Immunoglobulin-G4 Related Disease: A Rare Entity with Many Clinical Faces - Literature Review and Case Illustration.

Introduction: Immunoglobulin-G4 Related Disease (IgG4-RD) is a group of multi-system, fibro-inflammatory conditions characterised by elevated IgG4 levels and unique histopathological features. Clinical presentations of the disease are highly variable, albeit there exist distinct phenotypes in the presentations of the disease. IgG4-RD is a differential diagnosis that should be missed in any case of chronic inflammatory and tumefactive pathology. Case Discussion: We present the case of a 47-year-old diabetic female who presented with features suggestive of acute pyelonephritis. On further evaluation, our findings unmasked a rare constellation of pancreatitis, orbital pseudotumor, and venous thrombosis. After an astute clinical observation by our team, we were able to decipher these as features of distinct phenotypes under the IgG4-RD spectrum with minimal overlap (pancreato-hepatobiliary disease, head and neck disease, and retroperitoneal disease groups, respectively). Literature Review: We have presented an extensive review of the recent literature pertaining to the etiopathogenesis, clinical features, diagnostic protocol and management consensus for IgG4-related disease. A detailed account of the possible clinical presentations and work-up strategy for suspected patients has been emphasised in particular. Conclusion: IgG4-RD is diverse clinico-pathological entity that warrants a high degree of clinical suspicion. Once identified, efforts must be made to screen all possible foci of disease activity characteristic to the disease, as a multi-focal disease presentation of IgG4-RD is not unlikely.