Molecular imaging and immune cell adhesion via vascular adhesion protein-1 in idiopathic inflammatory myopathy: a case report.

Dermatomyositis (DM) is an autoimmune disease characterised by muscle weakness, myalgia, and extramuscular manifestations and is classified as an idiopathic inflammatory myopathy (IIM). Imaging modalities are important for diagnosis and disease monitoring. Vascular adhesion protein-1 (VAP-1), an inflammation-specific adhesion molecule, may represent a promising target for disease assessment. Recently, the radiotracer [68Ga]Ga-DOTA-Siglec-9, which binds to VAP-1, was introduced for visualising vascular inflammation in giant cell arteritis. This case report aimed to generate preliminary insights into the pathophysiological involvement of VAP-1 and the possible diagnostic utility of [68Ga]Ga-DOTA-Siglec-9 positron emission tomography/computed tomography (PET/CT) in a patient with DM. A 59-year-old female patient with newly diagnosed, untreated DM was recruited. Demographic data, disease history, and laboratory parameters, including soluble VAP-1 (sVAP-1) levels, were collected. The patient underwent a [68Ga]Ga-DOTA-Siglec-9 PET/CT scan, followed by muscle biopsy of the vastus lateralis muscle. The patient's sVAP-1 level was 416.1 pg/mL, compared to 726.1 ± 126.7 pg/mL in controls (n = 8). The [68Ga]Ga-DOTA-Siglec-9 PET/CT scan demonstrated increased tracer uptake in the muscles of the shoulder girdle, back, forearm, and pharynx, consistent with clinical symptoms. Immunohistochemistry demonstrated endothelial VAP-1 expression in perimysial vessels along with DM-specific muscle alterations. In conclusion, we report the first application of [68Ga]Ga-DOTA-Siglec-9 PET/CT in a patient with IIM. While the findings support the feasibility of this imaging modality and provide preliminary evidence for the involvement of both soluble and endothelial-bound VAP-1 in immune cell trafficking and inflammation, any conclusions regarding its diagnostic or monitoring utility must remain cautious. Further studies with larger cohorts and longitudinal imaging are needed to evaluate [68Ga]Ga-DOTA-Siglec-9 PET/CT as a potential molecular biomarker for inflammation in IIM.