¹Turkiya Abdulla Al Mamari, ²Tariq Al-Araimi, ²Ahmed Al Kindi, ²Hisham Al Dhahab
¹Al Nahdha hospital, ²Royal Hospital

Background(s): IgG4-related disease (IgG4-RD) is a systemic fibroinflammatory condition mediated by the immune system. Recognizing and characterizing this complex disease early is crucial to prevent severe organ damage caused by advanced fibrosis. Thus, timely diagnosis and treatment are essential to mitigate its impact.

Method(s): A 44-year-old man with diabetes on insulin since 2016 and hypertension on triple therapy was operated on in 2020 for an epidermoid cyst. He presented in June 2021 with itching and diarrhea. Abnormal liver tests led to abdominal ultrasound and CT, showing an 11 mm dilated common bile duct (CBD) with suspected stones. Further MRCP at Royal Hospital Oman revealed a common hepatic duct (CHD) stricture, mild pancreatic atrophy, and kidney hypo-enhancement. Labs showed elevated ESR at 81 mm/h (upper limit < 25), alkaline phosphatase at 170 iU/L (upper limit < 116), serum IgG, IgG4 subclass at 4.5 (upper limit <0.87 g/L), creatinine at 113 umol/L (62-110), reduced eGFR at 74 ml/min/1.73m^2 (N >90), and severe exocrine pancreatic insufficiency with fecal elastase at 1.2 µg/g (<100 µg/g), proteinuria at an estimate of 0.51 g/L. A rheumatologist diagnosed IgG4-related disease (IgG4-RD) based on clinical, serological, and radiological findings. Repeat MRCP MRI showed mild intrahepatic biliary dilatation, CHD stricture, severe pancreatic atrophy, and kidney involvement indicative of IgG4-RD. The patient started Rituximab and steroids therapy.

Result(s): Follow up MRCP MRI was done after the second dose of Rituximab showed mild improvement while Biochemical markers including IgG4 subclass level reduced to 0.81 g/L (upper limit <0.87 g/L), eGFR improved to 80 ml/min/1.73m2, creatinine improved to 103 umol/L, ESR normalized 17 mm/h, proteinuria was fluctuating 0.17 g/L -0.58 g/L. Maintenance therapy with Rituximab was recommended.

Conclusion(s): We reported a gentleman diagnosed with IgG4-related disease at the age of 44, contrasting with the reported age of diagnosis in large cohorts, which generally falls in the fifties to sixties range1. He exhibited uncommon hepatobiliary and pancreatic manifestations in MRCP MRI, including a non-obstructive stricture at the CHD, severe pancreatic atrophy, and progression of bilateral renal infiltrates 2,3 . Biochemically, he displayed evidence of pancreatic function loss, fluctuating ALP, fluctuating proteinuria, and mildly elevated creatinine. Notably, his complement levels were normal, although more than 50% of reported cases exhibit hypocomplementemia 2 . Despite the unavailability of a renal biopsy, we had sufficient evidence to initiate therapy. Our patient responded to treatment, as evidenced by a reduction in IgG4 levels and radiological improvement.

This case underscores the challenges in diagnosing and manging IgG4-RD. Further research is warranted to ascertain the optimal duration of Rituximab therapy and its indications, particularly in cases where biopsy is not available for therapy in IgG4-RD.