Pulmonary and Critical Care Medicine · Diffuse Parenchymal Lung Disease · study mode — pick an answer, then reveal.
Question · easy
A 55-year-old man with progressive exertional dyspnea and dry cough is found to have diffuse parenchymal lung disease (DPLD). When classifying his condition into the known-cause versus idiopathic categories, which of the following is classified as a DPLD of KNOWN cause?
The clinically useful classification divides DPLDs (overall prevalence ~70/100,000) into disorders with an identifiable cause and those that are idiopathic. Hypersensitivity pneumonitis is a known-cause DPLD: an immunologic response to repeatedly inhaled antigens (agricultural dusts, thermophilic fungi and bacteria, avian proteins), and identifying the trigger matters because antigen removal drives management. IPF and idiopathic NSIP are by definition idiopathic. Sarcoidosis — although granulomatous like hypersensitivity pneumonitis — has no identifiable trigger and is classified as unknown cause. Of note, the 2025 ERS/ATS update merges idiopathic and secondary interstitial pneumonias into one unified scheme, introducing bronchiolocentric interstitial pneumonia (BIP) as an airway-centered category (encompassing HP, CTD-ILD, aspiration, and drug-related patterns), renaming desquamative interstitial pneumonia as alveolar macrophage pneumonia (AMP), and replacing acute interstitial pneumonia with idiopathic diffuse alveolar damage (DAD).
A 62-year-old woman is evaluated for 8 months of dry cough and exertional dyspnea. Examination reveals fine end-inspiratory crackles at the lung bases. Her chest radiograph is reported as normal. Which of the following is the most appropriate next imaging study?
Noncontrast HRCT of the chest is the imaging modality of choice and standard of care in the initial evaluation of suspected DPLD — and a normal chest radiograph does NOT rule out DPLD. The plain film can be entirely normal in minimal or early disease (and reportedly in up to 20% of desquamative interstitial pneumonia cases), so clinical suspicion should trigger HRCT, not reassurance from a clear film. In the right clinical context HRCT can be diagnostic (sparing the patient biopsy), defines disease extent, flags advanced features such as honeycombing, and identifies the best biopsy targets when tissue is needed. CT pulmonary angiography evaluates pulmonary embolism, FDG-PET evaluates malignancy, and repeating the radiograph delays recognition of a potentially progressive fibrotic disease.
MKSAP 19 B.5 Ch.3; Harrison's 22e Ch.304
Question · medium
A 58-year-old man with subacute exertional dyspnea and nonproductive cough is being evaluated for suspected DPLD. His resting pulse oximetry is 96% on room air. Which of the following findings best reflects the diffusion limitation characteristic of DPLD?
Resting oximetry can be deceptively normal in DPLD; a desaturation of greater than 4% with ambulation reflects diffusion limitation — a physiologic hallmark of DPLD — so oximetry must be assessed with exertion, not only at rest. Complete PFTs (including lung volumes and DLCO) typically show a restrictive pattern: reduced total lung capacity with symmetrically reduced FEV1 and FVC, plus a reduced DLCO that may precede any fall in lung volumes. A low FEV1/FVC ratio indicates airflow obstruction, which is not the typical DPLD pattern (though obstructive or mixed deficits can occur in sarcoidosis, hypersensitivity pneumonitis, LAM, and smoking-related DPLD), and an increased TLC reflects hyperinflation from obstructive disease rather than interstitial fibrosis. Normal resting oximetry provides no evidence of diffusion limitation.
MKSAP 19 B.5 Ch.3; Harrison's 22e Ch.304
Question · medium
A 68-year-old man with chronic progressive exertional dyspnea undergoes HRCT of the chest, which shows subpleural, basal-predominant reticular abnormality with honeycombing and traction bronchiectasis. Which of the following is required before a confident diagnosis of idiopathic pulmonary fibrosis (IPF) can be made?
The HRCT description is a definite UIP pattern — but UIP is a pattern, not a diagnosis. Identical imaging and histology occur in CTD-associated ILD, asbestosis, and chronic hypersensitivity pneumonitis, so IPF remains a diagnosis of exclusion. ATS guidelines recommend serologic testing (CRP, ESR, antinuclear antibodies, rheumatoid factor, a myositis panel, and anti-CCP antibodies) to exclude CTD-associated DPLD even when the history and examination are silent, because autoantibodies such as anti-CCP can unmask an occult CTD before any extrapulmonary manifestations appear; a meticulous exposure history is equally essential. Immediate surgical biopsy is wrong: a definite UIP pattern — and, since the 2022 guideline, a probable UIP pattern — on HRCT in the appropriate clinical context is diagnostic of IPF without tissue confirmation, and surgical biopsy carries short-term mortality of up to ~5% (transbronchial lung cryobiopsy, with ~80% histologic yield vs ~95% for surgical biopsy, is a safer guideline-supported alternative in experienced centers when tissue is truly needed). Empiric corticosteroids are not treatment for IPF, and BAL with greater than 25% eosinophils suggests chronic eosinophilic pneumonia rather than confirming IPF.
A 61-year-old woman with fibrotic nonspecific interstitial pneumonia associated with rheumatoid arthritis is reassessed 1 year after her baseline evaluation. According to the 2022 ATS/ERS/JRS/ALAT guideline, which of the following findings meets the definition of progressive pulmonary fibrosis (PPF)?
PPF is a unifying label for any non-IPF ILD that worsens, defined as at least two of three criteria within one year: (1) worsening respiratory symptoms; (2) physiologic progression — absolute FVC decline ≥5% OR DLCO decline ≥10%; (3) radiologic progression. Worsening symptoms plus a 6% absolute FVC decline satisfies two criteria. Worsening dyspnea alone or radiologic progression alone satisfies only one criterion. The combination of a 3% FVC decline and an 8% DLCO decline satisfies none, because neither physiologic threshold (FVC ≥5%, DLCO ≥10%) is reached — and the two physiologic measures together count as a single criterion. Recognizing PPF matters therapeutically: the INBUILD trial showed that nintedanib slowed lung-function decline across a broad range of progressive fibrosing ILDs, and the 2022 guideline conditionally recommends nintedanib for PPF — making serial FVC and DLCO measurement a prerequisite for treatment decisions.