Naifa L. Busaidy, MD, Kamal F. Busaidy, BDS, FDSRCS, Sai-Ching Jim Yeung, MD, PhD

Disclosures

February 28, 2005

Discussion

The case of this unfortunate patient presents several points of interest. Brown tumors are rare, seen in fewer than 5% of patients with primary hyperparathyroidism today. Early detection of hypercalcemia due to rapid multichannel biochemical measurements helps to limit the ravages of advanced hyperparathyroidism. This patient is very unusual in that he came to medical attention because of the maxillary tumor.

Another interesting feature is that this patient developed pulmonary embolism with no symptoms at all. There are only a few cases of patients with parathyroid carcinoma and embolic phenomena in published series.

Parathyroid carcinoma is a rare disease comprising between 0.5% and 4% of all cases of primary hyperparathyroidism. It affects both genders equally and occurs predominantly during the 4th to 6th decades of life, although a wide age range is seen. The etiology of the disease is unknown. In patients with a history of radiation exposure, there is an increased incidence of parathyroid adenomas, but there is no specific increased incidence of parathyroid carcinoma.

The diagnosis of parathyroid carcinoma in the absence of regional or distant metastases is challenging. Markedly elevated serum calcium levels (> 14 mg/dL), very high serum iPTH levels (5 times the upper limit of normal), a palpable neck mass, and laryngeal nerve palsy are clinical hints to the diagnosis. During surgical resection, the diagnosis may be suspected by the presence of a gray, firm, adherent parathyroid gland with evidence of local invasion. Fine needle aspiration should not be performed before surgery, because this may cause seeding of tumor cells along the needle track and increase the risk of recurrent disease.

Pathologic criteria may not differentiate parathyroid carcinoma definitively from the more common adenoma. Though there are established histopathologic criteria for the diagnosis of parathyroid carcinoma, the histologic diagnosis remains a challenge. Many of the classic features are not present in carcinomatous glands, and, not infrequently, some of these features may be present in a benign adenoma. Immunohistochemistry and molecular histopathology may in the future assist in the differentiation of parathyroid carcinoma from the more common adenoma.

Unfortunately, the diagnosis of parathyroid carcinoma is often made only when the patient returns with recurrent or metastatic disease, sometimes many years after the initial diagnosis. This emphasizes the need for lifetime monitoring of serum calcium levels in the patient who has undergone resection of a parathyroid "adenoma."

Preoperative diagnosis is ideal, as adequate treatment of the primary lesion should include en bloc resection of the tumor with areas of potential invasion. The area resected should include the tumor, the adjacent thyroid lobe, ipsilateral central neck contents including tracheo-esophageal soft tissues and lymphatics, and any adherent structures. This is obviously too radical a procedure for the vast majority of benign adenomas.

Patients with parathyroid carcinoma experience recurrences between 35% and 80% of the time. Cure after recurrence is rare, although aggressive resection of recurrent disease has been shown to prolong disease-free intervals and control hypercalcemia.

Radiation therapy may play a role as adjuvant treatment after surgery for patients thought to be at high risk of recurrence. Chemotherapy has not been shown to be effective.

Parathyroid carcinoma is a disease with an often indolent but progressive course.

The morbidity and mortality are generally due to excessive PTH secretion and hypercalcemia, rather than to the tumor burden itself. Treatment modalities for hypercalcemia, especially in patients with unresectable disease or without measurable disease, are of utmost importance. Conventional treatment with intravenous fluids, diuretics, and antiresorptive agents such as bisphosphonates, gallium, or mithramycin helps to control or ameliorate hypercalcemia. However, therapies such as calcimimetic agents that focus on decreasing PTH secretion may be better to prevent complications and improve survival in patients with no curable disease. An interdisciplinary team approach involving endocrinologists, surgeons, radiation therapists, and pathologists offers patients the best option for cure of this rare disease.

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