Usual interstitial pneumonia

Usual interstitial pneumonia
Diagnosis in short
Fibroblast focus in usual interstitial pneumonia. H&E stain.
LM	fibroblast foci, interstitial inflammation, microscopic honeycombing (typically peripheral & lined by ciliated epithelium), spatial heterogeneity - patchy lesional distribution (areas of abnormal and normal lung may appear beside one another), temporal heterogeneity - lesions of differing age side-by-side
LM DDx	asbestosis, chronic hypersensitivity pneumonitis, collagen vascular disease (e.g. systemic lupus erythematosus, rheumatoid arthritis, scleroderma), chronic drug toxicity
Stains	iron stain -ve
Gross	lower lobe & periperal predominant: fibrosis, peripheral cysts
Site	lung - see diffuse lung diseases
Signs	signs of right heart failure
Symptoms	shortness of breath
Prevalence	uncommon
Radiology	interstitial pattern, lower lobe predominant, peripheral cysts
Prognosis	usually poor, dependent on amount of fibrosis
Other	histologic correlate of idiopathic pulmonary fibrosis
Clin. DDx	asbestosis, chronic hypersensitivity pneumonitis, collagen vascular disease (history missing), chronic drug toxicity (history missing), idiopathic pulmonary fibrosis
Treatment	lung transplantation

Usual interstitial pneumonia, abbreviated UIP, is a relatively common pattern in diffuse lung diseases. Overall, it is an uncommon pathology.

Idiopathic pulmonary fibrosis (abbreviated IPF) redirects here.

General

• It is sometimes used incorrectly as a synonym for idiopathic pulmonary fibrosis. It is a histomorphologic pattern and has a DDx (see below).
• UIP cannot be diagnosed via bronchoscopic or transbronchial biopsy, as it is peripheral.

Epidemiology

• Disease of the old - rare in under 50 years old.
• Dismal prognosis - mean survival after diagnosis ~ 2.8 years.

Radiology

• Honeycombing - multiple defects that obliterate the normal lung architecture - multiple spherical voids in the lung parenchyma; radiologically these are seen as lucencies.
  • Usually subplural, i.e. peripheral lung.
  • Classically lower lobe predominant.
• Traction bronchiectasis.

Note:

• Cysts - have thin walls (think of emphysema, lymphangioleiomyomatosis et cetera).
  • Cysts may be isolated/not close to a neighbour.
  • Medcyclopaedia defines it as: thin-walled, well-demarcated and >1 cm.

Microscopic

Features:

• Fibroblast foci:
  • "Crescent-shaped bulge" of fibroblasts -- a rounded projection of spindle cells into the airspace.
  • Location: in the areas of transisition between active inflammation and old inflammation.
  • Note: Technically, fibroblast foci are composed of myofibroblasts.
• Interstitial inflammation.
• Microscopic honeycombing.
  • Typically peripheral - cysts lined by ciliated epithelium.
• Spatial heterogeneity - patchy lesional distribution (areas of abnormal and normal lung may appear beside one another).
• Temporal heterogeneity - lesions of differing age side-by-side.

Notes:

• Disease worse distant from large airways: lower lung field predominance, typically worse at periphery of lobule and lung.
• Heterogeneity of inflammation: airspace macrophages & inflammation minimal in honeycombed foci.

DDx of UIP:

• Idiopathic pulmonary fibrosis (UIP not otherwise specified).
• Asbestosis = UIP-like pattern + ferruginous bodies with asbestos fibers.
• Chronic hypersensitivity pneumonitis (AKA extrinsic allergic alveolitis) - classically centrilobular predominant +/- granulomas.
• Collagen vascular disease - includes systemic lupus erythematosus, rheumatoid arthritis, scleroderma.
• Chronic drug toxicity.

Images

• 

  UIP - honeycomb change in UIP - low mag. (WC)

• 

  UIP - fibrosis - low mag. (WC)

• 

  UIP - fibroblast focus - high mag. (WC)

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A. Lung, Right Lower Lobe, Wedge Biopsy:
	- Usual interstitial pneumonia, see comment and microscopic.

B. Lung, Right Middle Lobe, Wedge Biopsy:
	- Usual interstitial pneumonia, see comment and microscopic.

C. Lung, Right Upper Lobe, Wedge Biopsy:
	- Usual interstitial pneumonia, see comment and microscopic.

Comment:
There are no findings to specifically suggest hypersensitivity. Clinical and radiologic 
correlation is suggested.

Alternate

Right Lower Lobe of Lung, Wedge Resection:
     - Usual interstitial pneumonia (UIP) pattern (fibroblast foci, bronchiolization, 
       extensive fibroelastotic scarring and focal calcification/bone formation), see comment.

Comment:
UIP pattern may be idiopathic. It is also be seen in the context of collagen vascular diseases, hypersensitivity reactions, and drugs; these need to be considered in clinical context along with the imaging findings.

Micro

Sections show lung parenchyma with:
Fibrosis (severity; lobar location): present (moderate-to-severe; peripheral predominant).
Fibrosis - lung field predominance: lower lobe > middle lobe > upper lobe. 
Fibroblast foci: present.
Temporal heterogeneity: present.
Spatial heterogeneity: present.
Peripheral cyst formation: present.
Inflammation: present - patchy, lymphocyte predominant.
Granulomatous inflammation: absent.
Blood vessel changes: present, moderate-to-severe.
Airspace changes: mucous plugs. 

See also

• Diffuse lung diseases.