Although idiopathic pulmonary fibrosis (IPF) has a poor prognosis -- a median survival of only 3 years -- there is wide heterogeneity among individual patients. Some have a precipitous decline and die within months of diagnosis; others live for a decade or longer, with little apparent progression of IPF. This inherent uncertainty in prognosis provokes anxiety among patients and frustration among physicians trying to provide appropriate counseling, support, and timely referral to lung transplant centers. Previous outcome prediction models have been proposed, but so far none has been validated prospectively or entered wide use.
Brett Ley, Christopher Ryerson, Talmadge King, Harold Collard et al hope to change that. They have developed a new staging and outcome prediction system for IPF which they call the "GAP model" (for the Gender, Age, and Physiology variables it uses). After it showed good integrity in both its derivation and validation cohorts, they published their new GAP model, combined with a simple scoring system (the GAP index) in the May 15 Annals of Internal Medicine. (See also: Idiopathic Pulmonary Fibrosis Review - PulmCCM Central Topic Update.)
What They Did
Authors used the records of 228 patients with IPF at University of California-San Francisco as a derivation cohort, and 330 IPF patients from Morgagni-Pierantoni Hospital (Forli, Italy) and the Mayo Clinic as a validation cohort. Logistic regression was used to identify variables predictive of outcome, and a weighted point system was created to fit the data.
What They Found
The authors' GAP model / GAP index can be summarized as follows:
|GAP Index for IPF*|
|Physiology:||FVC 50-75% pred.||1|
|< 50% pred.||2|
|DLCO 36-55% pred.||1|
|< 36% pred.||2|
|Pt. cannot perform||3|
* Patient characteristics not fitting the described criteria are scored as zero.
|GAP Staging for IPF|
What It Means
Physicians may now have an effective tool to help predict the outcome of idiopathic pulmonary fibrosis; further validation in other cohorts could result in the GAP model entering wider use. Most physicians probably already had a sense that among patients with IPF, older patients with more severe impairments in lung function (forced vital capacity and diffusing capacity, or transfer factor) had a poorer prognosis than younger patients with less severe lung disease. Still, the data and the stratification of outcomes presented here could help doctors counsel patients more effectively, guide referral to lung transplant centers, and provide some low-risk patients with anxiety-reducing peace of mind.
Ley B et al. A Multidimensional Index and Staging System for Idiopathic Pulmonary Fibrosis. Ann Intern Med 2012;156:684-691.
See also: Idiopathic Pulmonary Fibrosis Review (PulmCCM Central Topic Update)