Can Desquamative Interstitial Pneumonitis (DIP) present with a Usual Interstitial Pneumonia (UIP) pattern?

Can Desquamative Interstitial Pneumonitis Present with a UIP Pattern?

Yes, desquamative interstitial pneumonia (DIP) can be associated with a radiological and/or pathological pattern compatible with usual interstitial pneumonia (UIP), though this is not the typical presentation of DIP. 1

Radiological Features of DIP vs. UIP

Typical DIP Radiological Findings

• Ground-glass opacities with bilateral, lower lobe predominance (92% of cases) 2
• Relatively well-preserved lung architecture in most cases 3
• Small cystic spaces that may be stable, regress, or occasionally increase over time 3
• Peripheral distribution of abnormalities in approximately 59% of cases 4

Distinguishing Features from UIP

• DIP typically shows more extensive ground-glass opacities compared to UIP 4
• DIP usually has fewer cystic changes/honeycombing than classic UIP 4
• Traction bronchiectasis is uncommon in DIP (reported in only 1 of 8 patients in one study) 3
• Architectural distortion is less common in DIP than in UIP 3

Diagnostic Challenges

Overlap with UIP

• DIP can be associated with a radiological and/or pathological pattern compatible with UIP, making differentiation challenging in some cases 1
• The French Practical Guidelines specifically note that DIP may be associated with a UIP pattern, complicating the diagnostic process 1

Distinguishing Features on HRCT

• According to HRCT criteria for UIP pattern, extensive ground-glass abnormalities (when extent exceeds reticular abnormality) are considered inconsistent with UIP pattern 1
• Since DIP typically presents with predominant ground-glass opacities, this feature helps distinguish it from classic UIP 4

Clinical Context and Differential Diagnosis

Smoking Association

• 81% of DIP patients have a history of smoking 2
• DIP is often categorized as a smoking-related interstitial lung disease 1
• Unlike IPF (which presents with UIP pattern), DIP often responds, at least partially, to smoking cessation 5

Other Considerations

• DIP may be the first clinical manifestation of a connective tissue disease 1
• 22% of DIP patients have occupational exposures that may contribute to disease 2
• Bronchoalveolar lavage (BAL) can help distinguish DIP from IPF, as an increased number of lymphocytes (>30%) does not favor IPF 1

Disease Progression and Relationship to UIP

Natural History

• Short-term follow-up studies suggest that DIP does not typically progress to UIP 3
• However, DIP can behave as a progressive disease more often than generally thought 2
• Some patients with DIP develop progressive irreversible fibrosis despite treatment 6

Treatment Response

• DIP generally shows better response to corticosteroids than IPF with UIP pattern 5
• Despite treatment, persistent abnormalities can be seen on pulmonary function testing and radiologic studies 5
• Progressive disease with eventual death can occur in subjects with DIP, especially with continued cigarette smoking 5

Diagnostic Approach

Multidisciplinary Discussion

• When radiological patterns are mixed or atypical, multidisciplinary discussion is essential to determine the clinical significance of individual patterns 1
• The 2022 ATS/ERS/JRS/ALAT guidelines emphasize the importance of integrating clinical, radiological, and when available, pathological findings 1

Biopsy Considerations

• Surgical lung biopsy is typically required for definitive diagnosis of DIP 5
• Transbronchial biopsies are often nondiagnostic in DIP 5
• Histologically, DIP shows accumulation of macrophages in alveolar spaces with interstitial inflammation and/or fibrosis 6

In summary, while DIP can occasionally present with features that overlap with UIP pattern, the predominance of ground-glass opacities, relative paucity of honeycombing, and better preservation of lung architecture in DIP typically allow differentiation from classic UIP in most cases.