Drug-induced thyroiditis and papillary carcinoma in a minocycline-pigmented black thyroid gland

The Thyroid Pathologist Meets Therapeutic Pharmacology

The effects of many pharmacological agents on thyroid function are well known. Direct influences on measurements of thyroid function tests are also described. However, certain classes of drugs produce morphological changes in the gland. This review focuses on the significance of the following drug classes for the thyroid pathologist: iodine, antithyroid drugs, psychotropic drugs, antibiotics, cardiotropic drugs, antidiabetic drugs, and immunomodulatory agents. Radioactive iodine initially induces mild histologic changes; however, the long-term effects include marked follicular atrophy, fibrosis, and nuclear atypia-changes that vary depending on the pre-therapy condition of the gland. Some psychotropic drugs have been associated with a spectrum of inflammatory changes throughout the gland. The tetracycline class of antibiotics, namely minocycline, can lead to a grossly black thyroid gland with pigment seen in both colloid and follicular epithelial cells while variably present within thyroid nodules. The surgical pathologist most commonly sees an amiodarone-affected gland removed for hyperthyroidism, and the histologic findings again depend on the pre-therapy condition of the gland. While GLP-1 receptor agonists carry an FDA black box warning for patients with a personal or family history of multiple endocrine neoplasia or medullary thyroid carcinoma, the C cell hyperplasia originally noted in rats has not borne out in human studies. Finally, thyroiditis and hypothyroidism are well known complications of checkpoint inhibitor therapy, and rare cases of severe thyroiditis requiring urgent thyroidectomy have been reported with unique histologic findings. In this review, we describe the histologic findings for these drugs and more, in many cases including their functional consequences.

Urinary tetracycline antibiotics exposure during pregnancy and maternal thyroid hormone parameters: A repeated measures study

BACKGROUND

Studies on potential maternal thyrotoxicity related to tetracycline antibiotics exposure during pregnancy are lacking. Based on a large prospective cohort study, this study aimed to examine the associations between tetracycline antibiotics exposure in maternal urine and maternal thyroid hormone parameters.

METHODS

Based on the Ma'anshan Birth Cohort study, urine and serum samples of 2969 pregnant women were collected in the first, second and third trimesters. Tetracycline antibiotics, including oxytetracycline, chlorotetracycline, tetracycline and doxycycline in urine samples, as well as free thyroxine (FT4), thyroid stimulating hormone (TSH), total triiodothyronine (TT3) and total thyroxine (TT4) levels in serum samples, were measured. Linear mixed models and multivariate linear regression models were employed to examine associations between tetracycline antibiotics exposure during pregnancy and maternal thyroid hormone parameters.

RESULTS

The detection rates of four individual tetracycline antibiotics and all antibiotics (sum of four individual tetracycline antibiotics) in the three trimesters were 5.0%-52.3%, and the 95th percentile concentration ranged from 0.11 to 4.84 ng/mL. After adjusting for potential confounding factors, the repeated measures analyses indicated that pregnant women exposed to doxycycline and all antibiotics during the entire pregnancy were negatively associated with serum FT4 and TT4 levels but positively associated with serum TSH and TT3 levels. Trimester-stratified analyses found that doxycycline and all antibiotics exposure during the first trimester were negatively associated with serum FT4 and TT4 levels, while doxycycline was positively associated with TSH levels. In the third trimester, a significant association was only found between all antibiotics and TSH levels.

CONCLUSIONS

Our results suggest that exposure of pregnant women to tetracycline antibiotics is associated with maternal thyroid hormone parameters, and the first trimester might be the most critical window. More studies are needed to substantiate our findings and determine the underlying biological mechanisms.

Case Series: Minocycline-Associated Thyroiditis

INTRODUCTION

Minocycline, a member of the tetracycline class of antibiotics, has been associated with benign thyroid pigmentation but reports of thyroid dysfunction are sparse.

METHODS

Cases were selected via an inquiry of the electronic medical records for patients with thyroid dysfunction and the use of a tetracycline antibiotic. Non-autoimmune thyroiditis was defined as abnormally low or suppressed thyroid-stimulating hormone (TSH, <0.3 µIU/mL), elevated free thyroxine or total thyroxine, and undetectable antithyroid antibodies.

RESULTS

Nine cases of thyroiditis without autoimmunity were identified out of 423 reviewed patients. Cases of thyroiditis occurred in adolescents ages 14-17 years who had been taking minocycline for 6 months to 4 years. In all cases, minocycline was prescribed for the treatment of acne. Four of the 9 received treatment for thyrotoxicosis with a β-blocker (in 3 cases) and/or antithyroid drug (in 2 cases). Thyroiditis was symptomatic in all but one individual who presented with painless goiter. All thyroiditis was transient and resolved after a median of 4.5 months (range 2-5 months). In one case, thyroiditis was followed by transient hypothyroidism.

DISCUSSION

Minocycline is known to cause thyroid abnormalities, although it has not been definitively linked to thyroid dysfunction. Here, we report 9 cases of non-autoimmune thyroiditis in adolescents receiving minocycline for acne. We recommend that minocycline exposure be considered in the differential diagnosis for thyroiditis and that patients receiving minocycline be counseled regarding the risk of thyroid dysfunction.

Novel Cause of 'Black Thyroid': Intraoperative Use of Indocyanine Green

The antibiotic minocycline is virtually pathognomonic for brown-black discoloration of the thyroid gland referred to as 'black thyroid'. Black thyroid' is an incidental finding in patients taking the drug who undergo thyroid surgery for another indication and is not of known clinical significance. However, its recognition is important so as not to raise concern for a disease process. Here, we present the first case of 'black thyroid' attributable to the iodine-containing compound indocyanine green. Intraoperative indocyanine green was administered as part of a research protocol transoral robotic-assisted surgery for a base of tongue cancer in a 44-year-old man. Hemithyroidectomy was subsequently performed during the same operation for further evaluation of an indeterminate thyroid nodule. The resected thyroid lobe was dark, nearly black in color, and histologically showed extensive brown pigment deposition in the follicular epithelial cells and colloid, mimicking minocycline-induced 'black thyroid'. In this case, however, the patient was not taking minocycline; instead the 'black thyroid' was attributed to the iodine-containing compound indocyanine green. Indocyanine green is a hereto unreported cause of 'black thyroid' with histopathologic features that are remarkably similar to that induced by minocycline. Indocyanine green should be included the differential diagnosis of 'black thyroid'. Clinical history is important so as not to raise concern for a disease process.

Black thyroid associated with thyroid carcinoma

Objective. Black thyroid is a rare pigmented change seen almost exclusively in patients upon minocycline ingestion, and the process has previously been thought to be generally benign. There have been 61 reported cases of black thyroid. We are aware of 13 cases previously reported in association with thyroid carcinoma. This paper reports six patients with black thyroid pigmentation in association with thyroid carcinoma. Design. The medical records of six patients who were diagnosed with black thyroid syndrome, all of whom underwent thyroid surgery, were reviewed. Data on age, gender, race, preoperative fine needle aspiration biopsy (FNA), thyroid function levels, and pathology reports were collected. Main Outcome. The mean age was 60 years. There were 5 females, 4 of whom were African American. All patients were clinically and biochemically euthyroid. Black pigmentation was not diagnosed in preoperative FNA, and only one patient had a preoperative diagnosis of papillary thyroid carcinoma. The other patients underwent surgery and were found to have black pigmentation of the thyroid associated with carcinoma. Conclusions. FNA does not diagnose black thyroid, which is associated with thyroid carcinoma. Thyroid glands with black pigmentation deserve thorough pathologic examination, including several sections of each specimen.