Utility of Thyroglobulin measurement in fine-needle aspiration biopsy specimens of lymph nodes in the diagnosis of recurrent thyroid carcinoma

INTRODUCTION: The most common site for the metastasis of papillary carcinoma of the thyroid (PTC) is regional lymph nodes. Ultrasound (US) imaging may identify abnormal appearing lymph nodes, suspicious for PTC recurrence. Although fine needle aspiration biopsy (FNAB) of abnormal lymph nodes is often diagnostic of recurrence, small or cystic lymph nodes may be non-diagnostic due to lack of tumor cells. The measurement of thyroglobulin (TG) levels in FNAB specimens from lymph nodes suspicious for recurrent PTC can serve as an adjunct to the cytologic diagnosis. MATERIALS AND METHODS: 115 abnormal appearing lymph nodes were aspirated under ultrasound guidance in 89 patients with history of thyroid carcinoma. In addition to obtaining material for cytologic interpretation, an additional aspirate was obtained by FNAB and rinsed in 1 ml of normal saline for TG level measurements. RESULTS: The cytologic diagnoses included: 35 (30%) reactive lymph node, no tumor seen (NTS), 39 (34%) PTC, 23 (20%) inadequate for evaluation due to lack of lymphoid or epithelial cells (NDX) 15 (13%) atypical/suspicious for PTC, and 3 (3%) other (e.g. paraganglioma, poorly differentiated carcinoma and carcinoma not otherwise specified). TG levels were markedly elevated (median 312 ng/ml; normal < 10 ng/ml) in 28 (72%) cases of PTC lymph node recurrence identified on cytology. TG measurements were also elevated in 5 lymph nodes classified as NTS and 4 NDX on cytology which resulted in 5 and 3 carcinoma diagnoses respectively on histological follow-up. Of the 9 atypical/suspicious cases with elevated TG levels all resulted in carcinoma diagnoses on follow-up. CONCLUSION: The measurement of TG in FNAB specimens from lymph node in patients with history of PTC is useful in detecting recurrent disease, especially in cases when the specimen is known to be or likely to be inadequate for cytologic evaluation.