Sarcoidosis mimicking metastatic thyroid cancer following radioactive iodine therapy

INTRODUCTION Sarcoidosis is an inflammatory disease characterized by non-caseating granulomas that can be present in diverse organ systems. Sarcoidosis can be associated with malignancy, presenting either preceding, during, or after chemotherapy. We herewith report a case of sarcoidosis mimicking cancer recurrence that developed after radioactive iodine therapy for papillary thyroid cancer. BACKGROUND A 68-year-old Caucasian woman was found to have an incidental mediastinal lymph node. She underwent biopsy, which revealed sarcoidosis. There was no further treatment or evidence of recurrence over the ensuing 9 years. She was then diagnosed with low-grade papillary thyroid cancer in the right posterior lobe and treated with total thyroidectomy followed by radioactive iodine therapy. Six months later, she was found to have elevated serum thyroglobulin. Post-remnant ablation scan showed increased tracer uptake in the bed of the thyroid. Though two thyroid ultrasound scans were negative, she was treated with I-131 for possible recurrence. She then developed right hip pain, prompting further investigation. Though a skeletal survey was negative, an 18-fluorodeoxyglucose positron emission tomography (PET) scan study revealed multiple hypermetabolic skeletal lesions in both humeri and the proximal left femur. In addition, hypermetabolic hilar and mediastinal nodes were noted. As widespread cancer metastasis was suspected, bone biopsy was performed, which showed non-caseating granulomas, consistent with recurrence of sarcoidosis. CONCLUSION Sarcoid lesions may mimic metastatic disease or recurrence in oncologic patients. Biopsy and histopathology examination should be performed to confirm the diagnosis. Recurrence or reactivation of sarcoidosis has been proposed to result from altered immunologic milieu because of the presence of either active cancer or its therapy. Teodorovic and colleagues postulated that the radioactive I-131 therapy leads to reduced secretion of Th2 cytokines such as interleukin (IL)-4, IL-5, and IL-13. Few case reports of sarcoidosis associated with papillary carcinoma have been published; this is the first report of systemic recurrence of sarcoidosis associated with papillary thyroid carcinoma after treatment with radioactive iodine therapy.