BACKGROUND
{mosimage}On physical examination, his temperature is 100.9°F (38.3°C), his blood pressure is 160/90 mm Hg, and his heart rate is 110 bpm. The patient is breathing rapidly, with a respiratory rate of 30 breaths/min, and his oxygen saturation is 85% while breathing room air. The patient has no jugular venous distention or peripheral edema in the extremities. He does not have any digital clubbing. Auscultation of his chest reveals crackles in the left lower base.
An arterial blood gas (ABG) analysis taken while the patient is breathing room air shows a hemoglobin saturation of 80%, a partial pressure of oxygen of 48 mm Hg, a partial pressure of carbon dioxide of 35 mm Hg, and a pH of 7.50. On further laboratory investigation, the patient’s hemoglobin is 125 g/L (normal range, 136-173 g/L), his platelet count is 74 × 109/L (normal range, 166-383 × 109/L), and his white blood cell (WBC) count is elevated at 18.9 × 109/L (normal range, 4.8-10.5 × 109/L), with 83% granulocytes but no bands.
A chest radiograph demonstrates an infiltrate in the left lower lobe (see Image 1).
The patient is admitted to the hospital. Despite aggressive treatment for hypoxemia, including empiric use of antibiotics and oxygenation with noninvasive ventilation, respiratory failure develops, requiring the patient to undergo endotracheal intubation and mechanical ventilation. A computed tomography (CT) scan of the chest shows bilateral patchy, ground-glass infiltrates of an unclear etiology (see Image 2). A diagnostic fiberoptic bronchoscopy with bronchoalveolar lavage and transbronchial biopsy demonstrates diffuse fibrotic changes. Stains and cultures of the samples obtained at bronchoscopy fail to reveal a pathogen as the cause of this patient’s respiratory process.
No definitive etiology is identified. To what group of disorders does this condition belong?
HINT
Histopathologic examination of the transbronchial biopsy samples helps in making the diagnosis.
Authors:
Ryland P. Byrd, Jr, MD, Chief of Pulmonary Medicine, Medical Director of Respiratory Therapy, Quillen Mountain Home Veterans Affairs Medical Center; Professor, Department of Internal Medicine, Division of Pulmonary Diseases and Critical Care Medicine, James H. Quillen College of Medicine, East Tennessee State University
Said B. Iskandar, MD, Fellow in the Cardiology Division, Quillen College of Medicine, East Tennessee State University, Johnson City, Tenn.
eMedicine Editor::
Rick G. Kulkarni, MD, FACEP, Assistant Professor, Yale School of Medicine, Section of Emergency Medicine, Department of Surgery, Attending Physician, Medical Director, Department of Emergency Services, Yale-New Haven Hospital, CT
ANSWER
Desquamative interstitial pneumonia (DIP): Idiopathic interstitial pneumonias are a challenging group of diffuse parenchymal lung diseases (DPLDs). Regardless of their etiology, these pneumonias have a common pathophysiology that involves acute injury to the pulmonary parenchyma, leading to chronic interstitial inflammation and, ultimately, pulmonary fibrosis and tissue destruction.
{mosimage}A classification scheme published in a joint statement by the American Thoracic Society (ATS) and the European Respiratory Society (ERS) in 2001 emphasizes the importance of an integrated clinical, radiologic, and pathologic approach to the diagnosis of DPLDs. This categorization recognizes 7 entities: idiopathic pulmonary fibrosis/cryptogenic fibrosing alveolitis, nonspecific interstitial pneumonia, DIP, respiratory bronchiolitis interstitial lung disease, cryptogenic organizing pneumonia, acute interstitial pneumonia, and lymphoid interstitial pneumonia.1
DIP is a rare disorder that primarily affects people aged 30-50 years who smoke cigarettes. This condition is more common in men than in women by a ratio of 2:1. Typical symptoms of DIP include an insidious onset of dyspnea and a dry cough that develops over weeks or months and may progress to respiratory failure. About 50% of patients have digital clubbing, and progressive dyspnea on exertion is also common. The usual radiographic appearance reveals a diffuse ground-glass pattern in the middle and lower lung zones. An ABG analysis may reveal hypoxemia.5;6;7;3 The patient in this case fits the usual demographic profile and clinical presentation of DIP well.
