Extra-nodal marginal zone mucosa-associated lymphoid tissue thyroid lymphoma (MALT) has an indolent course, associated with long-standing autoimmune Hashimoto’s thyroiditis. There are still challenges in diagnosis of this type of thyroid tumor as its indolent behavior and the cytological and histological similarities with Hashimoto’s thyroiditis. We present a case of a 70-years-old woman with thyroid MALT lymphoma mimicked subacute painful thyroiditis.

A clinical course and investigations of this case has been described.

A 70-year-old Thai woman with a history of long-standing hypothyroid Hashimoto’s thyroiditis requiring levothyroxine 100 µg/day for more than 3 decades presented with anterior neck pain with enlarging thyroid goiter for 1 week. She had no signs of fever or a preceding infection of the upper respiratory tract. Six months earlier, thyroid ultrasonography (US) was done as a part of health screening. A large complex solid-cystic nodule 3.9x5.8x6.8 cm occupying right lobe of thyroid gland with multiple enlarged right cervical lymph nodes (LNs) up to 1.7 cm were found. Core needle biopsy showed dense small-lymphocytic proliferation without malignancy. The patient was advised to regularly follow-up. Subacute painful thyroiditis was diagnosed in this visit based on clinical examination and elevated erythrocyte sedimentation rate (ESR) at 80 mm/hour. Oral prednisolone 30 mg/day was given and she responded very well with relieving her neck pain and reduced the goiter size. However, the recurrent episodes swollen and painful neck were developed when oral prednisolone was tapered less than 10 mg/day. Over the course of 24 months, the patient had been continued oral prednisolone continuously varied in the dose of 5-20 mg/day. Eventually, US thyroid was done again at 30 months from the initial US. A large well-defined inhomogeneous hypoechoic mass occupying entire right thyroid lobe with multiple cervical LNs were found. Core needle biopsy at both right thyroid nodule and cervical LNs were done again with immunohistochemistry staining. The findings were suggestive of MALT thyroid lymphoma. Further investigations revealed no distant dissemination. The patient underwent watchful waiting for 6 months but relapse disease developed requiring chemotherapy. She is doing well at 18 months after the diagnosis.

Patients with known Hashimoto’s thyroiditis with rapidly enlarging neck mass should raise suspicion for thyroid tumors. Primary thyroid lymphoma especially low-grade MALT lymphoma is still challenges in diagnosis and painful thyroid mimicked subacute thyroiditis could be its manifestation.