Primary Hyperparathyroidism

Overview

Primary Hyperparathyroidism is a disorder caused by a pathological excess of Parathyroid Hormone (PTH) secretion. Most cases of Primary Hyperparathyrodism are sporadic but they can be associated with Multiple Endocrine Neoplasia (MEN).

Etiologies

Primary Hyperparathyroidism is typically caused by solitary functional adenomas or pathological hyperplasia of the parathyroid gland's chief cells. These neoplastic or hyperplastic cells secrete PTH independent of regulatory mechanisms thus resulting in excess PTH levels.

Morphology

Solitary Adenomas typically manifest as enlargement of just one of the four parathyroid glands, are usually well-circumscribed, and composed of uniform cells. Hyperplastic disease manifests as enlargement of more than one parathyroid gland with attendant hyperplasia of parathyroid chief cells.

When PTH excess is mild, disease manifests as thinning of bone trabeculae similar to observed in osteoporosis. However, if PTH excess is severe, disease manifests as "Osteitis Fibrosa Cystica (OFC)" which involves PTH-induced proliferation of giant, multi-nucleated osteoclasts, results in intense resorption of bone. Patients with OFC may display severely thinned and scalloped cortical bone overlying bone marrow replaced with fibrous tissue that at times is hemorrhagic and cystic. When large, these masses of cystic fibrous tissue are termed "Brown Tumors" as they may be confused with neoplasms.

Clinical Consequences

In most cases Primary Hyperparathyroidism is detected as slight elevations in blood calcium prior to the development of over symptomology. When symptomology does develop, patients may present with the syndrome of hypercalcemia. Additionally, some patients display recurrent nephrolithiasis and nephrocalcinosis due to long-term excess of blood calcium concentration. Finally, pathological bone fractures due to Osteitis Fibrosa Cystica, described, above or accelerated osteoporosis is a common feature of untreated disease.

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