Presentation
Underyling metastatic follicular thyroid carcinoma. Done total thyroidectomy 21 years ago. Histopathology showed capsular invasions into capsular channels. Completed 3 cycles of radioiodine ablation therapies (200 mCi dosage).
Patient Data
There is a focus of moderately intense radioiodine accumulation seen in the left mid-thoracic region, corresponding to an ill-defined AP window node seen on the corresponding SPECT-CT, measuring approximately 9mm.
No significant radioiodine uptake was seen in the anterior neck. No other abnormal foci of radioiodine elsewhere in the body to indicate metastatic functioning follicular thyroid carcinoma.
Physiological radioiodine activities in the oro-nasal cavity, salivary glands, gastrointestinal tracts, liver and urinary bladder.
Case Discussion
Prior to the scan, thyroxine is withheld for at least 4 weeks in order to increase the endogenous blood thyroid stimulating hormone levels to more than 30 mU/L. However, there would be risk of hypothyroidism for witholding thyroxine.
Alternatively, intramuscular thyrogen 0.9 mg (recombinent TSH) can be given for 2 days before the oral radioiodine administration. Two days after the oral administration, scan will be done and thyroid function test and thyroglobulin levels needs to be taken.
The patient should take a low iodine diet for 14 days prior to oral administration. The patient should avoid food such as iodised salt, dairy products, eggs, seafood, canned food, soy products, vegetables, multivitamin tablets, cheese and tea. This is because normal iodine in blood can act as competitive inhibitor to radioiodine from binding to normal thyroid tissue or thyroid carcinoma cells, reducing the sensitivity of iodine-131 scan.
There should also no iodinated contrasted scan 2 to 4 weeks before the radioiodine scan.
Patient is fasted overnight and should refrain from taking plain water before the radioidine administration.
Blood investigations are taken before the administration of radioiodine.
On the day of oral administration, Iodine-131 with 5.0 mCi dosage is given orally. Patient can eat and drink 2 hours after the oral administration, Bisacodyl laxative is given for2 days for bowel evacuation after radioiodine administration.
After radioiodine administration, patient should be isolated from the children less than 12 years old, pregnant mother and public for 2 days.
The scan is done 48 hours after taking Iodine-131. Anterior and posterior whole-body scans are done together with SPECT-CT of the thorax.
Patient can resume taking thyroxine and stop the low iodine diet after the scan.
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