Ultrasound is the imaging modality of choice for the evaluation of the thyroid and the risk stratification/follow up of thyroid nodules. Many different proposals of a Thyroid Imaging Reporting and Data System (TIRADS) have been described in the literature. For the description of thyroid nodules in our hospital, we adhere to the system as proposed by Kwak et al. [11]
Regardless of the TIRADS system used, several described sonographic features are nearly universal. Lesions that are mainly solid are more suspicious than lesions that are mixed or predominantly cystic. The echogenicity of the solid part is also an important marker: lesions that are hypoechoic or even markedly hypoechoic (as compared to the strap muscles) are also associated with higher incidence of thyroid cancer. The lesions contours can be smooth (low suspicion) or irregular (high suspicion). Two other criteria are often used and are, though less common, more specifically associated with malignancy: taller-than-wide aspect and microcalcifications. Taller-than-wide refers to nodules that are more likely to extend to the depth of the thyroid on the axial images. Microcalcifications are, unlike macrocalcifications, difficult to detect on ultrasound. Any combination of these 5 signs leads to an increased probability of thyroid malignancy. In the described case, all different signs were present, suggesting a high statistical probability of thyroid cancer.
The literature considers sclerotherapy to be a safe and effective treatment for benign thyroid cysts. No subsequent diagnostic problems were reported as a complication. It could be we witnessed a common but underreported effect due to small patient groups and lack of follow-up. If this is the case, patients who have undergone sclerotherapy may then be at risk of false-positively being diagnosed with thyroid malignancy if the relevant medical history is not considered. As sclerotherapy is usually performed with ethanol, it can also be suggested that doxycycline is specifically the agent to blame in this case. Systemic use of doxycycline is known to sometimes cause a non-immune chemical thyroiditis [12], dubbed as black thyroid due to the intense black discoloration of the thyroid [13]. It might be that the instillation of doxycycline was responsible for a similar, more localized, process of affliction.
In conclusion we would suggest that for the work-out of a solitary suspicious thyroid lesion, the medical history of the patient should always be considered. In case of antecedents of ipsilateral sclerotherapy, a reactive inflammatory response may mimic thyroid malignancy. In this specific case Doxycycline was responsible, an effect that may specifically be explained by the occurrence of non-immune chemical thyroiditis. It is not known if other sclerosants may elicit the same effect. A fine needle aspiration should be performed to exclude thyroid cancer. Treatment is not necessary; the affliction appears self-limiting as evidenced in the follow-up of this case.