7588 Coexistent Toxic Nodular Goiter And Primary Hyperparathyroidism (PHPT), A Combo With Diagnostic And Management Implications

Abstract Disclosure: D. Dave: None. A. Bhan: None. S.D. Rao: None. About 17-84% of patients with PHPT have concomitant thyroid disorders, but the prevalence of coexistent hyperthyroidism in PHPT varies 9-14 %. A vast majority had Graves’ disease with only 3 cases of toxic multinodular goiter (MNG) and PHPT reported in the literature as of 2022 ([1]). We present a rare case of coexistent toxic MNG and PHPT. Case Description: A 68y woman presented with recent 23 kg unintended weight loss and palpitations, but no other symptoms. Denied having kidney stones or fractures. On examination she had fine tremors of hands, MNG without exophthalmos. An ultrasound showed multinodular MNG with cystic lesions. A diagnosis of toxic MNG was made. Laboratory results were: TSH (<0.01 uIU/mL), free T4 1,68 ng/dL (normal: 0.61-1.44 ng/ml), high serum Ca (11.0 - 11.4 mg/dl) over 4y, but PTH was unavailable prior to the visit when it was 107 pg/ml and 89 pg/ml after 3 months of antithyroid therapy. Despite clinical and biochemical euthyroidism after 3 months, serum Ca and PTH levels remained high (11.4 mg/dl and 89 pg/ml respectively). Because she had pulmonary embolism a few years ago, we deferred parathyroidectomy until complete remission of hyperthyroidism. Discussion: Hypercalcemia is the biochemical hallmark of PHPT but can occur in 2-10% of patients with hyperthyroidism alone but only 1% of those will have coexistent PHPT. When these two conditions coexist, hypercalcemia is moderate to severe, and an occasional patient may present with hypercalcemic crisis (2). Prior to the availability of PTH assays, it was a challenge to diagnose coexistent PHPT. Hypercalcemia in hyperthyroidism responds to propranolol but not in PHPT, although the response is variable (3). With the availability of sensitive PTH assays, this maneuver is not necessary. In most cases, current PTH assays distinguish hypercalcemia of hyperthyroidism with suppressed PTH from coexistent PHPT in whom PTH level is non-suppressed or elevated. Monitoring serum Ca and PTH levels during therapy of hyperthyroidism would be useful as normalization of serum Ca and PTH has occasionally been reported (4). In our patient, serum Ca and PTH levels remained high with 3-months of methimazole and atenolol. The impact of both conditions on bone and mineral metabolism are profound, with fractures and kidney stones. Since kidney stones are uncommon in hyperthyroidism, presence of kidney stone in a hyperthyroid hypercalcemic patient should alert the possibility of PHPT. Similarly, significant decrease in bone density in such patient also raises the possibility of PHPT. Prompt diagnosis and appropriate treatment of both conditions is necessary to avoid irreversible complications. References:1.Zhang W, et al. BMC Endocr Disord. Aug 9 2022;22(1):200.2.Baldane S, et al. Endocrine regulations. Oct 1 2016;50(4):225-8.3.Luong KV, et al. Endocr Pract. Jul-Aug 1996;2(4):250-4.4.Barsotti MM, et al. Arch Intern Med. Jun 1979;139(6):661-3. Presentation: 6/3/2024