UIP diagnosed at surgical lung biopsy, 2000-2009: HRCT patterns and proposed classification system

High resolution CT (HRCT) is diagnostic of usual interstitial pneumonia (UIP) if honeycombing is present. However, biopsy-proven UIP also occurs in patients without honeycombing. Identification of specific HRCT patterns may enable specific diagnosis and allow more patients to enter clinical trials. Pattern may also predict prognosis. We sought to identify specific HRCT patterns in patients with biopsy-proven UIP (2000-2009) and to assess outcomes and serial change in pattern.

We reviewed the HRCT findings in 44 patients with biopsy-proven UIP and identified four distinct patterns: classic UIP (cUIP) with honeycombing, fibrosis without honeycombing (FnoH), minimal fibrosis (Fmin), and ground-glass present (GGOp). We reviewed electronic medical records for outcome information and serial HRCT examinations when available.

The extent of fibrosis varied between patterns; findings were always heterogeneous in the cUIP and FnoH patterns. Some Fmin patients had a more homogeneous appearance. The lower lobes were predominantly affected, but upper lobe abnormalities were always present. Mortality from respiratory failure and acute exacerbations occurred regardless of pattern. Serial progression from Fmin to FnoH to cUIP occurred, although in a variable manner. Some individuals had an acute illness (GGOp) as the initial manifestation of UIP.

The FnoH pattern may be diagnostic of UIP in the proper clinical setting; heterogeneity of HRCT appearance is critical and has not been previously emphasized. Grouping of patients on the basis of pattern may allow more accurate assessment of treatment effects. Further validation and study of these HRCT patterns is warranted. Histologic UIP predicts clinical course.