Thyroid metastasis from renal cell carcinoma presenting as a solid mass with rapid enlargement.

Summary: Thyroid metastases from nonthyroidal malignancies (NTMs) represent a diagnostic challenge, often displaying heterogeneous clinical manifestations. These metastases are rare but significant, accounting for approximately 2% of thyroid malignancies. Distinguishing them from primary thyroid malignancies is challenging due to the lack of specific ultrasound features, and the ultrasound-based risk stratification systems offer limited utility in such cases. Fine needle aspiration cytology is crucial for definitive diagnosis, yet it may not always provide accurate results. In this case report, we describe a unique instance of thyroid metastases originating from renal cell carcinoma, emphasizing the complexities in diagnosis and the importance of considering oncological conditions when assessing thyroid masses. Awareness of thyroid metastasis from NTMs, particularly in cases of diffuse thyroid hypoechogenicity and hypothyroidism, is essential for clinicians in their diagnostic approach. Learning points: Thyroid metastases from nonthyroidal malignancies are diagnostic challenges due to their heterogeneous clinical presentations, often mimicking primary thyroid malignancies. Thyroid metastases from nonthyroidal malignancies are relatively rare, but they still account for approximately 2% of thyroid malignancies. It is fundamental to consider oncological conditions when assessing thyroid masses, especially in cases of diffuse thyroid hypoechogenicity, hypothyroidism, and history of other tumors. Thyroid presentation is quite similar to that of autoimmune hypothyroidism, endocrinologists must be aware of the possibility of thyroid hypofunction due to the massive invasion of the parenchyma.

Macro-TSH: An Uncommon Explanation for Persistent TSH Elevation That Thyroidologists Have to Keep in Mind.

A macro-thyroid-stimulating hormone (macro-TSH) is an infrequent yet noteworthy phenomenon in the thyroid field. A 69-year-old patient presented with persistently elevated thyroid-stimulating hormone (TSH) levels ranging from 30 to 50 mIU/L, paradoxically accompanied by normal thyroid hormone levels and normal thyroid ultrasound, with no findings on pituitary magnetic resonance. Laboratory studies were conducted to investigate potential interferences impacting the accuracy of TSH measurements. After excluding other potential causes, polyethylene glycol (PEG) precipitation technique was used, which led us to the diagnosis of macro-TSH. This result was confirmed through chromatography. Macro-TSH, although rare, emerged as the key contributor to the patient's unexplained increase in TSH levels. This case highlights the importance of considering macro-TSH as a potential etiology in cases characterized by unexplained TSH elevation, offering insights into diagnostic protocols and expanding our understanding of thyroid function anomalies.