(14.06) Rapidly Growing Neck Mass Unraveled as Primary Thyroid Lymphoma

Primary thyroid lymphoma is a rare diagnosis and is defined as the presence of lymphoma involving the thyroid gland only or the thyroid gland and associated cervical lymph nodes only without evidence of local or distant disease at the time of diagnosis.

Case(s) Description :

A 75-year-old- female with a history of Myasthenia gravis was referred to the Endocrine clinic for evaluation of a rapidly growing neck mass. The patient reported symptoms of fever, neck pain, choking sensation, night sweats, and hoarseness associated with neck mass which progressively worsened in 2 weeks. She had a history of childhood radiation exposure from a shoe fluoroscope at the age of 10 years. Lab work showed normal thyroid function test. Initial CT soft tissue neck with contrast showed diffusely enlarged heterogeneous thyroid gland with multiple nodules and an associated mild stranding. Follow-up thyroid Ultrasound showed a diffusely enlarged and heterogeneous thyroid gland with several left-sided thyroid nodules. The dominant nodule was 3.4 cm, solid and hypoechoic. No enlarged lymph nodes were noted. Fine needle aspiration performed twice for the nodule was inconclusive.  Flow cytometry from thyroid biopsy tissue showed abnormal CD 10- positive B Cells (36%) but the tissue was insufficient to confirm diagnosis. It was followed by core thyroid biopsy which showed diffuse large B-cell lymphoma, germinal center B-cell-like immunophenotype with a high proliferation rate, 60 to 80% by Ki-67 index. Fluorescent In-Situ Hybridization (FISH) was negative for translocation of MYC, BCL2, or BCL6 with no evidence of an underlying low-grade lymphoma.  Bone marrow biopsy didn’t show any evidence of B cell lymphoma.  PET scan showed a very hypermetabolic lobulated mass measuring 6 x 9x 7 cm infiltrating the thyroid gland with no associated lymphadenopathy in the neck and no bone lesions noted.  With these morphological and immunohistochemistry findings, the patient was diagnosed with clinical stage 1E bulky ( >7.5 cm), germinal center B-Cell-like (GCB) diffuse large B-cell lymphoma (DLBCL). The patient received 6 cycles of R-CHOP (Rituximab- cyclophosphamide, Doxorubicin, vincristine, Prednisone) chemotherapy after consultation with oncology. The patient has been disease-free for 1 year.

Discussion :

Primary thyroid lymphoma is a rare entity accounting for around 5% of all thyroid malignant tumors. It should be considered in the differential diagnosis of rapidly enlarging neck mass.