Case Presentation: Case presentation:A 56 year-old caucasian man with no significant past medical history presented to our center with acute left upper quadrant abdominal pain. CT angiography of the thorax was performed to rule-out pulmonary embolism which showed thickening and enhancement of the splenic and hepatic arteries without aneurysmal dilatation. To evaluate this further, a dedicated CT angiogram of the abdomen was performed, suggestive of splenic infarct. Serologic evaluation was negative for antinuclear antibody (ANA), cytoplasmic and perinuclear ANCA (cANCA, pANCA), anti-phospholipid antibodies and revealed normal ESR, CRP, C3, C4, complement levels and IgG4. Hepatitis B and C serologies were negative. On the fifth day of hospitalization, our patient developed severe left flank pain and an erythematous papular rash in the left groin. MRI and MRA of the kidneys revealed left renal infarction and biopsy of the rash revealed spongiotic interface dermatosis, without evidence of vasculitis. Treatment with high dose steroid was initiated with improvement in symptoms. Repeat CT angiography of abdomen showed significant mural thickening and luminal narrowing of the celiac axis and its branches with small pseudo-aneurysms along the celiac trunk, confirming the diagnosis of PAN.

Discussion: Polyarteritis nodosa (PAN) is a rare systemic necrotizing vasculitis affecting 2-33 persons per million. Most cases of PAN are idiopathic, however Hepatitis B and C infections and hairy cell leukemia can be the trigger in some cases. PAN typically affects medium-sized arteries and can affect different organs in various combinations, including skin, muscle, joints, kidneys, heart, nervous system and gastrointestinal tract. Laboratory testing usually reveals a prominent nonspecific acute phase response and anti-neutrophil cytoplasmic antibody (ANCA) is typically negative. Diagnosis is based on biopsy and pathologic confirmation of vasculitis in medium-sized arteries of symptomatic organs. When biopsy is not feasible or negative, visceral angiography revealing multiple microaneurysms can support the diagnosis.
Here we describe a rare case of PAN with negative inflammatory markers and localized gastrointestinal involvement.

Conclusions: We report a rare and challenging case of PAN. Despite negative inflammatory markers and skin biopsy, our patient developed vasculitis associated infarction of abdominal organs. In PAN vasculitis, arterial narrowing in the setting of vessel wall inflammation and intimal proliferation can reduce blood flow and predispose to thrombus formation in the involved organs, resulting in ischemia or infarction. Diagnosis was confirmed on repeat CT angiography of the abdomen showing small pseudo-aneurysms along the celiac trunk. Our patient responded appropriately to high dose steroids. This case demonstrates the challenges in making the diagnosis of PAN in a patient presenting with normal inflammatory markers and atypical vasculitis with limited organ involvement.