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When not to biopsy a hypervascular thyroid nodule
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A 66-year-old postmenopausal woman was referred for the evaluation and management of osteopenia with progressive bone loss despite adequate calcium and vitamin D supplementation. She had no family history of osteoporosis or thyroid disease and no prior history of head and neck radiation.
Stephanie L. Lee
Patient history, test results
Review of her prior laboratory testing revealed subclinical hyperthyroidism since 2010 with a suppressed thyroid-stimulating hormone of 0.01 mIU/L; normal levels of free thyroxine at 1.1 ng/dL and thyroperoxidase thyroid antibody <30 (normal, <60). On physical exam, she did not have kyphosis and a 3-cm nodule was palpated in the left thyroid lobe. The nodule was mobile and non-tender.
Repeat thyroid testing in 2013 showed similar thyroid function tests with a suppressed TSH <0.01 mIU/L with normal levels of free T4 at 1.2 ng/dL (reference range, 0.1–2.6 ng/dL) and total triiodothyronine of 153 ng/dL (reference range, 76-181 ng/dL). Thyroid-stimulating immunoglobulin was low at <89% (reference range, <140), and thyroid ultrasound showed a normal-sized thyroid gland with a solid isoechoic 3.6 cm x 1.9 cm x 2.1 cm (sagittal x anteroposterior x transverse) nodule in the left lobe (Figure 1). The nodule had a distinct margin and no calcifications. There was vigorous peripheral vascularity (blood flow around the edge of the nodule) with low-volume intranodular vascularity (inside the nodule) by Doppler analysis (grade 3 vascular flow; Table 1). A thyroid biopsy was deferred and an I-123 nuclear thyroid scan was performed. Elevated iodine uptake was seen in the large left thyroid nodule with suppressed uptake in the surrounding normal thyroid (Figure 2). The 24-hour iodine uptake was borderline elevated at 30.9% (normal, 13-31%).
Figure 1. Thyroid ultrasound. Transverse (A) and Sagittal (B) views with Doppler (C) of the heterogeneous, isoechoic nodule (red arrow) in the left lobe of the thyroid. The pattern of the vascular flow is vigorous peripheral (yellow arrow) and low flow intranodular (green arrow), consistent with grade 3 vascular flow (see table). The remainder of the thyroid ultrasound was normal.
Figure 2. I-123 thyroid scan. Four-hour scintiscan after I-123 administration showing uptake only within the hyperfunctional nodule (red arrow) in the left thyroid lobe.
‘Hot’ and ‘cold’ nodules
The initial step in the evaluation of a thyroid nodule is a TSH level. If the level is normal or elevated, the next step is a fine needle aspiration biopsy, usually with ultrasound guidance. If the TSH is suppressed, a nuclear thyroid scan, preferably with I-123, is requested. Occasionally, technetium-99m will falsely show isotope trapping, resulting in a false-negative evaluation of a thyroid nodule. I-131 is not recommended because this isotope emits beta particles that cause thyroid tissue damage. The I-123 thyroid scintiscan allows you to determine whether this is Graves’ disease or toxic multinodular goiter with a “cold” or “hot” nodule or an autonomous toxic adenoma. A cold nodule on a thyroid scintiscan will accumulate isotope less avidly than the surrounding normal thyroid tissue, whereas a hot or autonomous nodule has more uptake than the remainder of the gland (Figure 2). This is important because the risk for cancer in an autonomous nodule is extremely low. A hot autonomous nodule does not require biopsy unless there is demonstrated growth or if ipsilateral and unilateral adenopathy is detected. A cold nodule occurs in more than 80% to 85% of nuclear scans of thyroid nodules. Because almost all thyroid nodules are cold, this test most likely will not provide important information during the nodule evaluation because all of these cold nodules should be biopsied to exclude cancer.
Does this patient need treatment for her subclinical hyperthyroidism from the toxic thyroid adenoma? It is recommended that subclinical hyperthyroidism should be treated in patients aged older than 65 years because of the increased risk for bone loss and atrial fibrillation in this population at high risk for these conditions. This patient has progressive osteopenia that may have been accelerated because of the subclinical hyperthyroidism. It was recommended that she be treated either with radioactive iodine ablation or thyroid lobectomy. This patient was adamant that she did not want to take a medication after the treatment. The risk for hypothyroidism is higher after radioactive iodine ablation despite the uptake suppression of her normal thyroid scan compared with a lobectomy. After an uncomplicated left lobectomy, her thyroid function remains normal with a TSH of 2.3 mIU/L.
Disclosure: Lee reports no relevant financial disclosures.