These acronyms refer to definitions of interstitial lung disease where fibrosis (scarring) of the lungs becomes worse over time.

Unfortunately, in the field of ILD there are many such acronyms which can be quite confusing. These two terms refer mostly to technical definitions according to relevant clinical trials or international guidelines in the field.

In brief,

PF-ILD stands for progressive fibrosing interstitial lung disease

PPF stands for progressive pulmonary fibrosis

It is difficult to consider these as specific diagnoses as they can represent an umbrella term covering several other ILD diagnoses. Progressive, worsening lung fibrosis has important clinical implications regardless of the cause. In some cases, patients may be eligible for antifibrotic medication aimed at slowing down the scarring process if they meet the PF-ILD or PPF criteria.

Do not worry if these acronyms are confusing – your doctor may be able to clarify what they mean in your case.

Some more clarification regarding the definitions can be found below:

PF-ILD

This definition is based on a major clinical trial performed in patients who suffered with progressive forms of fibrotic interstitial lung diseases and were treated with an antifibrotic called nintedanib (the INBUILD trial).

The definition is based on the trial inclusion criteria and includes patients who despite standard treatments still progressed (within 2 years). Progression was defined based on a combination of respiratory symptom worsening, decline in lung function parameters (on spirometry) and radiological worsening (on chest CT scanning). One of the following three criteria had to be met for inclusion (within 2 years):

1. A drop in a lung function parameter called forced vital capacity (FVC) by more than 10% of the predicted value
2. A drop in FVC between 5 to 10%, but also worsening respiratory symptoms or increased fibrosis on chest CT scanning.
3. Worsening respiratory symptoms and also increased fibrosis on chest HRCT

PPF

The progressive pulmonary fibrosis (PPF) definition is based on the most recent professional guideline in place at the time of writing this article.

To meet the PPF definition, two of the following criteria need to be met within the last year without an alternative explanation:

1. Worsening respiratory symptoms
2. Lung function decline, measured as an absolute decline in a parameter called forced vital capacity (FVC) of more than 5% of the predicted value, or an absolute decline in another lung function parameter called TLCO of more than 10%
3. Radiological progression of the fibrosis on chest CT scanning

Why are the definitions important?

In many parts of the world, the PF-ILD and PPF definitions are used to determine which patients may be eligible for the antifibrotic drug nintedanib. They are functional definitions which help decision-making in clinical practice. Patients who do not meet the criteria are unlikely to benefit from adding nintedanib to standard treatments – however this may be subject to change in the future depending on research data. The medication may also not be reimbursed if the criteria are not met.

I strongly encourage you to check with your doctor for updated information in your case, as the field of ILD evolves rapidly.