Occult Primary Hyperparathyroidism: A Case Report and Review of Parathyroid Ultrasonography

ABSTRACT Objective To discuss the diagnosis and management of occult primary hyperparathyroidism. Methods We present the biochemical and radiologic evaluation, treatment, and outcome of a woman with occult primary hyperparathyroidism which presented as an unusual neck mass on ultrasound. We also present a relevant literature review. Results A 52-year-old female presented with Hashimoto thyroiditis and a 1.2-cm, hypoechoic oval nodule in the left upper lateral portion of the thyroid. She returned a decade later with a 2.2-cm, hypervascular mass on ultrasound. Parathyroid hormone was mildly elevated at 90 pg/mL (reference range is 15 to 65 pg/mL), but she had persistently normal levels of total serum calcium at 9.9 mg/dL (reference range is 8.7 to 10.3 mg/dL), phosphorus at 3.5 mg/dL (reference range is 2.1 to 4.5 mg/dL), and albumin at 4.4 g/dL (reference range is 3.6 to 4.8 g/dL). She had elevated ionized calcium of 5.9 mg/dL (reference range is 4.5 to 5.6 mg/dL). Computed tomography with contrast of the neck revealed an enhancing oval lesion abutting the superior pole of the left thyroid with attenuation characteristics similar though slightly different from the thyroid. 99mTc-Sestamibi scan showed increased uptake posterior to the superior aspect of the left thyroid. Bone densitometry showed osteoporosis of the left distal radius and osteopenia of the left femoral neck. Minimally invasive radio-guided parathyroidectomy was performed with normalization of parathyroid hormone. Pathology confirmed a 1.715-g parathyroid adenoma. Conclusion Despite normal total calcium levels, clinically significant primary hyperparathyroidism may present as a large adenoma which could appear as a hypervascular neck mass on ultrasound. A high index of suspicion based on ultrasound features and measurement of ionized calcium may be helpful in diagnosing occult, but clinically relevant primary hyperparathyroidism.