Interstitial lung disease

Idiopathic

Idiopathic interstitial pneumonia is the term given to ILDs with an unknown cause. They represent the majority of cases of interstitial lung diseases (up to two-thirds of cases).^[10] They were subclassified by the American Thoracic Society in 2002 into 7 subgroups:^[11]

• Idiopathic pulmonary fibrosis (IPF): the most common subgroup, representing more than 30% of ILD^[8]
• Desquamative interstitial pneumonia (DIP)
• Acute interstitial pneumonia (AIP): also known as Hamman-Rich syndrome
• Nonspecific interstitial pneumonia (NSIP)
• Respiratory bronchiolitis-associated interstitial lung disease (RB-ILD)
• Cryptogenic organizing pneumonia (COP): also known by the older name bronchiolitis obliterans organizing pneumonia (BOOP)
• Lymphoid interstitial pneumonia (LIP)

Secondary

Secondary ILDs are those diseases with a known etiology, including:^{[citation needed]}

Pulmonary function testing

Most patients with suspected ILD are likely to undergo complete pulmonary function testing. These tests are useful in diagnosis and determining severity of the disease.^[16]

Although there is large diversity in interstitial lung disease, most follow a restrictive pattern. Restrictive defects are defined by decreased TLC (total lung capacity), RV (residual volume), FVC (forced vital capacity) and FEV1 (forced expiratory volume in one second). As both FVC and FEV1 are reduced, the FVC to FEV1 ratio remains normal or is increased.^[16]

As disease progression increases and the lungs become stiffer lung volumes will continue to decrease; lower TLC, RV, FVC and FEV1 scores are associated with a more severe disease progression and poorer prognosis.^[16]

X-ray and CT (computed tomography)

Chest radiography is usually the first test to detect interstitial lung diseases, but the chest radiograph can be normal in up to 10% of patients, especially early in the disease process.^[17][18]

High-resolution CT of the chest is the preferred modality and differs from routine CT of the chest. Conventional (regular) CT chest examines 7–10 mm slices obtained at 10 mm intervals; high resolution CT examines 1–1.5 mm slices at 10 mm intervals using a high-spatial-frequency reconstruction algorithm. The HRCT therefore provides approximately 10 times more resolution than the conventional CT chest, allowing the HRCT to elicit details that cannot otherwise be visualized.^[17][19]

Radiologic appearance alone, however, is not adequate and should be interpreted in the clinical context, keeping in mind the temporal profile of the disease process.^[17]

Interstitial lung diseases can be classified according to radiologic patterns.^[17]

Genetic testing

For some types of paediatric ILDs and few forms adult ILDs, genetic causes have been identified. These may be identified by blood tests. For a limited number of cases, this is a definite advantage, as a precise molecular diagnosis can be done; frequently then there is no need for a lung biopsy. Testing is available for

Oxygen therapy

Oxygen therapy at home is recommended in those with significantly low oxygen levels.^[20] Oxygen therapy in ILD is associated with improvements in quality of life but reductions in mortality are uncertain.^[8] Long-term oxygen therapy can be beneficial to people with ILD and hypoxemia to enhance gas exchange, lessen dyspnea, and increase physical activity.^[21]

Pulmonary rehabilitation

Pulmonary rehabilitation appears to be useful with the benefits being sustainable longer term with improvements in exercise capacity (as measured by a six minute walking test), dyspnea, and quality of life.^[22][8]

Lung transplantation

Lung transplantation is an option if the ILD progresses despite therapy in appropriately selected patients with no other contraindications.^[23][24] Life expectancy after lung transplant is 5.2 years in those with idiopathic interstitial pneumonias (including idiopathic pulmonary fibrosis) and 6.7 years in those with other types of ILD.^[8]

Medications

The antifibrotics pirfenidone and nintedanib have been shown to slow the decline in lung function (as measured by forced vital capacity [FVC]) in those with ILD compared to placebo.^[8] Pirfenidone was associated with a 45% less decline in FVC at 52 weeks compared to placebo in a trial involving people with idiopathic pulmonary fibrosis, and was associated with a slower FVC decline in those with progressive pulmonary fibrosis.^[25] Nintedanib was also associated with a slower FVC decline and increased mean survival in people with ILD.^[8]

The immunomodulator tocilizumab has a benefit in scleroderma associated ILD by helping to preserve lung function (as measured by FVC) at 48 weeks.^[8] The immunomodulators cyclophosphamide, mycophenolate mofetil and rituximab all showed improved lung function (as measured by % predicted FVC) compared to placebo in systemic sclerosis or scleroderma associated ILD.^[8]

The inhaled vasodilator treprostinil (a synthetic prostacyclin which acts as a prostaglandin I2 analogue) is indicated in the treatment of pulmonary hypertension secondary to interstitial lung disease and is associated with improved exercise capacity as measured by a 6-minute walk test.^[26]

Supportive care

Those with ILD should stop smoking cigarettes if they smoke. Vaccinations against pneumococcus, Covid-19, RSV and influenza are indicated in all those with ILD.^[8] Short acting opiates are known to improve breathlessness symptoms in those with end stage lung disease. The opiate agonist-antagonist nalbuphine and morphine are also known to improve coughing in those with ILD and other end stage lung diseases.^[8]