6462 A Case of Presumed IgG4 Related Hypopituitarism

Abstract Disclosure: W. Lai: None. A. Turtz: None. P. Traisak: None. F.H. Morgan: None. Introduction: Hypopituitarism is a rare disorder of decreased hormone secretion with a prevalence of 0.05% [1]. It is exceedingly rare to be caused by pituitary inflammation such as IgG4 mediated plasmacytic cell invasion hypophysitis which accounts for 4% of all hypopituitarism cases [2]. We present a challenging case of presumed IgG4 hypophysitis using Leporti criteria. Case: A 79 year old male with a medical history of hypertension, hypothyroidism, and mitral valve repair presented to the hospital for syncope, fatigue, and hypotension. Blood work done was significant for a low cortisol of 0.8 µg/dL (5-25 µg/dL), ACTH of 5 pg/mL (10-60 pg/mL), TSH of 0.120IU/mL (0.5-5IU/mL), and FT4 of 0.89ng/dL(0.7-1.9ng/dL). Prolactin and IGF1 were unremarkable. He was started on hydrocortisone 10 mg in the morning and 5 mg in the evening with improvement in symptoms. On follow up with Endocrinology, an MRI revealed an intrasellar/ suprasellar mass measuring 18 mm craniocaudal, sellar component of 11x9 mm, and suprasellar component 13x9mm with effacement and superior displacement of the optic chiasm raising the question of hypophysitis, and an incidental finding of a parotid mass. IgG4 testing was sent with results elevated at 377 mg/dL. PET scan showed uptake in the pituitary gland, right parotid gland, as well as mediastinal and hilar lymphadenopathy. Biopsy of the right parotid lesion showed pleomorphic adenoma. Patient deferred biopsy of hilar lymph nodes.The patient’s steroids were changed to prednisone to treat likely IgG4 mediated hypophysitis and repeat MRI after 4 weeks of treatment showed a reduction in the size of the pituitary lesion. He was subsequently referred to rheumatology for further evaluation of systemic disease. Additional work up including SPEP, Cryoglobulins, ANA IFA, ANCA, C3, C4, SSA, SSB, ACE, and immunoglobulin levels were negative. Conclusion: IgG4 related hypopituitarism is a rare diagnosis that is difficult to diagnose. In this case a definitive diagnosis with histological sampling was not obtained but a working diagnosis of IgG4 related hypophysitis was made based on clinical presentation, MRI findings, an elevated IgG4 > 140, and response to treatment. He ultimately fulfilled the diagnostic criteria proposed from Leporti et al [3]: MRI with sellar mass, IgG4 > 140mg, and steroid responsive decrease in size of the pituitary lesion, with concomitant improvement of symptoms. This case highlights the difficulty in diagnosis of IgG4 hypophysitis and the benefit of using non histological diagnostic criteria. Presentation: 6/1/2024