From Inconclusive Fine Needle Aspiration to Double Malignancies: A Case Report of Primary Thyroid Lymphoma With Concurrent Papillary Thyroid Carcinoma in a Sickle Cell Disease Patient in Saudi Arabia

Primary thyroid lymphoma (PTL) is considered a rare and aggressive form of malignancy. Reaching a diagnosis might be challenging due to the diverse clinical and histopathological presentation and inconclusive cytology, especially in patients diagnosed with Hashimoto's thyroiditis, as results may be affected by the chronic inflammatory changes. The simultaneous existence of PTL with papillary thyroid microcarcinoma is relatively rare, as indicated by the current literature and reported cases worldwide and locally. A 45-year-old woman with hypothyroidism and sickle cell disease (SCD) presented initially with an incidental nodule found on routine ultrasound. Initial fine needle aspiration (FNA) was suggestive of Hashimoto's thyroiditis, and the patient underwent serial monitoring in the outpatient department (OPD), which subsequently revealed an extensively growing neck mass. Due to rapid evolution and increasing mass symptoms, the endocrine surgery team performed a total thyroid gland removal. Post-resection thyroid tissue histopathology revealed the presence of high-grade B-cell lymphoma involving both lobes and an incidental occurrence of papillary thyroid carcinoma (PTC). The patient tolerated chemotherapy with continued surveillance and observation. Post-chemotherapy computed tomography positron emission tomography (PET-CT) scan demonstrated a new lesion with increased uptake of F-fluorodeoxyglucose (FDG) near the thyroid, following postoperative anatomical changes, which initially appeared representative of relapse. Nonetheless, a surgical biopsy demonstrated benign lymphoid hyperplasia, and the patient remains in remission. This case exemplifies the potential limitations of FNA in PTL, the diagnostic challenge of double malignancies, and the importance of histological validation for PET-positive lesions in continuous OPD follow-up and surveillance.