Desquamation Interstitial Pneumonia Presenting as a Solid Mass in the Lung: a Case Report.

Background: Desquamation interstitial pneumonia (DIP) is a rare type of idiopathic interstitial pneumonia. High resolution computed tomography (HRCT) shows ground glass opacities without the peripheral reticular opacities characteristic of usual interstitial pneumonia (UIP). Here we report a case of DIP presenting as a solid mass in the lung, which is rarely described in the literature. Case presentation: A 77-year-old man presented with dry cough and dyspnea on exertion for one month was admitted to our hospital. The lung CT scan showed there was a pulmonary mass in right lower lung and the patient was scheduled for surgery. He was a sculpture artist, non-smoker and the previous medical history included only mandatory spondylitis without other connective tissue diseases. Nine days post-last CT, the FDG PET/CT demonstrated the mass in the right lower lung was signicantly hypermetabolic (SUV value=8.9) but inammatory exudate could be observed around the mass. We gave antibiotics and performed CT-guided percutaneous lung biopsy. The result showed that there were a large number of macrophages in the alveolar cavity, alveolar epithelial type II cells hyperplasia in some areas and chronic inammation was noted in the interstitium. Then the desquamative interstitial pneumonia was diagnosed. We gave the patient glucocorticoid therapy, then the patient's symptoms disappeared gradually and the lung CT showed that the pulmonary mass was disappeared. Conclusions: Our report illustrates the rare presentation of DIP. Furthermore, for the pulmonary mass, even if appeared hypermetabolic on PET/CT, it is still necessary to make a denite pathological diagnosis before operation, so as to reduce the damage to patients.

was admitted to our hospital. The lung CT scan showed there was a pulmonary mass in right lower lung and the patient was scheduled for surgery. He was a sculpture artist, non-smoker and the previous medical history included only mandatory spondylitis without other connective tissue diseases. Nine days post-last CT, the FDG PET/CT demonstrated the mass in the right lower lung was signi cantly hypermetabolic (SUV value=8.9) but in ammatory exudate could be observed around the mass. We gave antibiotics and performed CT-guided percutaneous lung biopsy. The result showed that there were a large number of macrophages in the alveolar cavity, alveolar epithelial type II cells hyperplasia in some areas and chronic in ammation was noted in the interstitium. Then the desquamative interstitial pneumonia was diagnosed. We gave the patient glucocorticoid therapy, then the patient's symptoms disappeared gradually and the lung CT showed that the pulmonary mass was disappeared.
Conclusions: Our report illustrates the rare presentation of DIP. Furthermore, for the pulmonary mass, even if appeared hypermetabolic on PET/CT, it is still necessary to make a de nite pathological diagnosis before operation, so as to reduce the damage to patients.

Background
Desquamation interstitial pneumonia (DIP) is a rare type of idiopathic interstitial pneumonia and the incidence only accounts for about 10-17% [1]. The vast majority (>90 percent) of patients with DIP are smokers, a small percentage of cases are associated with rheumatic diseases [2]. High resolution computed tomography (HRCT) shows ground glass opacities without the peripheral reticular opacities characteristic of usual interstitial pneumonia (UIP) [3]. Here we report a case of DIP presenting as a solid mass in the lung.

Case Report
A 77-year-old man presented with dry cough and dyspnea on exertion for one month was admitted to our hospital. The lung CT scan showed there was a pulmonary mass in right lower lung and the patient was scheduled for surgery. He was a sculpture artist and non-smoker. The previous medical history included only mandatory spondylitis without other connective tissue diseases. His admitted physical examinations revealed vital signs were within normal limits. There were no cyanosis on lips, no clubbing and no super cial swollen lymph node being palpable. Breath sounds were decreased on the right lower side.
Physical examinations of cardiovascular system and abdomen were normal. Blood chemistry showed almost normal white cell count, procalcitonin (PCT) and C-reactive protein (CRP). Erythrocyte sedimentation rate was 77 mm/1st h. The human leukocyte antigen-B27 (HLA-B27) antibody was mildly elevated. Among the autoimmune disease markers (C3, C4, rheumatoid factor, antinuclear antibody, antineutrophil cytoplasmic antibodies, anti-cardiolipin antibody, anti-dsDNA, anti-Sm, anti-SSA, anti-SSB, anti SCL-70, anti Jo-1, and anti-RNP/Sm antibodies) and immunoglobulin G, A, and M were all normal. Tumor markers (CA199, f-PSA, ProGRP, PSA, CEA, SCC, CYFRA21-1, CA242, CA125, NSE, CA153, CA724, CA50) were only SCCA 12.6 ng/ml (range, 0-2.5 ng/mL). Pulmonary function tests showed that the patient had mild restrictive ventilatory dysfunction and mild diffusion dysfunction. Nine days post-last CT, the FDG PET/CT demonstrated the mass in the right lower lung was signi cantly hypermetabolic (SUV value=8.9) but in ammatory exudate could be observed around the mass. We gave antibiotics and performed PET/CT-guided percutaneous lung biopsy. The result showed that there were a large number of macrophages in the alveolar cavity, alveolar epithelial type II cells hyperplasia in some areas and chronic in ammation was noted in the interstitium (see Figure 2). Then the desquamative interstitial pneumonia was diagnosed. Methylprednisolone intravenous drip of 40 mg per day for 2 weeks were performed. After that, the treatment was converted to 40 mg of oral prednisone per day. The patient's symptoms disappeared gradually and the lung CT showed that the pulmonary mass was decreased in size (see Figure 1). The patient's symptoms were resolved, and he was discharged with 40 mg of oral prednisone per day. The dose of prednisone was reduced by 5 mg weekly until to 20 mg. Then the dose was reduced by 5 mg monthly until to 10 mg and maintained for three months. The total course of treatment was half a year. The lung mass signi cant shrink was observed after discharged about one month and eventually disappeared. (see Figure 1).

