Interstitial lung disease / Lungs and rheumatic disease 4.4/5 (10)

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Interstitial lung disease (ILD) attacks the tissue in the lungs surrounding (interstitium) the air-containing ones air sacs (alveoli), so that lung function decreases. In some cases, the lung disease progresses and the lung tissue dies away over time. It is then replaced with scar tissue in the form of pulmonary fibrosis. Among the causes are infections, chemical substances and unknown, autoimmune mechanisms. In some cases, the lung disease is related to an underlying rheumatic disease in the form of systemic connective tissue disease, Vasculitis or Rheumatoid arthritis (arthritis). Disease of the pleura (pleuritis, pleural fluid) is discussed on a separate page.

Disease Causes

Disease in the lung tissue can be caused by infection, chemical damage, radiation damage, allergy, cancer or autoimmune disease (including rheumatic diseases). When an underlying condition cannot be found, the lung disease can be described as "idiopathic".


Signs of lung disease can develop acutely, over a few days, or insidiously, so that months pass before a person reacts. Shortness of breath, dry cough, pain in the lungs and exhaustion are often symptoms.


Medical history maps whether there are symptoms (see above) and at the same time signs of disease from the skin, muscles, joints, back and other internal organs such as the heart, oesophagus, stomach, intestines, kidneys). Other diseases and risk factors such as infections, drugs, chemical substances, radioactive radiation are requested.

Clinical assessed if there are signs of reduced oxygen uptake, such as bluish hands, feet, nose or ears and clubbing/hourglass nails on fingers. Crepitations on auscultation. Signs of right-sided heart strain: bone edema (water in the legs), congestion in the jugular veins. Joint inflammation (arthritis), skin changes and muscle weakness are examined.

Laboratory tests include lowering reaction (SR), C-reactive protein (CRP), Hemoglobin (often increased in chronic lung disease, may decrease in lung hemorrhage), white blood cells, platelets (high in inflammation, low values ​​may be due to pulmonary haemorrhage), liver and kidney function tests, creatine kinase (CK, myositis with lung changes?), metabolism/thyroid tests, antibody tests such as ANA (antinuclear antibody) with subgroups (ENA), antisynthetase antibody (myositis panel), anti-CCP and ANCA. Urine sample (stick for protein and erythrocytes).

Lung function tests (FEV1, FVC, DLCO). Spirometry is a subset of LFT and measures the amount (volume) of air that is exhaled and the flow rate (flow) of this air. Spirometry is therefore best suited to assess obstructive pulmonary disease such as asthma and COPD. Assessment of lung function in rheumatic diseases requires additional information about the lungs' ability to absorb oxygen. This is measured indirectly by DLCO (carbon monoxide diffusing capacity) which require more advanced equipment, most often in pulmonary wards in hospitals. Definition of severely impaired lung function is partly based on reduced values ​​in pulmonary function tests when FVC is less than 70% of expected and, together with DLCO, falls by 10% and 15% respectively per year. The degree of severity is also determined by age, other concurrent illnesses. if CT examinations show that more than 20% of the lungs have been attacked.

6-minute walking test measures how many meters you cover when you walk as fast as you can on flat ground within 6 minutes. The result reveals something about the physical form, including lung function. The test requires that one does not have physically reduced walking function for other reasons. The result varies from person to person. The test is therefore best suited to follow the performance of the individual over time. Distances of 400-700 m are considered normal for healthy people.

Imaging. A normal X-ray does not show small or incipient changes in the lung tissue. CT images are much more accurate and are therefore preferred. High Resolution CT (HRCT) presents the lung tissue well without using large doses of radiation. Fixed nodules (cancer-like) are best investigated with ordinary CT). NSIP og UIP are really lung-Tissue samples diagnoses, but suspicion is often also described on CT. The need for control of nodules in the lungs in adults can follow Fleischner's recommendations (reference: MacMahon H, 2017).

Bronchoscopy performed by pulmonologists who, via the nose or mouth, guide the bronchoscope down the trachea and on to the bronchi. The bronchoscope can be equipped with an ultrasound probe (endobronchial ultrasound = EBUS). A bronchoscope can be used to rinse bronchoalveolar lavage (BAL): Lavage fluid from the lungs is obtained via a bronchoscope for the diagnosis of infection (pneumocystis with several) and pulmonary haemorrhage.

Tissue sample (biopsy) is rarely necessary, but is used where it is necessary for the diagnosis, provided that one expects a therapeutic benefit. Classification of tissue samples (NSIP, UIP and more) is described here (Wikipedia, English). Open lung biopsy may be necessary if tissue changes are localized so that a transbronchial tissue sample is not possible and a closer assessment is necessary for the treatment.

