8651 Parathyroiditis- An Unusual Autoimmune Mediated-Process Presenting as Primary Hyperparathyroidism

Abstract Disclosure: M. Abdel-Malek: None. K. Alexiadou: None. N. Chander: None. S. Damji: None. S. Mukhopadhyay: None. F. Palazzo: None. T. Tan: None. Background: Inflammatory processes of the parathyroid gland are rare, not widely reported in the literature nor fully understood.Clinical case: A 67-year-old female was referred to the Endocrine team with a diagnosis of primary hyperparathyroidism in the context of severe symptoms related to hypercalcaemia and a background of osteoporosis. There was no known family history of endocrinopathies or autoimmune disease. Despite Cinacalcet treatment, she had a significant hypercalcaemia with an adjusted Calcium level of 2.99 mmol/L (RR 2.20 to 2.60) and a high Parathyroid Hormone (PTH) level of up to 46.1 pmol/L (RR 1.6 to 7.2). Localisation studies in the form of a Sestamibi and ultrasound scan failed to locate a parathyroid adenoma.During a four-gland exploration procedure, she had two pathological glands in the right inferior and left superior positions. She therefore underwent a bilateral inferior parathyroidectomy with no intra or immediate post-operative complications. On removal of the two abnormal parathyroid glands, her PTH level dropped from its peak of 48.1pmol/L to 12.2 pmol/L. However, most remarkably, the outcome of her histology revealed morphological appearances of a chronic parathyroiditis.On post-surgery follow-up, her symptomology of fatigue, nausea, abdominal pain and bowel symptoms resolved in addition to reported improvement in energy level. Her adjusted Calcium remained in the range 1.88mmol/L to 2.32mmol/L with a normalised and appropriately reactive PTH level.Over a year later, she developed sudden onset alopecia as well as oncholysis. Her autoimmune serology was negative with no other endocrine biochemical disturbance observed suggestive of an autoimmune-mediated polyendocrine process.She later developed hypocalcaemia despite high-dose Adcal D3, replete Vitamin D status and detectable PTH level (3.7 to 5.0 pmol/L), requiring admission for intravenous Calcium infusion. She was diagnosed with a functional hypoparathyroidism and subsequently commenced on regular Alfacalcidol with good symptomatic response. Conclusion: This case illustrates how a chronic parathyroiditis can mimic a primary hyperparathyroidism, and the even more unusual late presentation of a functional hypoparathyroidism in this context. Presentation: 6/2/2024