Usual interstitial pneumonia (UIP)
This is the most frequent variant of the pathology, based on severe remodeling of the pulmonary interstitium.
Morphological changes of the interstitium:
- Thickening and reduplication of the endothelial and epithelial basement membranes occur.
- The amount of poorly degradable type IV and V collagens increases sharply.
- The air-blood barrier is infiltrated by inflammatory cells (histiocytes, lymphocytes), as well as fibroblasts and myofibroblasts.
Role of fibroblasts: They are localized not only in the barrier zone, but also penetrate between the thickened membranes (the "interposition" phenomenon) and extend into the lumens of capillaries and alveoli. This leads to obliteration of microvessels, a gas exchange block, and the development of pulmonary hypertension.
Intra-alveolar and epithelial changes: Protein exudate is organized within the alveolar lumen, Masson bodies are formed, and carnification develops. In late stages, normal type I pneumocytes are massively replaced by type II pneumocytes. The latter exhibit signs of cellular atypia and contain immature osmiophilic bodies, leading to impaired surfactant production, bronchiolar obliteration, and the appearance of foci of atelectasis.
The disease is often complicated by the development of cor pulmonale and progressive cardiopulmonary failure.
Nonspecific interstitial pneumonia (NSIP)
This form is difficult to diagnose because it lacks strictly specific morphological features and can occur in diseases of various etiologies.
Clinical presentation: Slowly progressive respiratory failure and increasing exertional dyspnea come to the forefront. Radiological findings reveal bilateral accentuation of the pulmonary pattern, predominantly in the basal zones.
Pathomorphology:
- The process has a "patchy" (mosaic) character: affected zones alternate with areas of preserved tissue.
- Unlike UIP, inflammatory changes (lymphohistiocytic infiltration) predominate here.
- Microvascular changes are pronounced, up to the development of destructive vasculitis and fibrinoid necrosis.
In the early stage, serous inflammation and edema are observed, which in later stages are replaced by moderately severe fibrosis. In general, NSIP is characterized by a relatively favorable course and high patient survival rates.
Desquamative interstitial pneumonia (DIP)
The disease begins gradually, with the average age of patients being about 43 years. The main difference of DIP is that the primary link in pathogenesis is damage to the alveolar epithelium, while the pulmonary interstitium is involved secondarily.
Stages of morphogenesis:
- Early stage: activated macrophages containing dark pigment granules accumulate in the alveolar lumens. The alveolar epithelium hyperplasticizes, becomes damaged, and desquamates (desquamation). Only moderate fibrosis and lymphocytic infiltration (sometimes with eosinophils) are noted in the interstitium.
- Late stage: interstitial sclerosis becomes more pronounced. Desquamated cells and macrophages accumulate in the alveoli. Gradually, only type II pneumocytes persist, and squamous cell metaplasia of the epithelium develops in 70% of cases.
In the late stages, tissues actively express markers: pancytokeratins, TGF-β, FGFb, Ki67.
Organizing pneumonia (COP)
Cryptogenic organizing pneumonia is a disease of undetermined etiology that clinically and radiologically mimics conventional infectious pneumonia. In literature, it is often found under the synonym BOOP (bronchiolitis obliterans organizing pneumonia).
Manifestations:
- The onset is subacute, accompanied by a pronounced dry cough.
- Fever is observed in 60% of patients.
- Radiographs show focal, "patchy" opacities that are persistent (do not disappear).
Briefly: answers to topical questions
What nosologies are included in the complete modern classification of idiopathic interstitial pneumonias?
The classification of idiopathic interstitial pneumonias includes the following clinicomorphological nosologies:
- Usual interstitial pneumonia — the most common variant.
- Nonspecific interstitial pneumonia — difficult to diagnose due to the lack of specific features.
- Desquamative interstitial pneumonia — characterized by primary damage to the alveolar epithelium.
- Organizing pneumonia — a disease of undetermined etiology.
- Acute interstitial pneumonia — corresponds to diffuse alveolar damage.
- Respiratory bronchiolitis-associated interstitial lung disease — associated with respiratory bronchiolitis.
- Lymphocytic interstitial pneumonia — a distinct form with lymphocytic infiltration.
What is the pathogenesis of Masson body formation in interstitial pneumonias?
The formation of Masson bodies occurs provided that the basement membrane remains intact. Pathogenesis includes the following sequential stages:
- Exudation — development of serous or serofibrinous exudate into the alveolar lumen.
- Organization — organization of the exudate and proteinaceous fluid directly within the alveolar lumen.
- Epithelialization — subsequent epithelialization of the organized exudate.
As a result of these processes, the exudate is replaced by connective tissue with the formation of Masson bodies, ultimately leading to carnification.
What macroscopic lung changes (cut surface appearance) are characteristic of the terminal stage of usual interstitial pneumonia?
The terminal stage of usual interstitial pneumonia is characterized by the formation of honeycomb-like structures ("honeycomb lung"). Macroscopically, there is induration of the lung tissue with a "rubbery" consistency, decreased aeration, and reduced elasticity.
For quick memorization of differences: UIP — Usual Interstitial Pneumonia (most common, severe fibrosis, cancer risk). DIP — Desquamation (epithelium suffers primarily, desquamates into alveoli). NSIP — Nonspecific Serous Interstitial Pneumonia (mosaic pattern, inflammation prevails over fibrosis).
Class and exam questions
What type of collagen accumulates in usual interstitial pneumonia?
There is a sharp increase in the specific gravity of poorly degradable type IV and V collagens in the pulmonary interstitium.
What is the primary pathogenetic link in the desquamative form (DIP)?
Unlike other forms, in DIP the alveolar epithelium is primarily damaged, while the pulmonary interstitium is involved secondarily.
Which cells mediate sclerosis in idiopathic fibrosing alveolitis?
The main effector cells responsible for the development of sclerosis are interstitial myofibroblasts and fibroblasts.
How does organizing pneumonia appear on a chest X-ray?
It is characterized by persistent, non-resolving focal "patchy" opacities.
What else to study on this topic
- Mechanism of Masson body formation and the process of carnification in UIP
- The phenomenon of fibroblast "interposition" between basement membranes
- Pathogenesis of cor pulmonale in interstitial fibrosis
- Squamous metaplasia of the alveolar epithelium in DIP
- Significance of immunohistochemical markers (TGF-β, FGFb, Ki67) in late stages of pneumonia
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