Fleas and Ticks: A Case of Simultaneous Diagnosis of Papillary Thyroid Cancer and Systemic Mastocytosis

Systemic mastocytosis is a clonal expansion of mast cells associated with an increased risk of solid malignancies. There is no known association with systemic mastocytosis and thyroid cancer. Herein, we report a young woman presenting with cervical lymphadenopathy and lytic bone lesions who was diagnosed with papillary thyroid cancer (PTC) and systemic mastocytosis simultaneously.

Case Description:

A 43-year-old woman presented with cervical lymphadenopathy for 3 weeks. She denied any fevers, night sweats, flushing, or skin rash. CT scan showed multiple bilateral enlarged cervical lymph nodes with bilateral thyroid nodules. Imaging also revealed many lytic lesions in her spine and pelvis. On physical examination, she had palpable cervical lymph nodes with a hard left-sided thyroid nodule. Neck ultrasound revealed a 2.1-cm left hypoechoic thyroid nodule with microcalcifications and cervical lymph nodes. Fine needle aspiration of the thyroid nodule and lymph nodes confirmed PTC. Patient underwent total thyroidectomy with bilateral central and lateral neck dissection, histology confirmed classic PTC (pT3N1bM0). Postsurgical serum thyroglobulin was 17.0 ng/mL and I131 scan showed no metabolic activity in axial skeleton. Subsequent bone marrow biopsy of the pelvic lytic lesions revealed systemic mastocytosis (>15 mast cells in aggregates, serum tryptase 52mcg/L (normal 2.2-13.2), KITD816V mutation, and one osteolytic lesion >2cm). Patient is treated with zoledronic acid 4mg IV every 3 months with improvement. Baseline DXA showed osteopenia.

Discussion:

PTC is an indolent malignancy with an excellent 10-year survival rate. Bone metastases are rare, occurring in < 4% of all thyroid cancers. Systemic mastocytosis is a proliferation of mast cells that has wide clinical spectrum from indolent disease to mast cell leukemia; symptoms may include flushing, nausea/vomiting, wheezing, allergic reactions, and in some cases anaphylaxis. The axial skeleton is affected in up to 50-70% of patients, resulting in focal osteosclerosis and osteolytic lesions. The most common malignancies known to be associated with systemic mastocytosis are melanoma and non-melanoma skin cancer.

In our patient, initial findings of multiple lytic lesions raised concern for thyroid cancer metastasizing to bones. However, there was no functional radiographic evidence of metastases. Correct diagnosis of concurrent systemic mastocytosis required bone biopsy. Our patient is currently doing well with a good prognosis for both conditions.