NOTES FROM AN ARTICLE:
Differential diagnosis of usual interstitial pneumonia (UIP): When is it truly idiopathic?
PUBLISHED IN EUR RESPIR REV: 14; 23: 308-319
Wim A. Wuyts and al
(with the permission of the author)
In a recent case-cohort study, almost half of patients initially diagnosis with IPF based on the 2011 criteria, were subsequently diagnosis with chronic HP following elicitation of a detailed history etc….
Differentiating between the two has a substantial therapeutic and prognosis implications :
Indeed, immune suppressive therapy which is often appropriate in chronic HP (together with removal of offending Antigen if identified), has been associated with increased risk of death in patients with IPF.
IPF AND CHRONIC HP CAN BE INDISTINGUISHABLE :
In chronic HP , history is of paramount importance :
- History of exposure to avian antigen,, BAL lymphocynosis, serum precipitin….
- Radio (ground-glass opacities, poorly defined centrilolular nodules, mosaïc attenuation, air trapping, and lack of lower zone predominance on HRCT).
- Histopathologic finding suggestion of chronic HP :
- Bronchiolocentric accentuation of the inflammation,
- Perbronchial fibrosis,
- Bronchial epithelial hyperplania,
- And presence of granuloma / or multinucleated giant cells.
IPF after exclusion of other pathologies Secondary to :
- Rhumatoïd arthists +++
- Sjogren disease
Interstitial lung abnormalities can be presenting feature in almost 10 – 20 % of cases
UIP is defined on CT as a peripheral and basal distribution of honeycomb changes with traction bronchiectasis ; irregular interlolular septal thickening and minimal ground-glass opacity. When all these features are present, the Dg accuracy of CT approaches 90 – 100 %, with honeycombing being the strongest predictor of Dg of UIP.
However, the abnormalities are only seen in around half of all patients with IPF.
The histology of UIP pattern :
1 - Spatial heterogeneity with patchy parenchymal involvement
2 - Architectural distorsion
3 - Temporal heterogeneity (fibroblastic foci)
The histology of “secondary” UIP can be identical to “idiopathic” UIP/IPF
Importance of clinical and/or laboratory findings. +++
Sjogrën disease : pattern UIP (++)
Rhumatoid arthritis: pattern NSIP (+)
- Follicular bronchiolitis with germinal centers or preominent interstitial lymphoid infiltrate in a background of fibrotic lung with a UIP pattern.
- Overlapping acute, subacute and chronic changes in the same biopsy when CTD produces pulmonary fibrosis.
Patients with CTD-UIP, have fewer fibroblastic foci, smaller honeycomb cysts and less emphysema than patients with IPF.
Pleural fibrosis is typically present in rheumatoid arthritis and other CTDs with thoracic manifestations but is uncommon in IPF.
- Most cases of chronic HP are characterized by AIRWAY CENTERED FIBROSIS
- Occasionally fibrosis indistinguishable from the UIP pattern observed in IPF.
- Histopathological features suggestive of chronic HP as the etiology are :
1 - Upper-lobe predominant UIP pattern.
2 - Presence of “Bridging fibrosis” i,e, linear connection between centrilobular and perilobular areas (subpleural and/or paraseptal), or between centrilobular and adjacent centrilobular areas.
3 - Presence of interstitial (not intra-alveolar) isolated giant cells or granulomas.
4 - Cellular bronchiolitis with bronchiolocentric damage and peribronchiolar metaplasia (so called lambertosis).
These abnormalties are subtle, requiring a meticulous examination of serial sections.
AMiODARONE PULMONARY TOXICITY
Acute or subacute alveolar injury with hyperplastic type 2 pneumocytes.
Intraalveolar foamy macrophages.
BOOP and DAD may be observed.
Type 2 pneumocytes have a peculiar foamy cytoplasm.
Typical BAL profile in IPF:
- Moderately neurophils (10 – 30 % of the total cells) .
with or without PN eosinophils