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, hypoechoic or even markedly hypoechoic are more suspicious than lesions that are mixed or predominantly cystic. Lesion contours, taller-than-wide aspect and microcalcifications are other remaining factors that should be considered.

The literature considers sclerotherapy to be a safe and effective treatment for benign thyroid cysts. Sclerotherapy is almost exclusively performed by percutaneous ethanol injection (PEI), the safety of this procedure has been well established since the introduction of the technique in 1990 by Livraghi et al. [12] These authors followed 101 patients over the course of 4 years to evaluate the long-term efficacy of their proposed treatment.

A large clinical trial on the use of PEI was subsequently conducted by Lee et al. [13] and included 654 patients. Not only did these authors opt to treat thyroid cysts, but they treated solid nodules as well. Complete response, partial response and no response were found to be 17.2%, 71.7%, 11.1% in solid nodules as compared to 19.0%, 60.4%, 20.6% for complex cysts, respectively.

Minimally invasive treatment of symptomatic thyroid nodules has since become commonplace. Therefore, the Task Force Committee of the Korean Society of Thyroid Radiology initiated a consensus statement providing recommendations for the role of PEI in the management of symptomatic thyroid nodules [14]. These guidelines consider different known complications of sclerotherapy, such as localized pain, hematoma, facial flushing, drunken sense, hoarseness, dyspnea, and temporary hyperthyroidism. In malignant cases, tumor implantation can occur as a very rare complication that can occur months to years after PEI [15].

The patient described in this report was also treated for a benign thyroid cyst, with doxycycline as a sclerosing agent. None of the aforementioned complications was present in our case, however a routine follow-up one year later found a large suspicious lesion present in the treated region of the thyroid. Considering the timeframe, the localization of this lesion and the inflammatory cells found in the fine needle aspirate, it seems logical to consider a link to the prior treatment. No other case can be found in the literature in which a diagnostic problem arose after PEI treatment of a thyroid cyst, nor in those few studies where different sclerosing agents were used.

It could be we witnessed a common but underreported effect of thyroid sclerotherapy in general, due to small patient groups and lack of follow-up. If this is the case, patients who have undergone sclerotherapy might be at risk of false-positively being diagnosed with thyroid malignancy if the relevant medical history is not considered. The aforementioned study by Lee et al. [13] however included 654 patients who were followed up for 36 months after PEI treatment and did not report on any suchcomplications.

As sclerotherapy is usually performed with ethanol, it can then 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 [16], dubbed as black thyroid due to the intense black discoloration of the thyroid [17]. It might be that the instillation of doxycycline was responsible for a similar, more localizedarea of thyroiditis.

In conclusion we would suggest that for the work-up 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, however this complication was not reported in large follow-up studies that use ethanol as sclerosing agent. It could however be that these inflammatory changes post sclerotherapy have not been reported as this may be thought of by different authors as a normal process. 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.