Unexplained Weight Loss with Normal Thyroid Levels: Possible Causes

Significant weight loss with normal thyroid function tests?

Hello Dr.
Lee,
In early November last year, during my health check-up, my height and weight were 181 cm and 58.7 kg, respectively.
Aside from being underweight, all other indices were normal (including CEA and fecal occult blood).
However, by the end of April this year, my weight had decreased to 57.8 kg.
Due to my weight continuously declining over the past few years, I began to worry about whether I have any underlying health issues, and I have become extremely anxious.
As a result, in the past two weeks, my weight has dropped another 2 kg.
I have a history of mitral valve prolapse, and I experience noticeable tremors when I hold my arms up.
Recently, I have also been experiencing palpitations, rapid heart rate, and chronic diarrhea (normal frequency, but stools are often unformed).
After consulting with my doctor, hyperthyroidism was suspected, and I underwent blood tests.
However, the recent lab results showed T3: 1.12 ng/mL, TSH: 0.5180 µIU/mL, and Free T4: 1.18 ng/dL, all of which appear to be within normal ranges.
Therefore, I would like to ask if this can completely rule out hyperthyroidism as the cause of my weight loss.
If it can be ruled out, what other diseases could potentially be causing my weight loss? I am particularly concerned about the possibility of cancer, but my doctor mentioned that it is unlikely given my age.
Could it be autonomic nervous system dysfunction? Thank you.

Jerry, 20~29 year old female. Ask Date: 2022/05/11

Dr. Li Jian reply Internal Medicine

If thyroid function is normal, it may be advisable to consult a gastroenterologist to investigate whether the weight loss is related to chronic diarrhea.

Reply Date: 2022/05/11

More Info

Unexplained weight loss can be a concerning symptom, especially when it occurs alongside other symptoms such as palpitations, tremors, and gastrointestinal issues. In your case, despite having normal thyroid function tests (T3, TSH, and Free T4), it is essential to explore other potential causes for your weight loss and associated symptoms.

Firstly, it is important to understand that weight loss can be attributed to a variety of factors beyond thyroid dysfunction. While hyperthyroidism (overactive thyroid) is a common cause of weight loss, your normal thyroid hormone levels suggest that this is not the underlying issue in your case. Here are some possible explanations for your symptoms and weight loss:
1. Psychological Factors: Anxiety and stress can significantly impact your appetite and eating habits, leading to weight loss. You mentioned feeling extremely tense, which could contribute to gastrointestinal symptoms like chronic diarrhea and a lack of appetite. Conditions such as generalized anxiety disorder or panic disorder can manifest with physical symptoms, including palpitations and gastrointestinal disturbances.

2. Gastrointestinal Disorders: Chronic diarrhea and changes in bowel habits can lead to weight loss due to malabsorption or inadequate nutrient intake. Conditions such as irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), or infections could be contributing factors. A consultation with a gastroenterologist may be warranted to investigate these possibilities further.

3. Cardiac Issues: Given your history of mitral valve prolapse, it is essential to consider whether your heart condition could be contributing to your symptoms. Palpitations and rapid heart rate can be associated with anxiety, but they can also indicate underlying cardiac issues that may need further evaluation.

4. Malignancies: While your doctor mentioned that cancer is less likely at your age, it is still a consideration, especially if there are other concerning symptoms or risk factors. Unexplained weight loss is often a red flag that warrants further investigation, including imaging studies or referrals to specialists.

5. Endocrine Disorders: Other endocrine disorders, such as adrenal insufficiency or diabetes, could also lead to weight loss. These conditions can affect metabolism and appetite, leading to unintended weight changes.

6. Nutritional Deficiencies: A lack of essential nutrients due to poor dietary intake or malabsorption can lead to weight loss and other symptoms. A thorough dietary assessment may help identify any deficiencies that need to be addressed.

In conclusion, while your thyroid levels are normal, it is crucial to consider a comprehensive evaluation of your symptoms. A multidisciplinary approach involving a primary care physician, a gastroenterologist, and possibly a mental health professional could be beneficial. They can help rule out serious conditions and provide appropriate management for anxiety or gastrointestinal issues. It is essential to address both the physical and psychological aspects of your health to achieve a holistic understanding of your weight loss and overall well-being.

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