Introduction : We present a case of papillary thyroid cancer post thyroidectomy awaiting RAI Rx complicated with acute infectious mononucleosis (IM). An unusual presentation of IM triggered multimodality imaging by various specialists. Confounding results of imaging studies created a diagnostic dilemma. This case highlights how a concomitant inflammatory / infectious disease can make management of both thyroid cancer and concomitant illness challenging.
Case(s) Description : 59-year-old female underwent total thyroidectomy for thyroid cancer on 12/28/2022. Surgical pathology showed papillary carcinoma, follicular variant, measuring 5.5 cm in the left and 0.5 cm in the right thyroid lobe (PT category: pT3a). Presented to ED a week later with left sided abdominal pain, fever, and chills. Labs consistent with infectious mononucleosis (IM). CT abdomen with contrast in ED showed a 2.4 cm omental enhancing nodule in the LLQ (concerning for metastasis) and bilateral 2-3 mm lower lobe lung nodules. CT guided biopsy of the omental mass on 2/7/23 was inconclusive. CT chest with contrast ordered by PCP the following week showed mediastinal and hilar adenopathy measuring up to 2.2 cm and small left lower lobe pulmonary nodules. Metastatic disease was in the differential diagnosis. Acute onset diplopia due to right sixth (abducens) nerve palsy in mid-January 2023, a rare complication of IM, created further concerns for the patient awaiting RAI Rx.
An oncologist felt that although CT imaging findings could be due to IM, thyroid cancer metastasis could not be conclusively excluded. A subsequent PET/CT showed evidence of thyroidectomy with low-level activity throughout the thyroid bed. Multiple areas of low-level nonspecific activity were noted in the subcarinal region, with bilateral hilar, mediastinal, pelvic and cervical lymph nodes. As per the radiologist well-differentiated thyroid metastatic disease was in the differential diagnosis. Mild splenic and marrow activity was however suggestive of ongoing inflammatory processes. As patient had received iodine contrast for CT scans an Iodine131 whole body scan was not an option at that time. The RAI Rx for thyroid cancer also had to be postponed.
3.5 months later while patient was off levothyroxine replacement in preparation for RAI Rx and TSH was 67, the thyroglobulin level of 2.4 ng/ml (anti-TGB antibody < 1) did not suggest significant residual thyroid tissue. Patient received RAI Rx for thyroid cancer (154.6 mci I-131) on 4/19/2023. Post RAI Rx whole body scan revealed no definite evidence of metastasis.
Discussion : Work up for inflammatory / infectious illnesses in thyroid cancer patients with suspicious imaging studies along with care coordination among specialists and PCP can help avoid delay in treatment, minimize diagnostic procedures and ease patient anxiety during a challenging time.
