Anti-signal recognition particle-positive interstitial lung disease accompanied by metastatic duodenal adenocarcinoma: a case report

Abstract

Background: Anti-signal recognition particle (anti-SRP) antibodies are one of the two most commonly identified antibodies in immune-mediated necrotizing myopathies (IMNMs), a disease characterized by proximal muscular weakness. Anti-SRP-positive IMNMs predominantly affect middle-aged women; extra-muscular manifestations, such as interstitial lung disease (ILD), are not frequent and often mild. Malignancy is not a major concern for patients with IMNMs, especially those who are anti-SRP-positive. Case presentation: We present the case of a 64-year-old male who tested positive for anti-SRP antibodies and presented with ILDinstead of myopathy. This was accompanied by metastatic duodenal adenocarcinoma, and the patient experienced rapidly progressive interstitial lung disease (RP-ILD) during anticancer therapy. We chose low-dose immunosuppressive therapy after surgical removal of the metastatic cancerous lesion. The patient exhibited a positive response, whose respiratory condition gradually improved throughout the 2-year follow-up period. But the primary lesion appeared two years later than the site of metastasis, and the patient developed extensive metastases finally. Conclusions: The rare form of ILD in this patient highlights the significance of cancer screening and surveillance in atypical anti-SRP-positive patients. Low-dose immunosuppressive therapy following anticancer therapy resulted in significant improvement in ILD, serving as a treatment reference for paraneoplastic RP-ILD.