Sonographic changes in the thyroid gland after sclerotherapy with doxycycline can be mistaken for thyroid cancer

Background The literature considers sclerotherapy to be a safe and effective treatment for benign thyroid cysts. No subsequent diagnostic problems have been reported as a complication. We report the occurrence of focal inflammation after said therapy, mimicking a thyroid malignancy. Case presentation We report a case of a young male with a solitary strongly suspicious lesion in the thyroid. The patient had undergone prior sclerotherapy of a thyroid cyst with Doxycycline. The lesion appeared to be a focal area of inflammation and thus iatrogenic in nature. Systemic use of doxycycline is known to sometimes cause a non-immune chemical thyroiditis, dubbed as black thyroid due to the intense black discoloration of the thyroid. It might be that the instillation of doxycycline was responsible for a similar, more localized area of thyroiditis. Conclusions For the work-up of a solitary suspicious thyroid lesion, the medical history of the patient should always be considered. In case of prior ipsilateral sclerotherapy, a reactive inflammatory response may mimic thyroid malignancy. A fine needle aspiration should be performed to exclude thyroid cancer. Treatment is not necessary; the process appears to be self-limiting as evidenced in the follow-up of this case.