Endocrine Abstracts

Introduction: IgG4-related thyroiditis (IgG4-RTD) is a rare fibroinflammatory disorder. It is characterized by dense lymphocyte infiltration (mainly IgG4+ plasma cells), enlargement and dysfunction of the thyroid gland. IgG4-RTD includes mostly cases of Hashimoto’s (HT) but also of Riedel’s and Graves’ thyroiditis. Diagnosis is set according to imaging and histopathological criteria. Papillary thyroid carcinoma (PTC) is the most common form of thyroid cancer (~90%). Co-occurrence of HT and PTC is found in 23-30% and the presence of HT is considered a favorable prognostic factor. The association between PTC and IgG4-RTD remains unclear. Metastatic PTC without an identifiable primary tumor is also a very rare phenomenon.

Case presentation: A 48-year-old woman attended our outpatient clinic presenting with progressive painless cervical enlargement and HT. The patient was euthyroid under levothyroxine treatment. Clinical examination revealed a diffusely enlarged, moderately hard thyroid and palpable, painless, mobile cervical lymph nodes. Neck ultrasonography showed diffuse thyroid enlargement with inhomogeneous, hypoechoic, hypovascular echostructure and several enlarged lymph nodes of the central and lateral cervical compartment. Cytological examination after fine needle aspiration of two suspicious nodes of the central compartment was suggestive of non-specific reactive lymphadenitis. Later, the patient presented further thyroid enlargement with marked stiffness, dysphagia and hoarseness. Thyroid core needle biopsy provided findings of the fibrosing variant of HT and IgG4-RTD. Serum IgG4 levels were also elevated. Computed tomography of chest, abdomen and retroperitoneum returned no findings of systemic IgG4-related disease. She was treated with methylprednisolone 16 mg/d and presented progressive clinical and imaging improvement. After surgical review, total thyroidectomy was carried out. Pathology report revealed HT with extended fibrosis at thyroid specimens and metastatic infiltration of follicular variant of PTC in two cervical lymph nodes. Post-op the patient received 50 mCi of I-131 for remnant ablation. Negative post-ablation whole body scan in conjunction with undetectable thyroglobulin levels and negative anti-thyroglobulin antibodies title were compatible with disease remission.

Discussion: IgG4-RTD, though an unusual clinical entity, should be considered in the differential diagnosis of thyroid enlargement. The management of a patient with IgG4-RTD and metastatic thyroid carcinoma without an identifiable primary tumor is rather challenging, as the impact of IgG4-RTD on cancer prognosis is still ambiguous. Failure in identifying primary tumor may be attributed to the small size (<3 mm) and/or the extended fibrosis of thyroid.