Discussion
The exact etiology of the DIP is uncertain but 58-91% of DIP cases are linked with cigarette smoking [4,5].
In addition, the DIP may be associated with harmful irritating substances from environmental/occupational (such as asbestos, talc, graphite, silica and aluminum), systemic disease virus infection and drugs [6,7]. The main histopathological feature of DIP is a large number of macrophages in alveoli, which were usually diffusely distributed throughout the pulmonary acini within alveoli, and proliferation of pneumocytes over the course of alveolar septa [8]. Although there may be mild in ltration of in ammatory cells in the alveolar septum, the alveolar structure generally remained normal. The in ltrating in ammatory cells include a small number of eosinophils, accompanied by broblast proliferation. The rare changes are mild brosis, but severe brosis and honeycomb like lesions are very rare.
Pathological diagnosis is the "gold standard" for the diagnosis of DIP. Methods of lung biopsy included transbronchial lung biopsy (TBLB), CT-guided percutaneous needle biopsy, transbronchial cryobiopsy and surgical lung biopsy. Lung specimens from TBLB are too small, which can't fully re ect the scope and degree of lung lesions and satisfy the diagnosis of interstitial lung disease. The specimens from surgical lung biopsy can meet the diagnostic requirements of interstitial lung disease, but the surgical lung biopsy is costly and traumatic, which is not easy for patients to accept. Transbronchial cryobiopsy or CT-guided percutaneous lung biopsies have fewer healthcare costs, fewer traumatic, and the specimens can meet the diagnostic requirements of interstitial lung disease, which is easy for patients to accept. This patient underwent percutaneous lung biopsy and the result showed that there were a large number of macrophages in the alveolar cavity and chronic in ammation was noted in the interstitium, so it could be diagnosed as DIP. At the same time, the patient had no history of smoking or second-hand smoke, which was rare in the literature. The patient was a sculptor. Because the environmental or occupational exposure may be one of an etiological risk factors, it is speculated that dust inhalation may be one of the inducing factors in this case. However, because the specimens were relatively small, it was impossible to know whether there was dust deposition in other lesions regions.
The special feature of this case was lung CT, which showed a single solid mass in the right lower lung, and then rapidly progressed with peripheral infection. However, the typical imaging manifestation of DIP is diffuse ground glass shadow in both lungs, which is located under the pleura. The lower lung is more than the upper lung, and some are accompanied by linear opacities and reticulation in the base [9]. Honeycomb appearance is uncommon. Therefore, the imaging ndings of this case were different from the typical imaging ndings of DIP, which were rarely reported in the literature. These imaging ndings were often misdiagnosed as pulmonary malignant tumor because of PETCT demonstrated hypermetabolism and the patients were usually treated by surgery. Therefore, for the pulmonary mass, even if PETCT indicates hypermetabolic lesions and highly suspected tumor, the pathological diagnosis of preoperative mass is still very important to avoid irreversible damage to patients.
The main treatment is to quit smoking and glucocorticoid therapy and some cases become spontaneous remission after quitting smoking. Glucocorticoids have been reported to be bene cial in case series, although improvement may be temporary [3]. Environmental/occupational factors are also suspicious etiology of DIP [6,7]. That DIP improved in two cases after leaving the workplace without steroid treatment was reported by Lougheed et al [7]. Therefore, It is reasonable to terminate any possible environmental risk factors. Initial glucocorticoid therapy consists of 40-60 mg/day for 6 weeks, then decreased gradually and stopped within 6-9 months. Glucocorticoid therapy of this case: intravenous methylprednisolone 40mg for 2 weeks, oral prednisone 40mg for 3 weeks, and then decrease 5 mg weekly until to 20 mg. Then the dose was reduced by 5 mg monthly until to 10 mg and maintained for three months. The total course of treatment was half a year. The case clinical symptoms and radiology were signi cant improvement after steroid treatment.

Conclusions
The imaging ndings of such a case are rarely described in the literature. There is no smoking history and it is easy to be misdiagnosed as tumor. However, all of these clinical characteristics mentioned above are uncommon. Therefore, we still know little about this rare interstitial lung disease, and we still need more clinical cases, more complete clinical imaging and pathology to enrich our understanding of the disease. At the same time, for the pulmonary mass, even if appeared hypermetabolic on PET-CT, it is still necessary to make a de nite pathological diagnosis before operation, so as to reduce the damage to patients.
Abbreviations DIP: Desquamation interstitial pneumonia; HRCT: High resolution computed tomography; UIP: usual interstitial pneumonia; PCT: procalcitonin; CRP: and C-reactive protein; HLA-B27: human leukocyte antigen-B27; TBLB: transbronchial lung biopsy; Declarations Figure 1 The patient's symptoms disappeared gradually and the lung CT showed that the pulmonary mass was decreased in size Figure 2