Usual interstitial pneumonia (UIP) is a form of lung disease characterized by progressive scarring of both

lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...

s. The scarring ( fibrosis) involves the

pulmonary interstitium The interstitium is a contiguous fluid-filled space existing between a structural barrier, such as a cell membrane or the skin, and internal structures, such as organs, including muscles and the circulatory system. The fluid in this space is call ...

(the supporting framework of the lung). UIP is thus classified as a form of interstitial lung disease.

Terminology

The term "usual" refers to the fact that UIP is the most common form of interstitial fibrosis. "Pneumonia" indicates "lung abnormality", which includes fibrosis and inflammation. A term previously used for UIP in the British literature is cryptogenic fibrosing alveolitis (CFA), a term that has fallen out of favor since the basic underlying pathology is now thought to be fibrosis, not inflammation. The term usual interstitial pneumonitis (UIP) has also often been used, but again, the ''-itis'' part of that name may overemphasize inflammation.

Signs and symptoms

The typical symptoms of UIP are progressive shortness of breath and cough for a period of months. In some patients, UIP is diagnosed only when a more acute disease supervenes and brings the patient to medical attention.

Causes

The cause of the scarring in UIP may be known (less commonly) or unknown (more commonly). Since the medical term for conditions of unknown cause is "idiopathic", the clinical term for UIP of unknown cause is idiopathic pulmonary fibrosis (IPF). Examples of known causes of UIP include connective tissue diseases (primarily rheumatoid arthritis), drug toxicity, chronic hypersensitivity pneumonitis, asbestosis and Hermansky–Pudlak syndrome.

Diagnosis

UIP (Usual interstitial pneumonia)-CT scan

UIP may be diagnosed by a radiologist using computed tomography (CT) scan of the chest, or by a pathologist using tissue obtained by a lung biopsy.

Radiology

Radiologically, the main feature required for a confident diagnosis of UIP is honeycomb change in the periphery and the lower portions (bases) of the lungs. On high-resolution computed tomography (HRCT), the following categories, depending on imaging findings, have been recommended by a collaborative effort by the American Thoracic Society, European Respiratory Society, Japanese Respiratory Society, and the Latin American Thoracic Society: *UIP pattern: :*

Honeycombing Honeycombing or "honeycomb lung" is the radiological appearance seen with widespread fibrosis and is defined by the presence of small cystic spaces with irregularly thickened walls composed of fibrous tissue. Dilated and thickened terminal and r ...

, with or without peripheral traction

bronchiectasis Bronchiectasis is a disease in which there is permanent enlargement of parts of the bronchi, airways of the lung. Symptoms typically include a chronic cough with sputum, mucus production. Other symptoms include shortness of breath, hemoptysis, co ...

; or bronchiolectasis (dilatation of the terminal bronchioles) :*Predominantly subpleural and basal :*Often heterogenous distribution, being occasionally diffuse, and may be asymmetrical There may be superimposed CT features such as mild

ground-glass opacity Ground-glass opacity (GGO) is a finding seen on chest x-ray (radiograph) or computed tomography (CT) imaging of the lungs. It is typically defined as an area of hazy opacification (x-ray) or increased attenuation (CT) due to air displacement by ...

, reticular pattern and pulmonary ossification. *Probable UIP pattern: :*Predominantly subpleural and basal :*Often heterogenous distribution :*Reticular pattern with peripheral traction bronchiectasis or bronchiolectasis :*There may be mild ground-glass opacity *Indeterminate for UIP: :*Predominantly subpleural and basal :*Subtle reticular pattern :*May have mild ground-glass opacity or distortion (“early UIP pattern”) *Findings suggestive of another diagnosis, including: :*Other predominant distribution: ::*Peribronchovascular ::*Perilymphatic ::*Upper or mid-lung :*Cysts :*Marked mosaic pattern :*Predominant ground-glass opacity :*Profuse lung micronodules :* Lung nodules, especially centrilobular :*Consolidation :* Pleural plaques (indicating asbestosis) :*Dilated esophagus (indicating connective tissue disease) :*Distal clavicular erosions (indicating rheumatoid arthritis) :*Extensive lymph node enlargement :* Pleural effusion :*Pleural thickening (indicating connective tissue disease/drugs)

Histology

The histologic hallmarks of UIP, as seen in lung tissue under a microscope by a pathologist, are interstitial fibrosis in a "patchwork pattern", honeycomb change and fibroblast foci (see images below). Image:UIPlungbiopsy.jpg, Appearance of usual interstitial pneumonia (UIP) in a surgical lung biopsy at low magnification. The tissue is stained with hematoxylin (purple dye) and eosin (pink dye) to make it visible. The pink areas in this picture represent lung fibrosis (collagen stains pink). Note the "patchwork" (quilt-like) pattern of the fibrosis. Image:Honeycomb change.jpg, Appearance of honeycomb change in a surgical lung biopsy at low magnification. The dilated spaces seen here are filled with mucin. Hematoxylin-eosin stain, low magnification. Image:Fibroblast focus.jpg, A fibroblast focus in a surgical lung biopsy of UIP. Hematoxylin-eosin stain, high magnification. The white space to the left is an airspace. The pale area to the right is a fibroblast focus. It is an area of active fibroblast proliferation within the interstitium of the lung.

Differential diagnosis

The differential diagnosis includes other types of lung disease that cause similar symptoms and show similar abnormalities on chest radiographs. Some of these diseases cause fibrosis, scarring or honeycomb change. The most common considerations include: * chronic hypersensitivity pneumonitis * non-specific interstitial pneumonia * sarcoidosis * pulmonary Langerhans cell histiocytosis * asbestosis

Management

Oxygen therapy Oxygen therapy, also known as supplemental oxygen, is the use of oxygen as medical treatment. Acute indications for therapy include hypoxemia (low blood oxygen levels), carbon monoxide toxicity and cluster headache. It may also be prophylactica ...

may assist with daily living. In case of idiopathic pulmonary fibrosis, certain medications like nintedanib and pirfenidone can help slow the progression. Lastly,

lung transplants Lung transplantation, or pulmonary transplantation, is a surgical procedure in which one or both lungs are replaced by lungs from a donor. Donor lungs can be retrieved from a living or deceased donor. A living donor can only donate one lung lobe. ...

may help.

Prognosis

Regardless of cause, UIP is relentlessly progressive, usually leading to respiratory failure and death without a lung transplant. Some patients do well for a prolonged period of time, but then deteriorate rapidly because of a superimposed acute illness (so-called "accelerated UIP"). The outlook for long-term survival is poor. In most studies, the

median In statistics and probability theory, the median is the value separating the higher half from the lower half of a data sample, a population, or a probability distribution. For a data set, it may be thought of as "the middle" value. The basic fe ...

survival is 3 to 4 years. Patients with UIP in the setting of rheumatoid arthritis have a slightly better prognosis than UIP without a known cause (IPF).

History

UIP, as a term, first appeared in the pathology literature. It was coined by Averill Abraham Liebow.

References

External links

{{Respiratory pathology Pneumonia