Pediatric differentiated thyroid carcinoma leading to fatal lung fibrosis.

Introduction: This case report aims to discuss the development of fatal lung fibrosis in a young boy following treatment of metastasized differentiated thyroid carcinoma (DTC). Case presentation: A 3.6-year-old boy was diagnosed in year 1995 with papillary thyroid carcinoma with extensive metastases. He underwent total thyroidectomy and received multiple courses of radioactive iodine (RAI) therapy between September 1995 and February 1998. The patient received six courses of RAI therapy within 30 months, cumulatively amounting to 10 GBq 131I, in response to significantly elevated thyroglobulin levels and morphologically persistent miliary lung metastases. Despite the significant regression of his metastatic disease, the patient exhibited progressive lung fibrosis 2.75 years after the sixth RAI therapy. This condition ultimately led to respiratory failure and resulted in the patient's death 6.7 years following the initial diagnosis. Discussion/conclusion: This case highlights the potential severe complications associated with several courses of RAI therapy in young children suffering from extensive lung metastases and underscores the need for careful treatment planning and long-term monitoring. Given the risks of RAI therapy, particularly the risk of fatal lung fibrosis, it is crucial to tailor RAI therapy carefully, especially in young patients. Notably, thyroglobulin levels can decrease even after cessation of RAI therapy, indicating that levels immediately post-therapy are not necessarily representing the development of the response over the following months.