Clinical practice. Primary hyperparathyroidism

Bone disease in primary hyperparathyrodism

Nowadays, primary hyperparathyroidism (PHPT) is mostly a mild disease. Overt skeletal manifestations are rare but decreased bone mineral density (BMD) can still be demonstrated. Even in mild cases, excess parathyroid hormone (PTH) increases bone turnover leading to bone loss particularly at cortical sites. Conversely, a relative preservation of cancellous bone has been shown by histomorphometric analyses and advanced imaging techniques. An increased fracture rate has been demonstrated in untreated patients with PHPT at peripheral sites and in the spine. Parathyroidectomy (PTx) is the definitive cure for PHPT. With the restoration of normal PTH, bone resorption is quickly tapered down, while bone formation proceeds at the level of bone multicellular units, which were activated prior to PTx. The rapid refilling of the enlarged remodeling space and the subsequent matrix mineralization will result in an increase in BMD at sites rich in trabecular bone, such as lumbar spine and hip, which mainly occurs during the first 6-12 months after PTx. Cortical bone is less responsive to PTX because of the low rate of bone turnover, but sensible increases in BMD at the distal third of the radius can be observed in the long term. PTx seems to decrease the risk of fractures but more data are needed before a definitive conclusion on this important matter can be reached. Treatment with bisphosphonates can be considered for patients with low BMD who do not undergo PTx. Two-year treatment with alendronate has been shown to decrease bone turnover markers and increase BMD at the lumbar spine and hip, but not at the distal radius. Cinacalcet stably decreased serum calcium levels across a broad range of PHPT severity, but no change in BMD occurred in patients treated for up to 5.5 years.

Primary hyperparathyroidism in children and adolescents

Primary hyperparathyroidism (PHPT) is a common endocrine disorder in adults in whom the typical presentation is incidentally discovered as asymptomatic hypercalcemia. PHPT is much less common in children and adolescents, but has greater morbidity in this age group, as most young patients with PHPT will have symptomatic hypercalcemia or complications such as kidney stones, abdominal pain, and skeletal fragility. An important feature of PHPT in younger patients is the relatively high prevalence of germline inactivating mutations of the CASR gene, which encodes the calcium-sensing receptor. Biallelic CASR mutations cause neonatal severe hyperparathyroidism, a life-threatening condition that presents within days of life with marked hypercalcemia, respiratory distress, failure to thrive, and skeletal demineralization. By contrast, more common heterozygous CASR mutations are generally associated with a benign variant of PHPT termed familial hypocalciuric hypercalcemia. Appropriate management of PHPT in children and adolescents requires distinction between familial hypocalciuric hypercalcemia, which generally requires no specific treatment, and other forms of PHPT that are best treated by parathyroidectomy.

Primary hyperparathyroidism due to an intrathyroidal parathyroid adenoma associated with chronic lymphocytic thyroiditis

This is a case of a 44-year-old woman with an anterior neck mass and hypothyroidism who presented with an incidental finding of an elevated serum calcium level and was found to have primary hyperparathyroidism and osteoporosis. During surgical exploration no parathyroid adenoma was found, although a nodule was palpated within the right thyroid lobe. Examination of the excised right thyroid lobe revealed an intrathyroidal parathyroid adenoma and chronic lymphocytic thyroiditis. After surgery, she did not develop severe hypocalcaemia and this was attributed to preoperative treatment with pamidronate. In the months following surgery, parathyroid hormone remained undetectable.