Why is TSH suppression so often the sole or primary goal in thyroid cancer treatment with little regard for Quality of Life (QoL)?
We are told, over and over, that the vast majority of thyroid cancer patients do just fine for the rest of their lives on synthetic thyroid hormone replacement (THR) therapy evaluated by monitoring TSH. Yet we see on the thyroid cancer forums and groups that patients experience symptoms of both over and under medication, may be prescribed secondary drugs to counter the symptoms of inappropriate medication levels, and often have their symptoms and concerns dismissed. These impressions have been supported by QoL research.
Suppressive dosages of levothyroxine (T4) may trigger anxiety, irritability, mood swings and tachycardia or atrial fibrillation – symptoms common to “hyperthyroidism”. If the dosage is lowered to alleviate these symptoms, TSH may respond by remaining high or increasing which can stimulate growth of any remaining thyroid tissue or cells.
At the same time, the level of circulating thyroxine (T4) may not be converted sufficiently to the biologically active triiodothyronine (T3) hormone. It is this active T3 hormone which affects every function in the body. If levels are inadequate patients will experience symptoms common with “hypothyroidism” — fatigue, inability to remain focused, other symptoms lumped together as “brain fog”, trouble acomplishing necessary activities of daily living, hair loss.
Symptoms of both over and under medication may be experienced at the same time – one forum moderator has coined the phrase “Wired and Tired”. When patients share their lab reports what frequently shows up is free T4 in the upper reaches of or above the lab reference range together with free T3 at or below the lower end of the range. They have been told there is no reason to review or change their THR therapy as their levels are “normal”, i.e. within the laboratory reference range, and any symptoms must be from some other cause. This is seen even when continued increases of levothyroxine fail to suppress TSH to desired levels.
While it is true that other factors may affect how an individual responds to their THR therapy, refusing to test for free T4 and free T3 and evaluate the balance of thyroid hormone levels in the context of the synptoms the patient is experiencing can result in prolonged and needless poor health. Judging by the results of the large North American Thyroid Cancer Survivorship Study . Adverse consequences of thyroid cancer treatment experienced by patients were dramatically higher than reported by physicians.
Based on the paucity of literature on thyroid cancer survivorship, it seems that long-term survival for patients with thyroid cancer has been perceived in the past as a relatively benign experience, particularly when compared with survivors of other cancers. This perception is likely because thyroid cancer has a good five-year survival rate. The current findings from the NATCSS illustrate that this perception is unfounded, and that thyroid cancer survivors experience several adverse physical, psychological, social, and spiritual challenges that linger for many years following treatment.
Historically the advent of synthetic hormone replacement radically changed treatment of thyroid dysfunction, whether spontaneous, medically or surgically induced. Instead of treating symptoms, treatment shifted to treating the numbers, or lab results. TSH was heralded as the gold standard indicator for “euthyroidism” or what was considered “normal” thyroid function. This gave practitioners carte blanche to inform the patient that their symptoms couldn’t possibly be related to thyroid hormone dosing or levels.
Thyroid receptors aren’t equal throughout the body — some organs and tissue have a greater or lesser affinity for T3 than others, and various tissue and cell types convert T4 to T3 at diffeerent rates than others. Just as “one size fits all” doesn’t work for shoes, it doesn’t work for dissimilar organs and muscles. As we don’t have a convenient or cost effective way to measure tissue levels of T3 – the truest measure of thyroid function or response to THR therapy – we use the more convenient free T3 (free triiodothyronine) test as a proxy.
Free T3 levels can be influenced by several factors including general health or illness, exercise, dietary deficiencies or co-morbidities. Many of these are well known but are used as an excuse to exclude free T3 testing. Instead, tertiary factors need to be evaluated and either ruled out or treated concurrently instead of being brushed off as inconsequential.
Other reasons put forward to exclude free T3 level testing — short half life producing peaks and valleys or circadian variance in levels — are no more valid than monitoring any medication with a short active half life. In addition, though T3 has a rapid onset, triiodothyronine achieves a steady state in approximately 2-1/2 to 3 days.
For thyroid cancer patients, keeping TSH levels low or suppressed may reduce the risk of recurrence. The HPT-axis is sensitive to both T4 and T3 circulating levels and, when appropriately balanced, liothyronine (T3) is an important addition to supporting both TSH suppression and Quality of Life.
Risk Factors for Decreased Quality of Life in Thyroid Cancer Survivors: Initial Findings from the North American Thyroid Cancer Survivorship Study
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4684649/
Pharmacokinetics of L-Triiodothyronine in Patients Undergoing Thyroid Hormone Therapy Withdrawal
https://pubmed.ncbi.nlm.nih.gov/31364488/
Physiology, Thyroid Stimulating Hormone
https://www.ncbi.nlm.nih.gov/books/NBK499850/
Quick Thyroid Tour – the HPT Axis
Thyroid Cancer Advocates 