000 Desquamative Interstitial Pneumonia, DIP

What is it:
- Desquamative Interstitial Pneumonia (DIP) is a
  - rare,
  - smoking-related interstitial lung disease (ILD) characterized by:
    - The accumulation of
      - smoker’s macrophages (pigmented macrophages) in the alveoli.
    - Mild
      - interstitial inflammation and
      - fibrosis of the alveolar walls.
- Despite its name,
  - “desquamation”
    - does not involve epithelial cell shedding but
  - refers to the presence of
    - intra-alveolar macrophages.
Etymology:
- Derived from the Latin word desquamare (to scrape off or shed), which historically misrepresented the histological findings.
AKA:
- Smoking-related interstitial pneumonia, Alveolar macrophage pneumonitis.
What causes it:
- Primary cause:
  - Cigarette smoking is the most common and strongly associated cause.
- Other potential causes (rare):
  - Environmental exposures (e.g., dust, fumes).
  - Certain medications (e.g., chemotherapy agents).
  - Autoimmune diseases (rare).
What is the result:
- Chronic inflammation of the alveoli leads to:
  - Impaired gas exchange, and
  - Progressive pulmonary fibrosis in some cases.
- If untreated or if smoking continues, it may progress to fibrotic ILD.
How is it diagnosed:
- Clinical findings:
  - Gradual onset of symptoms, typically in middle-aged smokers.
  - Symptoms include:
    - Progressive dyspnea,
    - Chronic dry cough, and
    - Fatigue.
- Imaging studies:
  - Chest X-ray:
    - Diffuse reticular or ground-glass opacities, more pronounced in the lower lobes.
  - Chest CT:
    - Parts: Patchy ground-glass opacities with subpleural and basal predominance.
    - Size: Diffuse involvement of alveolar spaces, without discrete nodules.
    - Shape: Homogeneous or patchy.
    - Position: Predominantly lower lobes, peripheral or subpleural.
    - Character:
      - Absence of honeycombing (helps differentiate from UIP).
      - Mild interstitial thickening may be seen.
    - Time: Progressive without smoking cessation but reversible in early stages with treatment and lifestyle changes.
- Histopathology (gold standard):
  - Alveolar spaces filled with macrophages containing pigmented material (“smoker’s macrophages”).
  - Mild interstitial fibrosis and chronic inflammatory cell infiltrates.
- Exclusion of other diseases:
  - Rule out other smoking-related ILDs (e.g., respiratory bronchiolitis-associated ILD [RB-ILD], pulmonary Langerhans cell histiocytosis).
How is it treated:
- Smoking cessation:
  - The cornerstone of treatment. Most cases improve or stabilize if smoking is stopped.
- Corticosteroids (e.g., prednisone):
  - Effective in reducing inflammation in symptomatic cases or progressive disease.
- Immunosuppressive therapy:
  - May be considered in corticosteroid-refractory cases.
- Supportive care:
  - Pulmonary rehabilitation and oxygen therapy for advanced disease.
- Monitoring:
  - Serial pulmonary function tests (PFTs) and imaging to assess response and progression.
Radiological implications:
- DIP findings are reversible with early smoking cessation and corticosteroid treatment.
- Serial imaging is crucial to monitor resolution or progression to fibrosis.
- Absence of honeycombing distinguishes DIP from UIP.
Key points and pearls:
- Smoking-related ILD: DIP is almost exclusively found in smokers or individuals with significant smoking history.
- Ground-glass opacities: Lower lobe and peripheral distribution are hallmark features.
- Potential for reversibility: Early diagnosis and smoking cessation are critical to prevent progression.
- Differentiation: DIP must be distinguished from RB-ILD (which has more proximal airway involvement) and UIP (which shows honeycombing and more pronounced fibrosis).
- Histopathology clarity: Despite its name, “desquamation” refers to intra-alveolar macrophages, not epithelial cell shedding.

Position of Disease
Lower Lobe distribution
Ashley Davidoff MD TheCommonvein.net lungs-0771

Predominantly Lower Lobes Peripheral

Position of Disease
As the disease progresses the lower disease becomes more extensive and the disease progresses into the periphery of the upper lobes as well
Ashley Davidoff MD TheCommonvein.net lungs-0769c

aka alveolar macrophage pneumonia
a less angr brother to RB ILD

Inflammatory
- pigmented intra-alveolar macrophages and giant sells in the alveioli
Cause
- Mostly smokers
  - 10-40% are non smokers
    - inhalational toxic
    - druga
    - viral illness
    - autoimmune diseases
results
- Structural
  - Path
    - alveoli
      - architecture maintained
      - macrophages
        
        uniform diffuse
    - Interstitium
      - mild chronic inflammation
  - CXR
    - usually normal
  - CT
    - widespread
    - patchy ground glass
      - diffuse less common
    - lower lobes (70%)
      - bilateral
      - relatively symmetrical
      - peripheral (60%)
      - honeycomb can happen
- Functional
  - LFT mild impairment

Buzz

DIP
- aberrances
  - DIP imagine somebody dipping a rag of into cigarette smoke and dabbing it in the lower lung zones smoke

Lungs

Desquamative –
- squams = misnomer
- infiltrates represent alveolar filling with pigmented macrophages. alveoli

interstitial mucosa/submucosa vessels

pneumonia = “inflammation of the lungs,”

desquamate – fill the alveoli

Small Airways

Inflammation

Secondary Lobule

Alveoli

Inhalation – Lower Lobes

Smokers but

Desquamative Interstitial Pneumonia (DIP) is a rare form of idiopathic interstitial pneumonia (IIP).
Cause
- Smokers
  - also related to marijuana smoke inhalation,
- infections such as HIV,
- toxins, or
- occupational exposure (eg, to asbestos)
Results in
- infiltrates represent alveolar filling with pigmented macrophages. alveoli
Diagnosis
- Clinical
  - Cougn Dyspnea
  - DX difficult on
    - clinical and radiological features alone
    - requires a (surgical) lung biopsy
- Imaging
  - bilateral ground-glass opacities with
  - lower lobe predominance (92%).
  - irregular reticulation,
  - traction bronchiectasis and
  - cysts.
  - sometimes
    - ground-glass opacities
    - architectural distortion,
    - traction bronchiectasis and
    - honeycombing.
Path
- pigmented macrophages within
- most of the distal airspace of the lung
Histologically,
- DIP is similar to RB-ILD,
  - DIP and RB-ILD are a spectrum
  - differing in compartments involved
  - DIP not bronchiolocentric.
  - hyperplasia of the alveolar type II cells
  - distribution pattern more homogeneous a
  - mild peribronchial fibrosis