Rationale and Objectives
Thymic hyperplasia is associated with hyperthyroidism. Increased thymus 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) uptake in hyperthyroidism patients has been reported. The aim of this study was to analyze the FDG positron emission tomography (PET) thymus uptake spectrum in patients with active hyperthyroidism with correlation with serum hormones.
Materials and Methods
The prospective study included FDG PET scans from 65 hyperthyroidism patients and 30 subjects with euthyroid status as control group. The intensity of FDG uptake in thyroid and thymus regions was graded subjectively on a five-point scale and semi-quantitatively by measuring standard uptake value (SUV). Correlation coefficient between thymus SUV and serum thyroxine, triiodothyronine, thyrotropin, thyroid peroxidase antibodies (TPO Ab), thyrotropin receptor autoantibody (TR Ab), and thymulin were analyzed.
Results
Among 65 hyperthyroidism patients, 30 (46.2%) and 39 (60%) patients showed thyroid and thymus FDG uptake, respectively. The frequency of thymus uptake FDG was high in patients younger than age 40 (28/31, 90.3%). The patterns of the thymic FDG uptake include inverted V or triangular, separated triangular, united nontriangular, unilateral right or left extension, and focal midline. Focal midline FDG uptake was the most common pattern (15/39, 38.5%). None of the control group showed thymus FDG uptake. The correlation coefficient between the FDG uptake SUV levels in thymus and serum hormones, thyrotropin, TPO Ab, TR Ab, and thymulin levels were all low ( P > .05).
Conclusions
In FDG PET scan, thymus activity was common in hyperthyroidism patients; this should not be misdiagnosed as a malignancy in patients exhibiting weight loss.
It has been reported that thymic hyperplasia is associated with Graves’ disease . In most cases, thymic hypertrophy is minimal and unapparent. Therefore, radiologically detectable thymic enlargement as an anterior mediastinal mass with thyrotoxicosis has not been frequently reported . The thymic hyperplasia resolution with the reversibility of the hyperthyroid state has been reported by measuring the size of thymus on x-ray computed tomography (CT) .
It has been reported that classic symptoms and signs of hyperthyroidism are significantly less prevalent in older patients . The only three signs found in more than 50% of older patients with hyperthyroidism were tachycardia, weight loss, and fatigue . The latter two signs may raise the suspicious of undiagnosed malignancy in elderly patients. If hyperthyroidism is highly suspected, thyroid function test should be performed first to search the underlying disease.
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Materials and methods
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SUV=(activityintheROI[MBq/mL])/(injecteddose[MBq]/patient’sweight[kg]). SUV
=
(
activity
in
the
ROI
[
MBq
/
mL
]
)
/
(
injected
dose
[
MBq
]
/
patient
’
s
weight
[
kg
]
)
.
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Results
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Table 1
Age-related Distribution of FDG Uptake in Thyroid and Thymus Regions of Hyperthyroidism Patients
Age (y) Patients ( n = 65) Thyroid Thymus SUV (mean ± SD) + ( n = 30) – ( n = 35) SUV (mean ± SD) + (n = 39) – ( n = 26) ≤20 2 1.33 ± 0.33 0 2 2.58 ± 0.76 2 0 21–30 17 1.35 ± 0.64 3 14 1.71 ± 0.54 16 1 31–40 12 1.43 ± 0.34 9 3 1.66 ± 0.35 ∗ 10 2 41–50 20 1.73 ± 1.00 13 7 1.26 ± 0.37 ∗ 9 11 >50 14 1.55 ± 0.74 5 9 1.34 ± 0.54 ∗ 2 12
+, 18 F-FDG uptake; –, no 18 F-FDG uptake; 18 F-FDG, 2-[fluorine-18]fluoro-2-deoxy-D-glucose; SD, standard deviation; SUV, standard uptake value.