Lung-function tests may demonstrate a restrictive ventilatory defect with decreased diffusional capacity and decreased pulmonary compliance.1 Long-term cigarette smoking is a recurrent feature that appears to be important for the pathogenesis of DIP in susceptible individuals. Respiratory infections, environmental exposures, collagen vascular diseases, drug reactions, malignancies, and, possibly, a genetic predisposition are also factors for developing DIP.5;6;7;3 The histopathology of DIP demonstrates diffuse accumulation of pigmented macrophages throughout the alveolar spaces, with an accentuated concentration in the peribronchial alveoli. The alveolar septa are thickened, with minimal inflammatory infiltration.4
The most effective treatment for DIP is glucocorticosteroid therapy. The typical initial dosage is oral prednisone at 40-60 mg/d for several months. If the therapeutic response is favorable, the dosage is slowly tapered to 15-20 mg/d or the equivalent alternate-day dosing. Glucocorticosteroids should be continued for at least 1 year.
The prognosis for patients with DIP is generally good. Most patients improve with smoking cessation and corticosteroid therapy.1 Cytotoxic agents, such as azathioprine and cyclophosphamide, are used as second-line drugs, usually in combination with oral glucocorticosteroids.1 Any exposure to inhalants or medications that may contribute to the patient’s condition should be discontinued. The overall 10-year survival rate for patients with DIP is 70%.4
This patient was treated with high-dose parenteral glucocorticosteroids. Within 24 hours of the start of this therapy, his hypoxemia improved. The patient was extubated 4 days after intravenous corticosteroids were initiated, and he was eventually discharged from the hospital with a tapering dosing regimen of oral prednisone. His chest radiographic findings returned to normal, and after 1 year of therapy, he was weaned off glucocorticosteroid therapy. Despite continuing to smoke cigarettes, the patient did not have a recurrence of DIP during a 2-year follow-up visit.
References:
1. American Thoracic Society, European Respiratory Society. American Thoracic Society/European Respiratory Society International Multidisciplinary Consensus Classification of the Idiopathic Interstitial Pneumonias. Am J Respir Crit Care Med 2002 Jan 15;165(2):277-304. [MEDLINE: 11790668]
2. Bjoraker JA, Ryu JH, Edwin MK, et al. Prognostic significance of histopathologic subsets in idiopathic pulmonary fibrosis. Am J Respir Crit Care Med 1998 Jan;157(1):199-203. [MEDLINE: 9445300]
3. Buchino JJ, Keenan WJ, Algren JT, Bove KE. Familial desquamative pneumonitis occurring in infants. Am J Genet Suppl. 1987;3:285-91. Review. [MEDLINE: 3130863]
4. Katzenstein AL, Myers JL. Idiopathic pulmonary fibrosis: clinical relevance of pathologic classification. Am J Respir Crit Care Med 1998 Apr;157(4 pt 1):1301-15. [MEDLINE: 9563754]
5. Nagai S, Hoshino Y, Hayashi M, Ito I.. Smoking-related interstitial lung diseases. Curr Opin Pulm Med 2000 Sep;6(5):415-9. Review. [MEDLINE: 10958232]
6. Ryu JH, Colby TV, Hartman TE, Vassallo R. Smoking-related interstitial lung diseases: a concise review. Eur Respir J 2001 Jan;17(1):122-32. Review. [MEDLINE: 11307741]
7. Tsukahara M, Yoshii H, Imamura T, Kamei T, Koga M, Furukawa S. Desquamative interstitial pneumonia in sibs. Am J Med Genet 1995 Dec 4;59(4):431-4. [MEDLINE: 8585561]
