Radiological presentation and course of DAD
Drug-induced diffuse alveolar damage typically develops several weeks or months after initiating therapy (e.g., with EGFR inhibitors or PD-1 immune checkpoint inhibitors). Clinically, the process begins with steadily progressive dyspnea.
On plain radiographs, changes are identical to the presentation of acute respiratory distress syndrome (ARDS). Bilateral homogeneous or patchy airspace consolidation is determined in the middle and lower lung zones.
High-resolution computed tomography (HRCT) visualizes:
- Extensive bilateral areas of decreased attenuation in the form of ground-glass opacities.
- Gravitationally dependent consolidation of lung tissue (dependent consolidation).
Severe forms of DAD can evolve into acute interstitial pneumonia (AIP). In the early stages of this transition, diffuse ground-glass opacities persist, but subplacental spaces remain unaffected. After approximately two months, transformation into fibrosis begins, accompanied by the formation of traction bronchiectasis. There are no specific histological signs of drug-induced injury per se, so the diagnosis is made by exclusion (primarily ruling out opportunistic infections).
Nonspecific interstitial pneumonia (NSIP)
The NSIP pattern is the most frequent variant of drug-induced lung injury. It can be triggered by amiodarone, methotrexate, simvastatin, busulfan, phenytoin, carmustine, and targeted agents.
The tomographic picture completely replicates idiopathic NSIP. The disease progresses to focal fibrosis with a peribronchovascular distribution (reticular pattern and traction bronchiectasis appear).
Interesting fact: when taking nitrofurantoin, HRCT signs visually consistent with irreversible fibrosis may sometimes completely resolve after drug discontinuation.
A special place is occupied by amiodarone-induced injury:
- NSIP is its most frequent manifestation.
- HRCT reveals ground-glass opacities with fine intralobular reticular changes (more often peripherally), and less frequently, foci of organizing pneumonia.
- Specific marker: abnormally high X-ray attenuation values in lung tissue and the liver. This is due to the direct physical deposition of an iodine-containing drug.
Organizing and eosinophilic pneumonias
In addition to DAD and NSIP, drug toxicity can manifest with two other characteristic patterns.
Organizing pneumonia (OP) is associated with methotrexate, bleomycin, gold salts, cyclophosphamide, and nitrofurantoin. HRCT reveals bilateral focal consolidation areas, nodules, or masses that may be distributed asymmetrically. Ground-glass opacities and consolidations have a predominantly peripheral or peribronchiolar distribution.
Eosinophilic pneumonia occurs during treatment with NSAIDs, PAS, sulfasalazine, and methotrexate. Histologically, it manifests as an accumulation of eosinophils in the alveoli and interstitial infiltration.
| Characteristic | Features of eosinophilic pneumonia |
|---|---|
| Laboratory data | Blood eosinophilia is present in only 40% of patients |
| CT localization | Predominantly upper lobes and peripheral regions |
| Type of lesion | Bilateral airspace consolidation |
The main diagnostic challenge is the targeted search for these patterns in at-risk patients presenting with diffuse opacities of unclear origin.
Briefly: answers to topical questions
What are the morphological stages in the presentation of diffuse alveolar damage (DAD)?
- Early phase (fase) — interstitial edema of the parenchyma, inflammatory exudation into the alveolar lumen, hyaline membrane formation, capillary thrombosis.
- Late stages (fase) — usually after the 2nd week, signs of intra-alveolar and/or interstitial organization appear, associated with type II pneumocyte proliferation.
For quick memorization of the four main patterns of drug-induced lung injury, use the acronym ENDO: Eosinophilic pneumonia, NSIP, DAD, Organizing pneumonia.
Class and exam questions
On CT, it looks like classic irreversible fibrosis with reticular changes, but these manifestations may completely resolve after drug withdrawal.
On CT, it looks like classic irreversible fibrosis with reticular changes, but these manifestations may completely resolve after drug withdrawal.
High X-ray attenuation values of the lung parenchyma and liver tissue on CT, caused by the direct deposition of iodine-containing amiodarone in organs.
High X-ray attenuation values of the lung parenchyma and liver tissue on CT, caused by the direct deposition of iodine-containing amiodarone in organs.
No, despite pronounced eosinophilic infiltration of the alveoli, peripheral blood eosinophilia is observed in only about 40% of patients.
No, despite pronounced eosinophilic infiltration of the alveoli, peripheral blood eosinophilia is observed in only about 40% of patients.
What else to study on this topic
- Pathophysiology of acute interstitial pneumonia (AIP) development from DAD
- Differential radiodiagnosis between drug-induced DAD and severe viral pneumonias
- Radiological semiotics of idiopathic NSIP
- Mechanisms of traction bronchiectasis formation in interstitial lung diseases
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