A268 A CASE OF SEVERE RIGHT UPPER QUADRANT PAIN SECONDARY TO AN IGG4 RELATED INFLAMMATORY PSEUDOTUMOUR INFILTRATING THE LIVER CAPSULE

IgG4 related disease has become an increasingly recognized entity over the past 15 years, with a variable presentation that can include autoimmune pancreatitis, sclerosing cholangitis, sclerosing sialadenitis, orbitopathy and retroperitoneal fibrosis amongst others. While the pathophysiology of IgG4 related disease is not fully understood, at least some degree of autoimmunity is suspected. Inflammatory pseudotumours are a rare benign lesion which primarily present in the lung, but up to 8% can be found in the liver. Rarely, these masses are associated with IgG4 related disease. A 59 year old male of Korean decent with a previously presumed diagnosis of IgG1 and 2 related autoimmune cholangitis and pancreatitis with secondary compensated cirrhosis was admitted to hospital due to a 1 month history of worsening right upper quadrant pain. Upon initial diagnosis 2.5 years prior, his total IgG was elevated at 34 with an IgG1 elevated at 20 and an IgG2 elevated at 10. His IgG4 was normal at 1, as was his IgG3. He was started on prednisone initially and maintained on azathioprine 100mg daily until his presentation to hospital, with a complete normalization of his total IgG and IgG subclasses. His anti-mitochondrial, anti-nuclear and anti-smooth muscles antibodies were also negative. On this presentation, a CT of the abdomen, followed by an MRI, revealed a 2.8 X 2.5cm mass in segment 5 of the liver, which extended into the capsule. Note was made of growth from a size of 2cm on an MRI from 8 months prior, on which the lesion was thought to be a perfusion abnormality. Liver enzymes and function tests were normal, as were the total IgG and IgG subclasses. A contrast enhanced ultrasound (CEUS) was completed with features concerning for malignacy (figure 1). A percutaneous biopsy of the lesion guided by CEUS demonstrated a lymphoplasmacytic predominant mass with up to 70 IgG4 plasma cells per high power field and a ratio of IgG4 to IgG of 45%. A diagnosis of an IgG4 related inflammatory pseudotumour was established. The patient was kept on azathioprine and prednisone was initiated at 40mg per day with a plan to taper by 5mg weekly until therapy was complete. Two weeks after the initiation of prednisone, the patient’s pain had resolved and on repeat CEUS, it had become less mass-like and had shrunken slightly. While IgG4 inflammatory pseudotumours of the liver are rare, they must be considered in the differential diagnosis of a hepatic mass, even in the setting of normal IgG4 levels and apparently stable autoimmune disease on azathioprine. In this case, the pseudotumour invaded into the liver capsule, and was cause for significant pain. Along with biopsy, CEUS was a helpful adjunct in establishing the diagnosis. Prednisone was an effective therapy for this patient. Figure 1. 59 year old male with presumed IgG1 and IgG2 autoimmune cholangitis and pancreatitis presented with acute onset of right upper quadrant pain. Gray scale ultrasound revealed a segment 5 heterogeneous mass in the liver abutting the capsule. This very unusual liver mass is superficial and appears complex with apparent small cystic black holes. The mass had rapid washout with contrast enhancement concerning for malignancy and prompted a liver biopsy. Histology was consistent with an IgG4 inflammatory pseudotumour. None

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