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![Figure 1, The age-related distribution of 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) uptake in thyroid and thymus regions of hyperthyroidism patients.](https://storage.googleapis.com/dl.dentistrykey.com/clinical/TheFrequencyandSpectrumofThymus2Fluorine18Fluoro2deoxyDglucoseUptakePatternsinHyperthyroidismPatients/0_1s20S1076633211002601.jpg)
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![Figure 2, Patterns of the thymic 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) uptake in Graves’ disease patients. (a) Inverted V or triangular pattern with grade +3 uptake thymus in a 25-year-old female, (b) separated triangular pattern with grade +3 uptake thymus in a 48-year-old female, (c) separated nontriangular pattern with grade +3 uptake thymus in a 30-year-old female, (d) unilateral right extension pattern with grade +2 uptake in a 22-year-old female, (e) focal midline pattern with grade +2 uptake in a 32-year-old female, and (f) unilateral left extension pattern with grade +2 uptake in a 41-year-old female.](https://storage.googleapis.com/dl.dentistrykey.com/clinical/TheFrequencyandSpectrumofThymus2Fluorine18Fluoro2deoxyDglucoseUptakePatternsinHyperthyroidismPatients/1_1s20S1076633211002601.jpg)
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![Figure 3, (a) The 2-[fluorine-18]fluoro-2-deoxy-D-glucose positron emission tomography (FDG PET) maximum intensity projection (MIP) image of a 41-year-old female for cancer screening showed mild FDG uptake in bilateral thyroid gland with normal thyroid function. (b) The subject had another FDG PET/CT scan 2.5 years later with symptom of hand tremor. The MIP image revealed moderately increased FDG uptake (grade 3+) in thyroid gland and in the thymus ( arrow ). Thyroid function tests showed decreased serum thyrotropin level (0.06 μU/mL, normal 0.4–5.0 μU/mL) accompany with increased serum T4 (17 μg/dL, normal 4.5–12 μg/dL), and free T4 (1.88 ng/dL, normal 0.93–1.7 ng/dL) levels.](https://storage.googleapis.com/dl.dentistrykey.com/clinical/TheFrequencyandSpectrumofThymus2Fluorine18Fluoro2deoxyDglucoseUptakePatternsinHyperthyroidismPatients/2_1s20S1076633211002601.jpg)
![Figure 4, Change of thymus 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) uptake in eight subjects from active Graves’ disease state (standard uptake value [SUV] 1.33 ± 0.6) to posttreatment normal thyroid state (SUV 0.99 ± 0.15) ( P < .01). Closed circles represent individual cases, open circles represent mean values, and error bars indicate standard deviation (SD).](https://storage.googleapis.com/dl.dentistrykey.com/clinical/TheFrequencyandSpectrumofThymus2Fluorine18Fluoro2deoxyDglucoseUptakePatternsinHyperthyroidismPatients/3_1s20S1076633211002601.jpg)
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Discussion
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![Figure 5, The coronal (a) computed tomography (CT), (b) positron emission tomography (PET), and (c) PET/CT fusion images of the 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) PET/CT study of a 25-year-old female Graves’ disease patient showed faintly (grade 1+) increased metabolic activity of FDG in the thyroid ( arrow ). Intensely increased (grade 4+) FDG uptake in the thymus ( arrowheads ) extends from left neck to the right anterior upper mediastinum. The serum thyrotropin level was not measurable (<0.1 μU/mL), both T4 (24 μg/dL, normal 4.5–12 μg/dL) and T3 (318 ng/dL, normal 80–180 ng/dL) serum levels increased.](https://storage.googleapis.com/dl.dentistrykey.com/clinical/TheFrequencyandSpectrumofThymus2Fluorine18Fluoro2deoxyDglucoseUptakePatternsinHyperthyroidismPatients/4_1s20S1076633211002601.jpg)
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Conclusion
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References
1. Murakami M., Hosoi Y., Negishi T., et. al.: Thymic hyperplasia in patients with Graves’ disease. Identification of thyrotropin receptors in human thymus. J Clin Invest 1996; 98: pp. 2228-2234.
2. Carvalho M.R., Dias T., Baptista F., et. al.: Graves’ disease and massive thymic hyperplasia. Thyroid 2010; 20: pp. 227-229.
3. Rice R.D., Parker D.M., Gallo D.M., et. al.: Persistent anterior mediastinal mass in a patient with Graves’ disease. Am Surg 2010; 76: pp. 113-115.
4. Takami K., Omiya H., Higashiyama M., et. al.: A case report of large thymic hyperplasia associated with hyperthyroidism. Ann Thorac Cardiovasc Surg 2009; 15: pp. 404-407.
5. Popoveniuc G., Sharma M., Devdhar M., et. al.: Graves’ disease and thymic hyperplasia: the relationship of thymic volume to thyroid function. Thyroid 2010; 20: pp. 1015-1018.
6. Boelaert K., Torlinska B., Holder R.L., et. al.: Older subjects with hyperthyroidism present with a paucity of symptoms and signs: a large cross-sectional study. J Clin Endocrinol Metab 2010; 95: pp. 2715-2726.
