IgG4-Related Retroperitoneal Fibrosis in a Patient With B-Cell Lymphoproliferative Disorder.

We report an interesting case of a 25-year-old male patient who presented with a complaint of pain in the abdomen for six months, which was not associated with any other symptom, the patient was diagnosed with IgG4-related retroperitoneal fibrosis (RF) via endoscopic ultrasound (EUS)-guided biopsy. He was prescribed steroids and proton pump inhibitors. Due to the limited presentation and rarity of RF, diagnosis of this disease requires extensive diligence and care. In this case report, we underscore the importance of considering the differential diagnosis of RF or Ormond's disease when a patient presents with vague symptoms of pain in the abdomen. According to our knowledge, this is the first case of IgG4-related RF in a patient with B-cell lymphoproliferative disorder reported from Pakistan.