Interstitial pulmonary processes

Interstitial pulmonary processes (IPP, also fibrotizing pulmonary processes) are immunopathological processes at the level of the lungs interstitium, i.e. in the interalveolar region, in the alveoli and in the peribronchi. They prevent effective gas exchange on the alveolo-capillary membrane and lead to respiratory insufficiency.

It is a group of diseases of different 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 conditions and more frequent respiratory infections. In the late stages cor pulmonale develops with signs of right-sided heart decompensation.

Classification

 * 1) Diffuse lung processes from known causes: exogenous allergic alveolitis (EAA), pneumoconioses, post-radiation pneumonia, drug-induced lung damage (e.g. with 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) Granulomatoses − sarcoidosis, pulmonary histiocytosis from Langerhans cells, granulomatosis with polyangiitis and other vasculitides, etc.;
 * 4) Other: eosinophilic pneumonia, lymphangioleiomyomatosis, alveolar proteinosis, etc.

Pathogenesis
The deposition of fibrinalong the alveolar walls plays a role in the pathogenesis → so-called hyaline membranes are formed in the alveoli. This is followed by an inflammation phase with infiltration of neutrophils (later macrophages and lymphocytes), through which repair processes result in fibrosis. Another pathogenetic event is the proliferation of alveolar cells, the organization of fibrinous exudate, the deposition of collagen → repair / fibrosis.

Consequences of interstitial lung diseases

 * Hypoxemia (↓ paO2) especially exertional already in the initial stages with hyperventilation with a tendency to respiratory alkalosis (↓ paCO2);
 * later resting hypoxemia (↓ paO2) and hypoventilation;
 * pulmonary hypertension → cor pulmonale.

Common features
Common features include exertional and then resting dyspnea. ISTs are often accompanied by an irritating cough'. Reticulonodulations or honeycomb lungs may be visible on the skiagram. There may be crepitations in the listening findings.

Examination
In laboratory diagnostics, we choose tests to rule out damage to other organs, basic immunological tests, tests for autoantibodies. In indicated cases, as part of screening to exclude glomerular involvement, calcium metabolism and serum angiotensin-converting enzyme in patients with suspected sarcoidosis. It is important to examine lung functions and parameters of respiration at rest, or during exercise if possible and a skiagram of the chest in two projections' (a negative finding, however, does not rule out IPP!). We also use high-resolution computed tomography (HRCT) in the diagnosis to assess the type and extent of pulmonary parenchymal involvement. From invasive examinations, bronchoscopy with bronchoalveolar lavage and transbronchial biopsy will help us, or surgical lung biopsy eventually.

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

Pharmacotherapy
proton pump inhibitors – IPF,
 * systemic corticotherapy in doses corresponding to the severity of the disability
 * indications: idiopathic non-specific interstitial pneumonitis (NSIP), severe exogenous allergic alveolitis (EAA), drug-induced lung disease, eosinophilic pneumonia, cryptogenic organizing pneumonia (COP), sarcoidosis with lung function impairment;
 * systemic corticotherapy in combination with other immunosuppressants (e.g. methotrexate, azathioprine, cyclophosphamide)
 * systemic diseases of the connective tissue, other autoimmune syndromes;
 * N-acetylcysteine – idiopathic pulmonary fibrosis (IPF),
 * inhalational bronchodilation – silicosis, angler 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 serious prognosis – lung transplantation, eventually treatment with pirfenidone (immunosuppressant – suppresses fibroblast proliferation, production of cytokines and proteins associated with fibrosis and increased biosynthesis and accumulation of extracellular matrix in response to cytokine growth factors).