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Secondary Hyperparathyroidism
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Melissa Newman, Student NMT,
Medical College of Georgia,
Radiologic Sciences


Rocco Cuteri,
Radiology Supervisor


Cherry Lim, CNMT, Aiken Regional Medical Center, Aiken, S.C.


Mary Anne Owen, M.H.E., RT(N) Program Director,
Nuclear Medicine Technology,
Medical College of Georgia


 

Detailed Discussion (click to view)

The patient was referred to Nuclear Medicine due to hyperparathyroidism. The goal of the nuclear medicine technologist was to locate the overactive parathyroid gland(s) prior to surgery. Therefore, preoperative 99mTc-sestamibi scintigraphy with dual-phase technique was used rather than dual-isotope imaging with thallium201/pertechnetate since 99mTc-sestamibi is more sensitive (over 90%) and specific (98-100%) for localizing overactive parathyroid glands. (It is important to emphasize that parathyroid imaging with 99mTc-sestamibi is a localizing study, not a diagnostic study. Many surgeons prefer to locate the gland(s) before surgery because it allows for a shorter operation, and therefore, less strain on both the surgeon and patient).


The mechanism for 99mTc-sestamibi imaging involves uptake by both the thyroid and parathyroid glands, with rapid washout of the radiotracer by the thyroid and normal parathyroid glands. If there are any overactive parathyroid glands, then radiotracer will not washout as quickly and will be visible on the 2-hour delay image. For the current patient, the delay image reveals washout of tracer from the thyroid with two areas of radiotracer accumulation, one on each of the lower right and left thyroid lobes.


According to The Journal of the American College of Surgeons, 87% of all patients with hyperparathyroidism have one hyper-functioning gland and three normal glands, which is consistent with a parathyroid adenoma (benign tumor). When two hyper-functioning glands on opposite lobes are identified, then hyperparathyroidism is usually due to hyperplasia, or enlargement of the parathyroid glands. Since the current patient has an area of increased tracer uptake on each of the thyroid lobes, the radiologist [attributed] the hyperparathyroidism to hyperplasia rather than to adenoma.


The [primary] purpose of the parathyroid glands is to control calcium levels in the blood (tight range between 8.5-10.5). Blood calcium levels are important because calcium plays an important role in many bodily functions, such as nerve impulse, muscle contraction, and blood clotting. Therefore, normal parathyroid functioning is vital to maintain homeostasis within the body.


Although the parathyroid glands are small, they are very vascular. As the blood flows through the glands, the glands detect the amount of calcium present in the blood and react by making more or less parathyroid hormone (PTH). If more calcium is needed in the blood, then more PTH is released. PTH promotes the release of calcium ions from bone, activates vitamin D and increases calcium absorption from the kidneys, and increases calcium absorption from food. A higher than normal level of calcium ions in the blood stimulates the thyroid gland to release calcitonin, an antagonist to PTH. When this negative feedback mechanism [compromised], then parathyroid diseases result such as hyperparathyroidism (too much PTH, therefore too much blood calcium) or hypoparathyroidism (too little PTH).


Since the kidneys play an important part in the feedback mechanism for maintaining adequate blood calcium levels, proper renal function is vital for homeostasis. Because the current patient has end-stage renal disease, his body is out of homeostasis, and therefore, he is undergoing the effects of hyperparathyroidism in addition to renal disease. Because his kidneys do not function properly, calcium absorption from the kidneys that is required to maintain blood calcium levels is not taking place. In addition, the patient is on dialysis, which also withdraws calcium out of the blood. Therefore, the parathyroid has to work extra hard to try to maintain proper blood calcium levels. As a result, two of the patient's parathyroid glands have hypertrophied in response to the chronic low serum calcium and are now releasing too much PTH, which causes secondary hyperpoarathyroidism.


There are several potential dangers of hyperparathyroidsm. These dangers include severe osteoporosis and/osteopenia, bone fractures, and kidney stones. If hyperparathyroidsm persists, peptic ulcers, pancreatitis, and nervous system disorders may also result. Therefore, in order to reduce the patient's rist of developing any of these disorders, the patient underwent parathyroidectomy after the overactive glands were localized via 99mTc-sestamibi scintigraphy.

 


Findings

Anterior head, neck and upper chest (excluding the heart) images were obtained approximately 15 minutes after administration of [25 mCi of 99mTc-Sestamibi] via intravenous injection, for immediate static views of the parathyroid glands, and then 2-hour delay images were obtained of the same anatomic regions. In the immediate view, there is normal uptake in the thyroid, parathyroid, and salivary glands. In the delay view, there is incomplete clearance and abnormal tracer uptake in the lower right and left parathyroid glands, with the right lower gland having the heaviest tracer accumulation. Since two parathyroid glands on opposite thyroid lobes failed to clear, the hyperparathyroidsm was confirmed and is indicative of parathyroid hyperplasia rather than adenoma [which is indicated by unilateral residual focal activity].



Clinical History

The patient is a 56-year-old black male who was admitted into the hospital for pulmonary edema. He has end-stage renal disease secondary to hypertension. He underwent chronic dialysis in 1987 and than had a cadaveric kidney transplant in 1993, which was slowly rejected. In 1994, the patient had the transplanted kidney removed, and he was then placed on hemodialysis. Upon arrival to the emergency room, it was discovered that the patient missed his dialysis. Therefore, his main complaints consisted of shortness of breath and severe cramping due to central fluid overload (radiography concluded pulmonary edema). He also complained of abdominal pain, nausea, and muscle weakness. In addition, the patient had excessively elevated PTH levels (over 200 pg/ml; normal levels: 12-72 pg/ml), and the administration of vitamin D3 failed to lower the PTH level. Therefore, the patient was referred to the Nuclear Medicine Department in order to evaluate for hyperparathyroidism and localize the overactive parathyroid gland(s).



Procedure


Radiopharmaceutical: 25 mCi 99mTc-Sestamibi



Pt. Prep

(1) Verify correct patient (2) Take patient history (3) Explain Procedure with emphasis on importance of staying immobile during imaging.



Imaging

For Dual-phase imaging (immediate and delay images), patient supine with head tilted upward with [neck] hyper extended. May tape head to table to minimize movement.


Instrumentation and Views: LEAP Collimator, 256X256 matrix (magnification 2, 1 frame at 600 sec/frame) Delay imaging at 2 hours with same parameters as the immediate image.



References (click to view)

Cuteri, Rocco, CNMT, Radiology Supervisor, Aiken Regional Medical Center, Aiken, S.C. Interview, November 15, 2000


Early, Paul J., DABSNM, ABMP and Sodee, D. Bruce, M.D., F.A.C.P. (1995) Principles and Practice of Nuclear Medicine. St. Louis: Mosby.


Grabowski, Sandra, and Tortora, Gerard. (1996). Principles of Anatomy and Physiology. New York: Harper Collins Publishers, Inc.

 

Shackett, Pete, (2000). Nuclear Medicine Technology: Procedures and Quick Reference. Philadelphia: Lippincott Williams & Wilkens.