A Rare Presentation of Polyarteritis Nodosa (PAN)

Polyarteritis nodosa (PAN) is a connective tissue disease that affects arteries, causing necrotizing inflammation that can weaken the arterial walls, dilatation into aneurysms, and rupture in some cases. We present a case of a male with acute abdomen from aneurysmal rupture. The 48-year-old patient with a history of polysubstance use including cocaine and methamphetamines was admitted for acute hypoxic respiratory failure secondary to coronavirus disease 2019 (COVID-19) pneumonia and treated with broad-spectrum antibiotics and steroids. He also reported generalized abdominal pain and discomfort, and examination revealed abdominal distension that was diffusely tender on palpation, bowel sounds intact. Laboratory workup showed a progressive drop in hemoglobin requiring blood transfusions, no coagulopathy, anion gap metabolic acidosis, and lactic acidosis. Abdominal CT showed a 2 cm lobulated saccular aneurysm involving either the left gastric artery or splenic artery, associated with an extensive moderate amount of hemoperitoneum with hematomas (largest measuring up to 8.6 cm) abutting the gastric fundus and greater curvature of the stomach, which was likely secondary to aneurysmal rupture. Additionally, several other mesenteric vessels displayed some degree of dilation. Interventional radiology (IR)-guided splenic artery embolization for splenic artery aneurysm was done, after which his hemoglobin remained stable. The patient was given vaccine recommendations since splenic artery embolization would lead to asplenia. The aneurysms were attributed to either cocaine-related aneurysms or polyarteritis nodosa with visceral artery aneurysms. He denied rashes, oral ulcers, joint pain, subcutaneous nodules, blood in the urine, history of hepatitis or syphilis. Tertiary syphilis was ruled out after the Venereal Disease Research Laboratory (VDRL) test and rapid plasma reagin (RPR) test were negative. Complement C3 and C4 levels were normal. He was treated with high-dose IV methylprednisone after infection was ruled out. Due to the severity of PAN, therapy with IV cyclophosphamide therapy 15 mg/kg once every two weeks for three doses was initiated, followed by 15 mg/kg once every three weeks for three to six months (in combination with glucocorticoids prednisone 1 mg/kg body weight with slow taper). Cyclophosphamide was given with IV hydration and mesna. The presentation of PAN can vary widely. Most commonly, individuals experience symptoms such as fatigue, weight loss, fever, and chills. However, in rare cases, patients may present with isolated abdominal pain, similar to our patient. It's crucial to note that the rupture of an aneurysm can manifest as an acute abdominal issue, potentially leading to life-threatening situations. Immediate interventions to control bleeding are imperative in such cases. The treatment of PAN has a high success rate when a combination of cyclophosphamide and steroids is administered.