7. Trivalle C., Doucet J., Chassagne P., et. al.: Differences in the signs and symptoms of hyperthyroidism in older and younger patients. J Am Geriatr Soc 1996; 44: pp. 50-53.
8. Kwee T.C., Basu S., Cheng G., et. al.: FDG PET/CT in carcinoma of unknown primary. Eur J Nucl Med Mol Imaging 2010; 37: pp. 635-644.
9. Yapar Z., Kibar M., Yapar A.F., et. al.: The value of 18F-fluorodeoxyglucose positron emission tomography/computed tomography in carcinoma of an unknown primary: diagnosis and follow-up. Nucl Med Commun 2010; 31: pp. 59-66.
10. Nishizawa S., Kojima S., Teramukai S., et. al.: Prospective evaluation of whole-body cancer screening with multiple modalities including [18F]fluorodeoxyglucose positron emission tomography in a healthy population: a preliminary report. J Clin Oncol 2009; 27: pp. 1767-1773.
11. Terauchi T., Murano T., Daisaki H., et. al.: Evaluation of whole-body cancer screening using 18F-2-deoxy-2-fluoro-D-glucose positron emission tomography: a preliminary report. Ann Nucl Med 2008; 22: pp. 379-385.
12. Chen Y.K., Chen Y.L., Liao A.C., et. al.: Elevated 18F-FDG uptake in skeletal muscles and thymus: a clue for the diagnosis of Graves’ disease. Nucl Med Commun 2004; 25: pp. 115-121.
13. Jerushalmi J., Frenkel A., Bar-Shalom R., et. al.: Physiologic thymic uptake of 18F-FDG in children and young adults: a PET/CT evaluation of incidence, patterns, and relationship to treatment. J Nucl Med 2009; 50: pp. 849-853.
14. Turkyilmaz A., Eroglu A., Aydin Y., et. al.: A new risk factor in oesophageal cancer aetiology: hyperthyroidism. Acta Chir Belg 2010; 110: pp. 533-536.
15. Shu X., Ji J., Li X., et. al.: Cancer risk in patients hospitalised for Graves’ disease: a population-based cohort study in Sweden. Br J Cancer 2010; 102: pp. 1397-1399.
16. Rini J.N., Leonidas J.C., Tomas M.B., et. al.: 18F-FDG uptake in the anterior mediastinum: physiologic thymic uptake or disease?. Clin Positron Imaging 2000; 3: pp. 115-125.
17. Nakahara T., Fujii H., Ide M., et. al.: FDG uptake in the morphologically normal thymus: comparison of FDG positron emission tomography and CT. Br J Radiol 2001; 74: pp. 821-824.
18. Francis I.R., Glazer G.M., Bookstein F.L., et. al.: The thymus: reexamination of age-related changes in size and shape. AJR Am J Roentgenol 1985; 145: pp. 249-254.
19. Shah U.K., Fuleihan N.S., Handler S.D., et. al.: Pathologic quiz case 2. Cervical thymus. Arch Otolaryngol Head Neck Surg 1999; 125: pp. 695-698.
20. Scheif J.M., Cordier A.C., Haumont S.: Epithelial cell proliferation in thymic hyperplasia induced by triiodothyronine. Clin Exp Immunol 1977; 27: pp. 516-521.
21. Boerner A.R., Voth E., Theissen P., et. al.: Glucose metabolism of the thyroid in Graves’ disease measured by F-18-fluoro-deoxyglucose positron emission tomography. Thyroid 1998; 8: pp. 765-772.
22. Chen Y.K., Chen Y.L., Cheng R.H., et. al.: The significance of FDG uptake in bilateral thyroid glands. Nucl Med Commun 2007; 28: pp. 117-122.
23. Rothman I.N., Middleton L., Stack B.C., et. al.: Incidence of diffuse FDG uptake in the thyroid of patients with hypothyroidism. Eur Arch Otorhinolaryngol 2011; Feb 16. (Epub ahead of print)
24. Nishimori H., Tabah R., Hickeson M., et. al.: Incidental thyroid “PETomas”: clinical significance and novel description of the self-resolving variant of focal FDG-PET thyroid uptake. Can J Surg 2011; 54: pp. 83-88.
25. Fabris N., Mocchegiani E., Mariotti S., et. al.: Thyroid function modulates thymic endocrine activity. J Clin Endocrinol Metab 1986; 62: pp. 474-478.
26. Fabris N., Mocchegiani E., Provinciali M.: Plasticity of neuro-endocrine-thymus interactions during aging: a minireview. Cell Mol Biol 1997; 43: pp. 529-541.