SUN-524 Patient with Pseudohypoparathyroidism Type 1B, Graves Disease, and False Positive HIV Screen- a Rare Presentation

Background: Pseudohypoparathyroidism 1B (PHP1B) is a disorder that can lead to thyroid stimulating hormone (TSH) resistance and hypothyroidism, although it is rarely associated with thyrotoxicosis. Clinical Case: A 25-year-old female with a history of PHP1B, seizures due to hypocalcemia, and family history of PHP1B in her three sisters and brother presented to our emergency room with a fever of 103(0)F and generalized malaise. Two months prior, she was seen at an outside hospital with palpitations and bulging of the left eye. There, she was diagnosed with hyperthyroidism, started on methimazole, and asked to continue levetiracetam and calcitriol upon discharge. On our exam, she had tachycardia of 120 beats per minute, left eye proptosis, positive Chvostek sign, and a large goiter with bruit. Reflexes were 3+. Laboratory evaluation revealed corrected serum calcium of 6.1 (8.5-10.5 mg/dL), TSH < 0.01 (0.34-5.60 mU/L), free T4 2.81 (0.60-1.60 ng/dL), free T3 13.0 (2.4-4.2 ng/dL), and iPTH 131 (12-88 pg/mL). ELISA testing for screening of HIV was positive. She was treated with IV calcium gluconate, methimazole, propranolol, and hydrocortisone. Her home doses of calcitriol and calcium were resumed. She was referred for total thyroidectomy as an outpatient once she became euthyroid. The confirmatory Western blot test for HIV was negative. It was determined that presence of thyroid stimulating immunoglobulin resulted in the false positive ELISA test. Discussion: Hyperthyroidism with Graves disease seen in PHP has only very rarely been reported. (1) It has been postulated that abnormal electrolytes and elevated parathyroid hormone from PHP may lead to stimulation of the thyroid gland and perpetuate Graves disease symptoms. (2) Furthermore, the presentation of thyrotoxicosis despite TSH resistance in PHP indicates that there may be other mechanisms for TSH receptor antibodies to take effect in these patients which have not yet been determined. (3) Lastly, autoimmune diseases, including Graves disease, can cause a false-positive HIV ELISA as seen in our patient. Conclusion: Although rare, thyrotoxicosis may present in patients with PHP1B. Additionally, it should be kept in mind that autoimmune diseases such as Graves disease can cause a false positive HIV ELISA, and follow-up Western blot testing should therefore be performed. References: (1) Gerhardt A, Hackenberg K. 2002. Pseudohypoparathyroidism and Graves’ disease: a rare combination of two endocrinological diseases. Exp Clin Endocrinol Diabetes. 110:245-247 (2) Morón-Díaz et al. 2019. A rare case of Graves’ disease in a patient with type 1B pseudohypoparathyroidism and associated TSH resistance. Endocrine Abstracts. 63:96 (3) Richard Prokesch. 2010. Navigating False Positive Testing. HIV Specialist (AAHIVS). 2:27