Keywords
Autonomous thyroid adenoma - esophageal 99 mTc uptake - hyperthyroidism - subacute
thyroiditis - technetium-99m pertechnetate thyroid scan - thyrotoxicosis
INTRODUCTION
Radioiodine or technetium-99m-pertechnetate (99mTc) thyroid scans are frequently used
in the evaluation of thyrotoxicosis. Uptake of radioiodine or 99mTc by thyrocytes
is attributed to the sodium-iodide symporter (NIS).[1] Expression of NIS in several non-thyroidal tissues causes physiological uptake of
iodine and 99mTc in those tissues.[2],[3],[4]
Painful subacute thyroiditis (SAT) is characterized by thyroid gland inflammation,
typically presenting with neck pain, thyroid tenderness, and dysfunction. Radioiodine
or 99mTc scan typically shows markedly decreased tracer uptake.
We present herein a very rare case of SAT misdiagnosed as an autonomous thyroid adenoma
most likely due to 99mTc uptake in the esophagus.
CASE PRESENTATION
A medically free 60-year-old male patient presented to our endocrinology clinic with
pain and swelling in the anterior aspect of his neck of 1-week duration. Three weeks
prior to his presentation, he had an upper respiratory tract infection. Clinically
the patient was euthyroid.
On examination, his pulse rate was 105 beats per minute and regular and his blood
pressure was 145/85mm Hg. Thyroid examination showed a tender small goiter. He had
no retrosternal goiter, bruits, or cervical lymphadenopathy. The rest of the examination
was unremarkable. Laboratory values showed an elevated serum free T4 and free T3 and
a suppressed thyroid-stimulating hormone (TSH) [Table 1]. Erythrocyte sedimentation rate (ESR) was 80mm in the first hour. His white cell
count was 8.54 × 109/L with a normal differential. The blood film showed occasional
hypersegmented neutrophils.
Table 1
Laboratory values of the patient
|
Date
|
Free T4
|
Free T3
|
TSH
|
ESR
|
Comment
|
|
9.01-19.05 (pmol/L)
|
1.71-3.71 (pmol/L)
|
0.35-4.94 (mU/L)
|
0-25 (mm/1st h)
|
|
TSH = thyroid-stimulating hormone, ESR = erythrocyte sedimentation rate
|
|
March 3
|
44.08
|
11.14
|
0.009
|
80
|
Propranolol was started.
|
|
March 8
|
|
|
|
|
Technetium-99m-pertechnetate thyroid scan was performed. The patient was diagnosed
with toxic thyroid adenoma. Carbimazole was started.
|
|
March 16
|
22.16
|
7.21
|
0.01
|
29
|
Thyroid ultrasound was performed. Carbimazole was discontinued and propranolol was
tapered.
|
|
April 1
|
8.78
|
3.23
|
5.28
|
10
|
|
|
April 29
|
5.86
|
3.19
|
64.34
|
7
|
The patient required a short course of thyroxine therapy
|
|
May 28
|
12.01
|
|
4.03
|
|
Thyroid ultrasound, scan, and uptake were repeated.
|
|
|
|
|
|
Antithyroglobulin antibodies were tested and came positive.
|
|
August 1
|
15.20
|
|
1.50
|
|
|
Initial clinical diagnosis was SAT. To confirm the diagnosis, a 99mTc scan was completed,
which showed a focus of intense uptake in the region of the inferior pole of the right
thyroid lobe with markedly suppressed uptake of the remainder of the thyroid [Figure 1]. The imaging finding was consistent with a toxic adenoma. Accordingly, the patient
was started on carbimazole and propranolol.
Figure 1: Initial thyroid scan obtained 20 min after 5 mCi (185 MBq) intravenous injection
of 99mTc-pertechnetate showing a hot focus (arrow) in the inferior pole region of
the right thyroid lobe with markedly decreased uptake of the remainder of the thyroid
Although thyroid ultrasound was ordered on presentation, it was not completed until
8 days later because the patient missed his ultrasound appointment. It revealed multiple
small hypoechoic nodules; the largest one in the superior pole of the left lobe measured
5mm × 10mm. More importantly, there was no nodule in the inferior pole of the right
lobe corresponding to the hot focus seen on his initial thyroid scan. As a result,
the diagnosis of toxic thyroid adenoma was questioned. Therefore, carbimazole was
discontinued and propranolol was tapered and discontinued.
Repeat Tc scan was performed when the patient’s serum TSH normalized [Table 1]. It showed heterogeneous tracer uptake with a warm nodule in the inferior pole of
the left thyroid lobe [Figure 2]. The hot focus in the inferior right lobe (which was presumed to be an autonomous
adenoma) was no longer seen. A repeat thyroid ultrasound did not reveal significant
changes. The final diagnosis was SAT in a patient with multinodular goiter with no
scintigraphic evidence of autonomous adenoma.
Figure 2: The follow-up 99mTc-pertechnetate scan showing heterogeneous tracer uptake with a
warm nodule in the left inferior pole and a cold nodule laterally in the mid left
lobe (arrows). There was no evidence of the right inferior pole hot nodule
DISCUSSION
This case highlights the potential pitfalls associated with interpretation of thyroid
Tc scan in patients with thyrotoxicosis.
Our patient presented with thyrotoxicosis and clinical manifestations suggestive of
SAT. Typically the thyroid Tc scan during the thyrotoxic phase of SAT is characterized
by diffusely decreased uptake, although slightly inhomogeneous tracer distribution
is sometimes observed. A focus of increased uptake is unusual and warrants further
investigation.[5] The initial thyroid Tc scan of our patient showed a single focus of increased uptake
in the region of the inferior pole of the right lobe of the thyroid [Figure 1]. The absence of an ultrasound nodule corresponding to the site of the hot focus
indicates that the radioactive focus was extrathyroidal. Potential extrathyroidal
sites include the trachea, esophagus, and bone marrow of the vertebrae corresponding
to the level of the thyroid gland.
Radiotracer uptake in the bone marrow of the femora and tibiae bones has only been
reported in an athletic runner.[6] Radiotracer uptake in the vertebral bone marrow has not been reported. Our patient
was not involved in heavy running activities and was not known to have a bone marrow
disorder. Esophageal uptake has been reported in Zinker’s diverticulum, epinephric
diverticulum, achalasia, and scarring of the esophagus.[7] However, because the hot focus in our patient’s thyroid scan was not seen on the
repeat scan it is most likely that the hot focus was due to a temporary cause rather
than a fixed one. This makes the aforementioned esophageal and bone marrow disorders
unlikely to be the cause of the thyroid activity observed. Tracheal uptake was reported
with the use of aerosol drugs.[8] Our patient was not using any local aerosol, making it unlikely that the observed
hot focus was located in the trachea.
Based on the above, transient Tc activity in the esophagus was the most likely explanation
for our patient’s thyroid scan finding. It is widely known that retention of saliva
and/or refluxed gastric secretions in the esophagus can explain radiotracer uptake
in the esophagus.[9] Asking the patient to drink water just prior to the scan can minimize this problem
by washing tracer activity in the esophagus.[10] Our conclusion is limited by the fact that thyroid ultrasound was performed 8 days
after the thyroid Tc scan. However, we think that this difference in time between
the two imaging studies is of no significance. In conclusion, the uniqueness of our
case is that it represents an esophageal Tc uptake mimicking an autonomous thyroid
adenoma in a patient with SAT. The esophageal uptake was most likely due to retention
of saliva and/or refluxed gastric secretions. This highlights the importance of correlating
thyroid nuclear scan with ultrasonographic findings and clinical presentation.
