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Pneumonia, Diffuse Interstitial

For further information, see CMDT Part 9-21: Diffuse Interstitial Pneumonias

Key Features

Essentials of Diagnosis

  • Important to identify specific fibrosing disorders

  • Idiopathic disease may require biopsy for diagnosis

  • Accurate diagnosis identifies patients most likely to benefit from therapy

General Considerations

  • Historically, diagnosis was based on clinical and radiographic criteria, with lung biopsy uncommon

  • Several histologic patterns once grouped together as idiopathic pulmonary fibrosis (IPF) are now understood to represent different natural histories and responses to therapy

  • Evaluation must first identify patients whose disease is truly idiopathic (Table 9–17)

  • Most identifiable causes of interstitial lung diseases

    • Infectious

    • Environmental

    • Medication-related

    • Exposures

    • Associated with other medical conditions

  • A specific diagnosis allows providers to give accurate information on natural history and to distinguish patients most likely to benefit from treatment

  • Assessment of pulmonary hypertension is recommended in advanced disease

Table 9–17.Idiopathic interstitial pneumonias.
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Table 9–17. Idiopathic interstitial pneumonias.
Name and Clinical Presentation Histopathology Radiographic Pattern Response to Therapy and Prognosis

Usual interstitial pneumonia (UIP)

Age 55–60, slight male predominance. Insidious dry cough and dyspnea lasting months to years. Clubbing present at diagnosis in 25–50%. Diffuse fine late inspiratory crackles on lung auscultation. Restrictive ventilatory defect and reduced diffusing capacity on PFTs. ANA and RF positive in ~25% in the absence of documented collagen-vascular disease.

 Patchy, temporally and geographically nonuniform distribution of fibrosis, honeycomb change, and normal lung. Type I pneumocytes are lost, and there is proliferation of alveolar type II cells. “Fibroblast foci” of actively proliferating fibroblasts and myofibroblasts. Inflammation is generally mild and consists of small lymphocytes. Intra-alveolar macrophage accumulation is present but is not a prominent feature. Diminished lung volume. High-resolution CT scanning shows increased linear or reticular bibasilar and subpleural opacities, with associated honeycombing. Unilateral disease is rare. Minimal ground-glass. Areas of normal lung may be adjacent to areas of advanced fibrosis. No randomized study has demonstrated improved survival compared with untreated patients. Inexorably progressive. Median survival ~3 years, depending on stage at presentation. Nintedanib and pirfenidone reduce rate of decline in lung function. Refer early for lung transplantation evaluation.

Respiratory bronchiolitis–associated interstitial lung disease (RB-ILD)1

Age 40–45. Presentation like that of UIP though in younger patients. Similar results on PFTs, but less severe abnormalities. Patients with respiratory bronchiolitis are invariably heavy smokers.

 Increased numbers of macrophages evenly dispersed within the alveolar spaces. Rare fibroblast foci, little fibrosis, minimal honeycomb change. In RB-ILD the accumulation of macrophages is localized within the peribronchiolar air spaces; in DIP1, it is diffuse. Alveolar architecture is preserved. High-resolution CT shows nodular or reticulonodular pattern, more likely to reveal diffuse ground-glass opacities. Honeycombing is rare. May also show upper lobe emphysema. Spontaneous remission occurs in up to 20% of patients, so natural history unclear. Smoking cessation is essential. Prognosis clearly better than that of ...

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