Some concepts

Nonspecific interstitial pneumonitis (NSIP) is the most common manifestation in the lung tissue of those Systemic connective tissue diseases that Systemic sclerosis, Antisynthetase syndrome / myositis, hypersensitivity pneumonitis og Sarcoidosis. NSIP can be divided into two types, of which the inflammatory, inflammatory can be treated with corticosteroids such as prednisolone and other immunosuppressive drugs, while the fibrotic form is more permanent scar tissue. NSIP can be detected from medical history, clinical examination and CT images, but additional examinations to rule out infection, bleeding or cancer may be necessary in some cases. Tissue samples are not always necessary. The distribution of NSIP is even (homogeneous), patchy and can vary in distribution unlike UIP (see below). In the case of underlying rheumatic disease, NSIP and UIP most often begin in the lower (basal) parts of both lungs.

"Matt glass" (or "milk glass") is diffusely thickened lung tissue seen on CT examinations, to a lesser extent on plain X-rays. Ground-glass changes may be a transient condition and consistent with NSIP (see above) or an early stage on the way to fibrosis (see below). Infections, chemical exposure, allergic reactions and lung haemorrhages can also cause ground glass changes in the lungs.

Usual Interstitial Pneumonitis (UIP) are changes in the lung tissue that cannot be expected to reverse. UIP can follow from untreated NSIP (see above) or develop directly, as in idiopathic pulmonary fibrosis (IPF) which is the most common condition of pulmonary fibrosis. IPF also has the worst prognosis.

Lung fibrosis on x-ray
Lung fibrosis on X-ray. Illustration: Heilman J, MD. CC BY-SA 3.0,

UIP also occurs with far reaching Systemic connective tissue diseases: that Systemic sclerosis, Antisynthetase syndrome / myositis with multiple drug side effects, Sarcoidosis and inhaled harmful substances. During clinical examination, crackling sounds (crepitations) are detected over the lungs on auscultation. Also lung function tests shows reduced results in DLCO and FVC. Medicines (pirfenidone and nintedanib) have become available that can reduce the development of pulmonary fibrosis. Early diagnosis is therefore important.

Pumonary fibrosis: Connective tissue with no special function and which usually remains despite treatment.

Honeycombing: Widespread fibrosis (connective tissue) with cavities (cysts) in the lung tissue that resemble a honeycomb. Many cysts/cavities cause the lungs to lose their function.

Nodules (noduli) occurs in the lung tissue in various diseases and is detected incidentally in approx. 1% of all CT examinations, more often in various lung diseases. A large nodulus is 1-3 cm, small nodulus is less than 1 cm: Micronodulus is less than 3 mm. Micronodules are rarely malignant, but larger nodules must be assessed/followed up to rule out cancer. Fleischner recommendations (reference: MacMahon H, 2017). Other causes are infection and benign thickenings such as granulomas, small lymph nodes or varicose veins.

Ljuvenile cysts are round cavities that develop in place of normal lung tissue. If the cysts are numerous or large, lung function will be affected. In addition, lung cysts can burst and trigger a punctured lung (pneumothorax). Lymphoid interstitial pneumonia (LIP) is characterized by benign lymphocyte infiltrates, nodules and lymphoid follicles in the lung tissue. Often the changes are asymptomatic. CT images show multiple thin-walled cysts (Gupta N, 2016). LIP is typically seen in Sjögren's syndrome, Differential diagnoses in multiple lung cysts (adapted from Berger I et al, Journal of Medical Research, 2020).

DiagnosisCyst contourDistributionAdditional findings in the thorax
Lymphoid interstitial pneumonia (LIP)Round, oval, irregular. The size variesDiffuse peribroncovascular, subpleural, basalMattgalssfortetninger. Noduli in acute stages. Ev. Sjögren's syndrome
Lymphangioleiomyomatosis (LAM)Round, small. Irregular in advanced diseaseDiffuse, more centralEv. nodules. Matt glass densities. Chylothorax
Neurofibromatosis Complex (NFC)Round, smallDiffuse, fewNodules
Pulmonary Lung Cell Histiocytosis (PLCH)Round, oval, Irregular / bizarreUpper and middle lung fields. Recess of costophrenic angleSmall, star-shaped nodules. Varying thickness of cyst walls
Birt-Hogg-Dube Syndrome (BHD) Round, oval. Irregular. Varies in sizeMiddle and lower lung fields. Subpleurally, peribronovascularNo


The treatment options for lung disease depend entirely on the underlying cause of the lung disease. In case of infection it can be antibiotics against bacteria, in rheumatic inflammation prednisolone or other immunosuppressive treatment. There are also medicines for pulmonary fibrosis.

Regardless of the cause of illness and special treatment, the following applies:

  • Nicotine (smoking) must stop
  • Other concomitant diseases must be treated as best as possible, including:
    • Stomach acid reflux (acid reflux)
    • Heart disease
  • Obesity must be reduced

Interstitial lung disease (ILD) diseases (a selection)

Lung fibrosis on CT image
CT lungs: Fibrosis with honeycomb pattern (A). «Airtrapping» (B). The changes are seen in Idiopathic Pulmonary Fibrosis (IPF), Chronic Hypersensitivity Pneumonia (CHrHP) and in autoimmune rheumatic diseases. Smith M, J. Clin. Pathol. (2013). CC BY-NC 3.0


Pleuritis in rheumatic conditions, please read here

Lung disease and rheumatic diseases

Grans Compendium in Rheumatology

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