A 65-year-old man presented with a one-month history of cough, sputum and chest pain. He was a current smoker (20 cigarettes a day for 40 years) and reported no occupational exposure. His medical history was unremarkable. Symptoms persisted without medication.
At admission, temperature was 36.5  C, respiratory rate was 18/minute, and moist rales were heard in left lung.
Arterial blood gases at 21% FiO2 (fraction of inspiration O2) showed PaO2 (partial pressure of oxygen) 69 mmHg, PaCO2 (partial pressure of carbon dioxide in artery) 36 mmHg, pH 7.43.
Laboratory parameters were as follows:
White blood cell count of 7.99 x 109 cells/l [normal range (NR), 4-10 x 109 cells/l], differential neutrophil count of 69% (NR, 40-70%) and a C-reactive protein (CRP) level of 36.38 mg/l (NR, <10 mg/l). Serum electrolytes, renal and liver function tests were normal, as well as serological tests for tumor markers, Legionella pneumonia, Mycoplasma, Chlamydia, Coxiella psittaci, hepatitis C and B viruses, and HIV. Antinuclear antibody, perinuclear antineutrophil cytoplasmic antibody (P-ANCA), cytoplasmic-ANCA, and cyclic citrullinated protein antibody tests were negative.
High-resolution computed tomography (CT) demonstrated extensive shadows of high density in left lung, with bronchial ventilation sign, pleural thickening, and enlargement of lymph nodes in hilum and mediastinum. No abnormal enhancement was showed (Fig. 1). Lung cancer was considered by imaging diagnosis, without the exception of lymphatic metastasis.
Bronchofibroscope showed mucosa thickening and tracheobronchial stenosis in left lung (Fig. 2). Transbronchial biopsy indicated interstitial fibrous tissue hyperplasia and chronic inflammatory cell infiltration (Fig. 3A).
After 10 days antibiotic therapy with amoxicillin/clavulanic acid and roxithromycin, the symptom improved, but there was no significant change of CT sign. Percutaneous lung biopsy was arranged. Percutaneous biopsy from the left lower lobe also indicated interstitial fibrous tissue and chronic inflammatory cells without specificity (Fig. 3B).
One month later, the patient completed PET-CT (positron emission tomography-computed tomography) scan outside the hospital. The results showed high density shadow in left lung with increased metabolism, without obvious change in the range than before (Fig. 4). PET-CT indicated inflammation, without the exception of adenocarcinoma. Percutaneous biopsy was suggested again. The second percutaneous biopsy results was the same as above, showed interstitial fibrous tissue and chronic inflammatory cells.
Next, the patient visited Shanghai Chest Hospital, did EBUS-TBNA (endobroncheal ultrasonography-transbronchial needle aspirations) check. Pathology still suggested inflammatory. There were no characteristic pathological changes and definite diagnosis.
After four times pulmonary biopsies, there was no definitive pathological evidence. Also, there was no characteristic imaging finding. Other infectious diseases were less likely to be diagnosed based on the patient's clinical characteristics, tumor was the main differential diagnosis, but no tumor cells were found after multiple biopsies. The patient and his family defused to do further open lung biopsy, and the treatment could not be delayed. According to the clinical features, we diagnose OP in this case after excluding other diseases and gave corticosteroid therapy.
Oral corticosteroid therapy was started at 0.75mg/kg/day. Improvement of CT sign was observed after 1 month treatment, the shadow had dramatically decreased. Steroids were tapered over 6 months and lung CT scans significantly improved (Fig. 5). But new small shadow appeared, as the sign of recurrence (Fig. 5).
Once again, we persuaded the patient to do another biopsy. The patient underwent percutaneous biopsy again, and finally, the pathological manifestation indicated OP by finding granulation tissue plugs in the lumen of alveoli (Fig. 6). So far, the patient has been followed up for one year.
Informed consent was signed by the patient.