IgG4 related disease as a cause of isolated retroperitoneal fibrosis with no other organ involvement; Case report

INTRODUCTION AND IMPORTANCE: Retroperitoneal fibrosis (RPF) is a rare disease characterized by the replacement of normal tissue with fibrosis and inflammation. We present the case of a 40-years-old gentleman with RPF whose presenting complaints were bilateral flank pain and weight loss and was found to have IgG4 related disease. To the best of our knowledge, IgG4-related disease with isolated retroperitoneal involvement is a very rare occurrence. CASE PRESENTATION: The diagnosis of IgG4-Related retroperitoneal fibrosis was made based on clinical, radiological and histopathological criteria. Imaging revealed isolated retroperitoneal involvement and the patient was started on oral steroids with a good clinical response after ten days. Repeated imaging months later showed significant regression in the fibrosis. CLINICAL DISCUSSION: RPF can occur due to many etiologies and is categorized to idiopathic and secondary. Factors associated with secondary RPF include medications, autoimmune disease, malignancy and IgG4 related disease. Almost all the reported cases of IgG4 related disease had evidence of multifocal involvement such as the pancreas, aorta and kidneys. Our patient was diagnosed with isolated RPF due to IgG4 disease. He met all the suggested diagnostic criteria, was started on oral steroids and had an excellent clinical outcome. CONCLUSION: IgG4 related disease can present with isolated retroperitoneal fibrosis without involvement of other organ systems. The diagnosis should be based on specific criteria. Treatment with corticosteroids can lead to remission both clinically and radiographically.