When to test for myositis antibodies in usual interstitial pneumonia on chest CT?

Usual interstitial pneumonia (UIP) is a key pattern of interstitial lung disease (ILD), most commonly linked to idiopathic pulmonary fibrosis (IPF). Identifying underlying autoimmune conditions such as myositis is clinically relevant, yet guidelines provide limited recommendations regarding myositis antibody (MSA) screening.

We retrospectively analyzed patients with UIP who underwent systematic MSA screening at our center. Clinical and serological characteristics were compared between MSA-positive (MSA+) and MSA-negative (MSA-) groups. Logistic regression was used to identify predictive factors.

Among 134 patients, 15 (11 %) were MSA+. Compared with MSA- patients, MSA+ cases were more likely to present with autoimmune disease (p = 0.03), ANA ≥ 1:320 (p < 0.001), and positive rheumatoid factor (p = 0.04). A four-parameter profile combining ANA < 1:320, absence of rheumatoid factor, no hypergammaglobulinemia, and no Raynaud's phenomenon strongly predicted MSA negativity with excellent specificity (100 %), modest sensitivity (35 %), and good overall discriminative ability (AUC = 0.82).

In patients with UIP, a simple four-parameter profile (ANA < 1:320, absence of rheumatoid factor, absence of hypergammaglobulinemia, and absence of Raynaud's phenomenon) strongly predicts negative MSA status. These findings support a more targeted approach to MSA screening, potentially improving diagnostic accuracy, guiding treatment decisions, and reducing unnecessary testing in UIP.