Question

A 21-year-old male visits with his family doctor at the urging of his parents when home for Spring Break. The parents are concerned because their son has lost a significant amount of weight. The young man is concerned because he is experiencing a heart rate of 120bpm while at rest and much higher when exercising. Additionally, his blood pressure averages 137/82 based upon four recordings. He has a recurring headache, tremors in his hands and suffers dyspnea.

This individual has been generally health for his entire life, eats a reasonably good diet and is very active, thus the above symptoms are concerning. Standard blood tests show normal levels of blood cells, however there is an elevated amount of metadrenalines (metabolite by-product of adrenaline) and the urinalysis also shows an elevated amount of metabolites of catecholamines. The physician then orders a 24-hour urine test where the patient collects urine at regular intervals for a 24-hour period. The patient is warned to avoid stimulants such as cocoa and caffeine during this time period. The results of this test confirm elevated metabolites of catecholamines. The physician suspects a condition called pheochromocytoma, which is a (usually) non-cancerous tumor of the adrenal gland. This tumor causes the excess secretion of catecholamines. To confirm this suspicion, the physician orders a specialized type of CT scan, called MBIG. This type of scan utilizes radioactive iodine as a contrast agent for visualization of masses as described above. A sample of MIBG results is shown below:

The MIBG confirms the presence of a tumor on the adrenal gland and the young man is scheduled for surgery to remove the mass. It is non-cancerous and he resumes his life. As a side note, current estimates are that only about 10% of adrenal tumors are cancerous.

6. The MIBG is an FDA approved test, however there are severe warnings of thyroid damage as a result of this test. What is iodine normally used for in the thyroid? Based on the normal use of iodine by the thyroid, which type of cells in the thyroid might be damaged by radioactive iodine? (2 pts)

Answer 1

6. Thyroid gland is endocrine organ that produces thyroid hormone (T3 and T4). For this process iodine is essential. Thyrocyte (or Follicular cells of thyroid) pumps iodine from blood into thyroid follicle. Iodine then combines with tyrosine residue of thyroglobulin to form thyroid hormone. In MIBG scan radioactive iodine is used. If this radioactive iodine is taken up by thyrocytes then it may cause damage to these cells and will lead to impairment of thyroid gland function. (Radioactive iodine is also used for hyperthyroidism)