7292 Central AVP Deficiency in Erdheim-Chester Disease in the Era of Molecular Diagnostics

Abstract Disclosure: J. Hewlett: None. S. Mohan: None. C.J. Davidge-Pitts: None. J. Abeykoon: None. R. Go: None. D.Z. Erickson: None. Objective: Erdheim-Chester Disease (ECD) is a multisystem histiocytic disorder which can infiltrate the pituitary gland, often leading to endocrine dysfunction. Central Arginine Vasopressin Deficiency (cAVP-D) commonly affects ECD patients, and those harboring BRAFV600E are reported to have an increased risk. Insufficient data exist about the risk associated with other mutations, and if cAVP-D or pituitary imaging improves with targeted therapies (TT). Methods: We conducted a review of a prospectively maintained database of adults with ECD treated at a tertiary center between 1992-2023. Objectives of this study were to identify mutations associated with cAVP-D and assess for improvement in cAVP-D (remission of disease or decrease in dose of desmopressin) or pituitary gland involvement (via MRI imaging) following TT for ECD. Results: Of 148 patients with ECD, the majority were male (98, 66.2%) and the mean age at diagnosis was 56.5 years [range: 19-82]. Median length of follow-up was 24 months (95% CI, 17 to 27). Of 121 (81.8%) patients with molecular testing results, 89 (73.6%) harbored a somatic mutation. 67 of 89 (75.3%) carried BRAF mutations, with BRAFV600E in 61 (91.0%) and missense mutations/fusions in 6 (9.0%). 22 of 89 (24.7%) patients harbored other somatic mutations, with MAP2K1 in 13 (14.6%) being the most common. 35 (23.6%) patients were diagnosed with cAVP-D, and the median onset of polyuria and polydipsia prior to diagnosis of ECD was 51 months (95% CI, -120 to -6). Molecular testing was performed in 28 patients with cAVP-D: 17 (60.7%) harbored BRAF mutation and 3 (10.7%) MAP2K1 mutation. There was no significant association between the presence of cAVP-D and MAP2K1 (p=0.69, 95% CI, -0.08 to 0.21). The association between cAVP-D and BRAF did not reach statistical significance (p=0.07, 95%CI, -0.03 to 0.38). Additionally, there was no association between BRAF and timing of cAVP-D symptoms before ECD diagnosis (p=0.08, 95% CI -163.4 to 10.3). Pituitary MRI was available in 32 patients with cAVP-D (91.4%) showing infundibular involvement in 17 (53.1%) and loss of the posterior bright spot in 5 (15.6%). 28 (80%) patients with cAVP-D received systemic therapy, 18 (64.3%) of whom received TT. One patient with cAVP-D was able to discontinue desmopressin. Improvement of pituitary MRI was noted in 7 (21.9%), among whom 4 received TT, 2 received systemic non-TT, and 1 was lost to follow-up. There was no significant MRI improvement associated with TT (p=0.67, 95% CI -0.30 to 0.42). Conclusion: In this large cohort of patients with ECD, of whom the majority underwent molecular testing, we identified no association between MAP2K1 mutation and cAVP-D, and no impact of TT on the clinical course or MRI findings associated with cAVP-D. BRAF mutation carriers were more likely to have cAVP-D and more likely to have onset of symptoms closer to ECD diagnosis, but the results did not reach statistical significance. Presentation: 6/2/2024