Abstract
IgG4-related disease (IgG4-RD) is an immune-mediated fibro-inflammatory condition which can affect various organs including the pituitary gland. The true annual incidence of this condition remains widely unknown. In addition, it is unclear whether IgG4 antibodies are causative or the end result of a trigger. With no specific biomarkers available, the diagnosis of IgG4-related hypophysitis remains a challenge. Additionally, there is a wide differential diagnosis. We report a case of biopsy-proven IgG4-related hypophysitis in a young man with type 2 diabetes mellitus. Learning points: IgG4-related hypophysitis is part of a spectrum of IgG4-related diseases. Clinical manifestations result from anterior pituitary hormone deficiencies with or without diabetes insipidus, which can be temporary or permanent. A combination of clinical, radiological, serological and histological evidence with careful interpretation is required to make the diagnosis. Tissue biopsy remains the gold standard investigation. Disease monitoring and long-term management of this condition is a challenge as relapses occur frequently.