Case Report: Familial Hypocalciuric Hypercalcaemia and Hashimoto's Thyroiditis

Area of Science:

• Endocrinology
• Surgical Pathology
• Genetics

Background:

• Hypercalcaemia is commonly caused by primary hyperparathyroidism, managed by parathyroidectomy.
• Familial hypocalciuric hypercalcaemia (FHH) is a rare differential diagnosis where parathyroidectomy is ineffective.

Observation:

• A 53-year-old female presented with hypercalcaemia and elevated parathyroid hormone, initially diagnosed with primary hyperparathyroidism.
• Post-parathyroidectomy, hypercalcaemia persisted, leading to a diagnosis of FHH.
• An incidental finding of a lymph node metastasis (suspected follicular variant papillary thyroid carcinoma) during surgery led to a second extensive surgery.

Findings:

• Histopathology of the second surgery revealed normal parathyroid glands and Hashimoto's thyroiditis, not thyroid cancer.
• The initial lymph node finding was revised to an accessory thyroid nodule with Hashimoto's thyroiditis.
• Hypercalcaemia resolved after thyroid and parathyroid tissue resection.

Implications:

• This case highlights diagnostic challenges in hypercalcaemia, potentially leading to invasive procedures.
• Misdiagnosis of follicular variant papillary thyroid carcinoma resulted in a second, more extensive surgery.
• Genetic testing for FHH should be considered in ambiguous hypercalcaemia cases, irrespective of family history.