb cyst (HC), fibroblastic focus, and small airway disease were observed, and cases were separated to positive or negative based on the severity in each finding. Several statistical tests were performed depending on the distribution of the data.
Results: Twenty of 146 cases (13.7%) were identified to have fPAP [Figure A, B]. Focal PAP was strongly positive to SP-A [Figure C]. Among those 20 cases, 15 cases were IPF, and the incidence of fPAP in IPF patients was 15/56 (26.8%). In the comparison between IPF with and without fPAP, HC was solely associated with fPAP among histological findings (P = 0.016) [Table 1]. Furthermore, lower %FVC and higher serum KL-6 were associated with fPAP (P = 0.022, 0.005, respectively).
|fPAP (n=15)||No fPAP (n=21)||P value|
|Honeycomb cyst||13 (87%)||10 (47%)||0.016|
|Fibroblastic foci||12 (80%)||14 (67%)||0.468|
|Small airway disease||7 (47%)||15 (71%)||0.133|
|Cellular interstitial pneumonia||6 (40%)||5 (24%)||0.465|
|Dust deposition||4 (27%)||7 (33%)||0.729|
|Lymphoid follicle||5 (33%)||5 (24%)||0.709|