Interstitial lung processes

Interstitial lung/pulmonary processes (IPP, also know as fibrotic lung processes) are immunopathological processes occurring at the level of the lung interstitium, i.e., in the interalveolar area, in the alveoli, and in the peribronchium. They prevent efficient gas exchange at the alveolar-capillary membrane and lead to respiratory insufficiency.

This is a group of diseases of various etiologies, which are characterized by varying degrees of inflammatory and / or fibrotic involvement of the lung parenchyma. Lung involvement is usually manifested by exertional dyspnea, weight loss, subfebrile illness, and more frequent respiratory infections. Cor pulmonale develops with signs of right heart decompensation in later stages.

Classification

 * 1) Diffuse lung processes resulting from known causes: exogenous allergic alveolitis (EAA), pneumoconiosis, post-radiation pneumonia, drug-induced lung damage (e.g., amiodarone and methotrexate);
 * 2) Idiopathic interstitial pneumonia: idiopathic pulmonary fibrosis (IPF); nonspecific interstitial pneumonitis; lymphocytic interstitial pneumonitis; desquamative interstitial pneumonitis; interstitial lung disease associated with respiratory bronchiolitis; cryptogenic organizing pneumonia; acute interstitial pneumonitis;
 * 3) Granulomatosis - sarcoidosis, pulmonary histiocytosis, granulomatosis with polyangiitis, vasculitis, etc...;
 * 4) Other: eosinophilic pneumonia, lymphangioleiomyomatosis, alveolar proteinosis, etc...

Pathogenesis
Fibrin deposition along the alveolar walls plays a role in the pathogenesis → so-called hyaline membranes are formed in the alveoli. This is followed by an inflammatory phase where there is infiltration by neutrophils (later macrophages and lymphocytes), which mediate repair processes resulting in fibrosis. Another pathogenetic event is alveolar cell proliferation, organization of fibrinous exudate, collagen deposition → repair / fibrosis.

Consequences of interstitial lung diseases

 * Hypoxemia (↓ p and O 2 ) especially during exertion in the initial stages with hyperventilation with a tendency towards respiratory alkalosis (↓ p and CO 2 );
 * later on, resting hypoxemia (↓ p and O 2 ) and hypoventilation manifest;
 * pulmonary hypertension → cor pulmonale.

Common features
Common features include exertional and then resting shortness of breath. IPPs are often accompanied by an irritating cough. Diagnostic imaging techniques reveal reticulonodulation or honeycomb lungs. During auscultation, crepitations can be heard.

Examination
In laboratory diagnostics, we choose examinations to exclude damage to other organs, basic immunological examinations, and examinations of autoantibodies. In indicated cases, exclusion of glomerular involvement, calcium metabolism, and serum angiotensin converting enzyme in patients with suspected sarcoidosis are indicated during clinical examination. It is important to examine lung function and respiratory parameters at rest, if necessary. A chest skiagram in two projections (however, a negative finding does not rule out IPP!) is necessary. Diagnostics high-resolution computed tomography (HRCT) is used to assess the type and extent of lung parenchyma involvement. In terms of invasive examinations, bronchoscopy with bronchoalveolar lavage, transbronchial biopsy, and a lung biopsy can be used if necessary.

Therapy
We choose therapy according to etiology (if known). The first step is to stop exposure to harmful inhalants.

Pharmacotherapy

 * systemic corticotherapy at doses appropriate to the severity of the disability
 * indications: idiopathic nonspecific interstitial pneumonitis (NSIP), severe exogenous allergic alveolitis (EAA), drug-induced lung disease, eosinophilic pneumonia, cryptogenic organizing pneumonia (COP), sarcoidosis with lung function impairment;
 * systemic corticosteroid therapy in combination with other immunosuppressants (e.g., methotrexate, azathioprine, cyclophosphamide)
 * systemic connective tissue diseases, other autoimmune syndromes;
 * N-acetylcysteine ​​- idiopathic pulmonary fibrosis (IPF),
 * proton pump inhibitors - IPF,
 * inhalation bronchodilators - silicosis, coal mine pneumoconiosis,
 * inhaled corticosteroids - sarcoidosis with bronchial hyperreactivity,
 * macrolides - some forms of organizing pneumonia.

Non-pharmacological treatment

 * oxygen therapy,
 * balneotherapy,
 * physiotherapy,
 * lung transplantation.

Prognosis
Idiopathic pulmonary fibrosis (IPF) has the most severe prognosis - lung transplantation, treatment with pirfenidone (immunosuppressant - suppresses fibroblast proliferation and production of proteins associated with fibrosis and cytokines, and also suppresses increased biosynthesis and accumulation of the extracellular matrix in response to cytokine growth factors).

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