Thyroid Bed Lymphadenopathy After COVID-19 Vaccine in a Patient with History of Thyroidectomy Due to Hurthle Cell Thyroid Cancer

The primary treatment for differentiated thyroid cancer is surgical resection with or without postoperative radioactive iodine ablation with I-131, depending on the risk stratification. Despite the good prognosis, local recurrence and distant metastasis are not uncommon. Hence these patients need to be monitored closely with neck ultrasound, thyroglobulin, and thyroglobulin antibodies. Cases of LAD caused by the COVID-19 vaccine have been reported. Common LAD sites are the ipsilateral axilla and supraclavicular lymph nodes (LN) and, less commonly, the cervical LN.

Case Description:

44-year-old-female with h/o Stage I Hurthle cell carcinoma, status post complete thyroidectomy. Neck ultrasound (US) had shown no recurrence of the disease until 6/9/2021 when her routine follow-up ultrasound showed bilateral hypoechoic and cystic lymph nodes highly suspicious for metastatic lymphadenopathy. CT of the neck with contrast confirmed findings.

The patient had recently received her COVID-19 vaccine in March 2021. She underwent a fine needle and core biopsy of the right cervical LN. Cytology was negative for metastatic carcinoma, and flow cytometry was negative for lymphoma.

A repeat neck ultrasound on 11/4/21 showed complete resolution of the abnormal right-sided lymph nodes and significantly smaller left-sided lymph nodes.

Discussion:

Differentiated thyroid cancer has a relatively good prognosis compared with other malignancies.

Lymph node involvement is common in papillary and Hürthle cell cancers. Despite the good prognosis, distal metastasis and local recurrence are relatively common. Hence these patients need to be monitored closely with neck ultrasound. Identification of LN on follow-up ultrasound should be interpreted with caution as other conditions could cause cervical LAD not related to cancer recurrence.

There have been case reports of LAD following the COVID-19 vaccine. Common LAD sites are the ipsilateral axilla and supraclavicular LN and, less commonly, the cervical LN. LAD can persist for up to 6 weeks, but there have been case reports where LAD lasted for over six weeks. US lymph node characteristics most consistent with malignancy are a cystic appearance, microcalcifications, loss of the normal fatty hilum, peripheral vascularization, a rounded rather than oval shape, hyperechogenicity.

Knowledge of the different LN characteristics can help differentiate a benign from a malignant LN in patients with a history of cancer. This can help avoid unnecessary workup and overtreatment. Though the presence of cystic LN had a specificity of 100% in one study, this was not the case with our patient whose biopsy was negative for malignancy. This emphasizes that in some cases like our patient, a biopsy is needed and is the only way to rule out the presence of malignancy certainly. It may be reasonable to obtain imaging studies before administering the COVID-19 vaccine in patients with cancer history and risk of LN metastasis to differentiate LAD caused by the vaccine versus malignancy.

Recurrence of thyroid cancer was ruled out with a negative biopsy result, so the COVID-19 vaccine was felt to be the most likely cause of the cervical LAD.