SAT-817 - Beyond Calcium: Band Keratopathy in Normocalcemic Hyperparathyroidism

Background:
Band keratopathy is a known ocular complication in patients with primary hyperparathyroidism (HPT) and is thought to be mediated via hypercalcemia and disordered calcium–phosphate metabolism. Patients with normocalcemic hyperparathyroidism (NPHPT) can manifest similar skeletal and renal complications as in HPT, however, in NPHPT ocular complications remain poorly characterized.

Case:
A 70-year-old man with a history of prostate cancer s/p radiation, CKD, type 2 diabetes with retinopathy and schizoaffective disorder was evaluated for persistent HPT after developing band keratopathy, diagnosed in 2009. History was negative for nephrolithiasis, fragility fractures or symptoms of hypercalcemia. Ocular history was negative for inflammatory conditions or other corneal abnormalities. Biochemical evaluation showed elevated PTH levels (64.3-179.4 pg/mL), no hypercalcemia with corrected calcium levels of 8.6-9.2 ng/mL, normal 1,25-dihydroxyvitamin D, and undetectable 24-hour urinary calcium. Vitamin D deficiency was excluded, and parathyroid localization studies were negative. DXA revealed osteopenia of bilateral hips with preserved bone density at distal radius. Initial elevation of PTH was identified in 2015. Patient received EDTA chelation for visually significant band keratopathy (left eye 2015 and right eye 2025).

Discussion:
Patients with NCHPT may develop complications like those seen in hypercalcemic HPT, including skeletal, renal, and metabolic manifestations. Band keratopathy is a recognized complication of HPT but has not been well described in NCHPT likely due to a lower calcium-phosphate product. The proposed mechanism involves corneal calcium (hydroxyapatite) deposition, which may occur despite normal serum calcium levels due to chronic PTH elevation and its effects on local calcium–phosphate metabolism. Altered PTH receptor signaling, end-organ resistance, or local ocular factors may contribute to corneal calcification in select patients with NPHPT. In this case, the patient had no other corneal abnormalities, or inflammatory conditions to account for band keratopathy.

Conclusion:
Patients with NCHPT demonstrate similar skeletal and renal complications to hypercalcemic disease and given that PTH levels (rather than calcium levels) correlate with some ocular changes, it is plausible that normocalcemic patients could develop similar ocular manifestations. No studies have systematically evaluated ocular complications specifically in the normocalcemic variant. This case highlights band keratopathy as a potential nontraditional manifestation of NCHPT, which may warrant an ophthalmology screening. Further investigation is needed to clarify implications for surveillance and management.

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