What are hot and cold thyroid nodules?

Thyroid nodules are usually benign (non-cancerous) tumors which are very common in clinical practice. They develop from excessive thyroid cell replication. In adults above the age of 60 thyroid nodules can be found in more than 50% of the population1.

1Laszlo Hegedus M.D, The thyroid nodule, 2004.

The different types of thyroid nodules

Nodules which are small in size and located some distance from sensitive structures such as the trachea are often asymptomatic (meaning patients don’t feel them and they cause no health issues), they may not even be noticed. Nevertheless, some thyroid nodules can cause symptoms like shortness of breath or – only in the case of hot nodules – hyperthyroidism (overactive thyroid2).
Benign nodules are classified based on their ability to produce hormone in comparison to healthy thyroid tissue. They are differentiated into three categories: hot, cold and indifferent (or “normal”) nodules. Hot nodules are more active than regular thyroid tissue and therefore produce more hormones in comparison. On the other hand, cold nodules are lumps of tissue without any real ability to produce thyroid hormones compared to regular thyroid tissue. Lastly, normal or indifferent nodules cannot be differentiated from healthy tissue based on their hormone producing ability. Most thyroid nodules are cold nodules (approx. 50-85%), whilst only 10% of nodules are “hot” and about 40% are indifferent3.

2Sy Kraft, What are thyroid nodules?, 2018.
3Markus Eszlinger and Laszlo Hegedüs, Molecular diagnosis of indeterminate thyroid nodule FNA cytology results, 2017.

Symptoms of cold and indifferent nodules

Cold and indifferent nodules are often asymptomatic due to their size, small enough not to be seen without imaging tests. In the US, only 4-7% of the adult population have palpable lumps, whereas detectable lumps, found with ultrasound, occur in more than 50% of the population above the age of 60. Nevertheless, if cold and indifferent nodules grow they can cause discomfort and problematic symptoms by exerting pressure on sensitive structures in the neck. Commonly reported symptoms in those cases include a feeling of compression, voice changes as well as difficulty breathing or swallowing.

Symptoms of hot nodules

Due to their increased hormone producing ability, hot nodules can cause significant metabolic imbalance and dysregulation of various processes in the body. As long as these nodules remain small effects may not be serious, however, excessive hormone overproduction can lead to the development of hyperthyroidism. Symptoms of hyperthyroidism include anxiety, restlessness, tremors, agitation, sweating, unusual weight loss and increased heart rate amongst others. In extreme cases, the effects of disease can even become life-threatening. Especially amongst, older people who are at risk of experiencing irregular heart rhythms and even heart failure in cases of extreme and untreated hyperthyroidism4.

4Ignac Fogelman, The Bone and Mineral Manual (Second Edition), 2005.

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Diagnosis and treatment of different types of thyroid nodules

Despite the vast majority of lumps in the thyroid being non-cancerous, early diagnosis is of high importance to clearly classify a nodule and rule out any risks of malignancy. Moreover, diagnostic tools help to recognize different types of nodules (hot, cold or indifferent) in order to decide upon the most suitable treatment regimen. A scintigraphy (nuclear thyroid scan) is a commonly used tool to classify thyroid nodules5.
Various treatment options are available. Whilst surgical excision and radioactive iodine treatment are still common and remain the gold standard for cancer, less invasive treatment methods are available for non-cancerous lumps. These include minimal-invasive thermal ablation options such as laser ablation, microwave ablation (MWA) or radiofrequency ablation (RFA) as well as the non-invasive Echotherapy.

5Ibid.

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