A couple of weeks ago, I stumbled upon a doctor online (LeoMedicina) who makes educational videos on TikTok and Youtube designed to help pre-med/medical students prepare for structured training programs that cover core specialties in medicine like surgery, pediatrics, and internal medicine. One of their videos that caught my attention spoke on hypothyroidism.
So...what is Hypothyroidism?
Hypothyroidism, also known as underactive thyroid, is what happens when there is not enough production of the thyroid hormone within the thyroid gland. The thyroid gland, located at the base of the neck, is responsible of making two hormones that affect every cell, support how the body uses fats and carbohydrates, control temperature, heart rate, and protein production; these hormone are called thyroxine and triiodothyronine.
Common Causes & Symptoms
The most common causes for hypothyroidism are Hashimoto disease, an autoimmune disease where immune system makes antibodies that attack healthy thyroid tissue, radiation therapy for head and neck cancers, and pituitary condition where pituitary fails to make enough thyroid stimulating hormone.
The symptoms vary and depend on the severity of the condition and how they develop slowly over years. Some of the symptoms include: tiredness, more sensitivity to cold, constipation, dry skin, weight gain, etc. Early symptoms of hypothyroidism like fatigue and weight gain are easy to dismiss as stress or getting older. The more metabolism continues to slow down, the more the symptoms emerge.
A recent 2026 case report in Frontiers in Psychiatry described severe hypothyroidism during pembrolizumab therapy to be presented as hyperactive delirium with symptoms like hallucinations and confusion.
Closing
If you ever feel tired for no reason or tend to notice several of the symptoms that were previously mentioned, a simple blood test/TSH test can be taken to be clinically diagnosed for hypothyroidism. Once dosage is optimized, thyroid hormone replacement is the correct treatment for this.
Fregolente, E. V., Buhler, S., & Lahr, J. (n.d.). Frontiers in Psychiatry. Case Report: Hyperactive Delirium with Psychotic Symptoms associated with severe hypothyroidism during pembrolizumab therapy. Complete Remission after Levothyroxine and no Recurrence after Rechallenge to Pembrolizumab. https://www.frontiersin.org/journals/psychiatry/articles/10.3389/fpsyt.2026.1905725/abstract
Hypothyroidism (underactive thyroid) - Symptoms and causes. (2026, September 10). Mayo Clinic. Retrieved October 5, 2026, from https://www.mayoclinic.org/diseases-conditions/hypothyroidism/symptoms-causes/syc-20350284
Journal of Oral Rehabilitation. (n.d.). Assessment of Salivary Glands in Hypothyroid Patients Utilising Clinical, Ultrasonographic, and Elastographic Techniques, 53(6), 1091-1104.
Springer Nature Link. (n.d.). Differential association of hypothyroidism with cardiovascular events and cardiovascular mortality: a systematic review and meta-analysis, 91.
Zhao, T., Zhang, N., Tian, Y., & Yang, Z. (n.d.). Frontiers of Psychiatry. Thyroid hormone replacement is associated with improvement in renal dysfunction in patients with hypothyroidism: a retrospective observational study, 17.
This was incredibly interesting! I was particularly interested in the connection of pembrolizumab to hypothyroidism because pembrolizumab is an immune checkpoint inhibitor. It's fascinating how it sets the immune system into overdrive to attack the cancer but, the collateral damage can be to the endocrine system including the thyroid. I also learned that in the diagnostic process, it’s generally best to check TSH along with free T4 because TSH alone might not tell the whole story for some. Do you think patients receiving medications like pembrolizumab should have their thyroid hormone levels checked regularly even before symptoms such as fatigue, weight gain, or confusion appear?
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