Korean J Radiol.  2013 Jun;14(3):501-509. 10.3348/kjr.2013.14.3.501.

Diffuse Thyroid Uptake Incidentally Found on 18F-Fluorodeoxyglucose Positron Emission Tomography in Subjects without Cancer History

• Lee JY
• Choi JY
• Choi YH
• Hyun SH
• Moon SH
• Jang SJ
• Choe YS
• Lee KH
• Kim BT

• KMID: 1705467
• DOI: http://doi.org/10.3348/kjr.2013.14.3.501

Abstract

OBJECTIVE
We investigated the clinical significance of incidental diffuse thyroid uptake (DTU) on 18F-FDG PET in subjects without a history of cancer.
MATERIALS AND METHODS
This study included 2062 studies from adults who underwent 18F-FDG PET as a cancer screening program. Subjects were divided into the following two groups: with (group I) or without (group II) DTU. The presence of DTU and the thyroid visual grading score were compared with thyroid function tests, serum anti-microsomal antibody (AMA) levels, and the presence of diffuse parenchymal change (DPC) on ultrasonography (USG).
RESULTS
DTU was found in 6.6% of the scans (137/2062). Serum thyroid stimulating hormone (TSH) and AMA levels were significantly higher in group I than in group II. Increased AMA level (55.1%) and DPC (48.7%) were more frequently found in group I (p < 0.001). The proportion of subjects with any abnormal results in serum free thyroxine, triiodothyronine, TSH, or AMA levels or DPC on USG was significantly higher in group I than in group II (71.5% vs. 10.6%, p < 0.001), and was significantly and gradually increased according to the visual grading score group (0 vs. 1-2 vs. 3-4 = 10.6% vs. 58.5% vs. 90.9%, p < 0.001). TSH and is AMA levels were significantly increased according to the visual grading score.
CONCLUSION
The presence or degree of incidental DTU on 18F-FDG PET is closely correlated with increased serum AMA and TSH levels, and the presence of DPC on USG. Therefore, the most plausible pathological cause of DTU may be cell damage by an autoimmune mechanism.

Keyword

Positron emission tomography; 18F-Fluorodeoxyglucose; Diffuse thyroid uptake; Autoimmune thyroid disease

MeSH Terms

Adult
Aged
Aged, 80 and over
Antibodies/blood
Female
Fluorodeoxyglucose F18/*diagnostic use/pharmacokinetics
Humans
*Incidental Findings
Male
Microsomes/immunology
Middle Aged
Neoplasms
Positron-Emission Tomography/methods
Radiopharmaceuticals/*diagnostic use/pharmacokinetics
Retrospective Studies
Thyroid Gland/metabolism/*radionuclide imaging/ultrasonography
Thyrotropin/blood
Young Adult
Antibodies
Fluorodeoxyglucose F18
Radiopharmaceuticals
Thyrotropin

Figure

• 

  Fig. 1 Representative cases of visual grading score. A. Grade 0 with euthyroid and normal serum anti-microsomal antibody (AMA) level. B. Grade 2 with euthyroid and increased serum AMA level. C. Grade 4 with subclinical hypothyroidism and elevated serum AMA level.

• 

  Fig. 2 Visual thyroid uptake score according to thyroid functional status (error bars; 95% CI for mean). CI = confidence interval

• 

  Fig. 3 Differences in T3, FT4, TSH, and AMA levels according to visual grading score group. T3 (A), FT4 (B), TSH (C), and AMA (D) levels (error bars; 95% CI for mean). T3 = triiodothyronine, FT4 = free thyroxine, TSH = thyroid stimulating hormone, AMA = anti-microsomal antibody

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