PO:37:267 | Mimickers of polyarteritis nodosa: a case of segmental arteriolar mediolysis

Filippo Santoro¹, Caterina Vacchi², Giulia Cassone², Maria Grazia Malandra¹, Dilia Giuggioli^1|2 | ¹UOSD Reumatologia, Ospedale San Camillo De Lellis, Rieti; ²UOC Igiene e Sanità Pubblica, ASL Rieti; ³Direzione Sanitaria, ASL Rieti, Italy

Background. The diagnosis of medium-vessel vasculitis often requires a thorough differential diagnosis to exclude non-inflammatory vasculopathies. We describe a case of Segmental Arteriolar Mediolysis (SAM), a non-inflammatory arteriopathy that can mimic medium-vessel vasculitis.

Materials and Methods. A 54-year-old woman presented to the Emergency Department with acute abdominal pain radiating posteriorly. Laboratory tests showed CRP 21.7 mg/dl and ESR 106 mm/h. Abdominal CT angiography revealed dissection of the superior mesenteric artery and partial occlusion of the inferior mesenteric artery at the proximal and mid-distal segments. A positive urine culture for Klebsiella pneumoniae confirmed a urinary tract infection, treated with targeted antibiotics. A week later, a second abdominal CT angiography showed celiac trunk ectasia, circumferential thickening of the inferior mesenteric artery (reported by the radiologist to be suggestive of vasculitis, see Figure 1), and reduced caliber of the left hypogastric artery, with thrombotic appositions in the right internal mammary, inferior mesenteric, and segmental renal arteries. Further investigations revealed negative ANA and ANCA, equivocal lupus anticoagulant (not confirmed on repeat testing), and negative anticardiolipin and anti-beta2-glycoprotein antibodies. CRP measured approximately 10 days after antibiotic therapy was 0.9 mg/dL. Given the suspicion of medium-vessel vasculitis, high-dose corticosteroids were started, later combined with methotrexate. At the 4-month follow-up, methotrexate had been discontinued due to elevated liver enzymes, and the patient was on low-dose prednisone (5 mg/day). She was asymptomatic, with persistently normal inflammatory markers. The normalization of CRP before corticosteroid initiation, the absence of vascular lesions typical of polyarteritis nodosa, and full clinical and laboratory remission without maintenance therapy raised suspicion for SAM. A new abdominal CT angiography showed near-complete resolution of the circumferential thickening of the inferior mesenteric artery and full resolution of thrombotic appositions. After multidisciplinary discussion with radiologists and vascular surgeons, a diagnosis of SAM was confirmed.

Conclusions. Segmental dissections of the celiac, mesenteric, and/or renal arteries are the key distinguishing feature of SAM (figure 2). This rare condition typically affects individuals aged 40–60 years, with a slight male predominance, and carries a high mortality rate (up to 50%) in cases of aneurysmal rupture. There are no established guidelines for treatment or follow-up, but optimal blood pressure control is essential to prevent vascular complications. The differential diagnosis from vasculitic diseases is challenging and relies on radiological, clinical, and laboratory assessment [1,2]. Correct identification of SAM, excluding vasculitic processes, has major implications for prognosis, treatment, and follow-up.