# Progressive Unilateral Proptosis and [ 18 F]FDG-Avid Lesions Connoting Aggressive Disease in Radioiodine-Refractory Differentiated Thyroid Carcinoma

## TL;DR

A patient with thyroid cancer that no longer responds to radioiodine developed aggressive disease shown by FDG scans and worsening symptoms.

## Contribution

Demonstrates the aggressive nature of FDG-avid lesions in radioiodine-refractory thyroid cancer through a clinical case.

## Key findings

- The patient developed orbital metastasis after radioiodine therapy, presenting as sudden unilateral proptosis.
- FDG-PET/CT showed more FDG-avid lesions than radioiodine-avid lesions, indicating aggressive disease progression.
- Despite targeted therapies, the disease progressed, highlighting the poor prognosis of FDG-avid RAIR-DTC.

## Abstract

Radioiodine-refractory differentiated thyroid carcinoma (RAIR-DTC) have poor prognosis as compared with radioiodine concentrating thyroid carcinoma. We present a case of follicular thyroid carcinoma presenting as a disseminated disease initially, underwent thyroid surgery and radioiodine (RAI) therapy. Following RAI, the patient developed a sudden-onset unilateral proptosis, finally diagnosed as orbital metastasis. [
18
F]-Fluorodeoxyglucose (FDG)-positron emission tomography-computed tomography identified FDG-avid metastatic lesions more numerous than the RAI-avid lesions. The patient was treated with local and systemic targeted therapy, but despite these treatments, he developed progressive disease indicating aggressive nature of the disease consistent with [
18
F]FDG-avid RAIR-DTC.