Differential Diagnosis
- Single most likely diagnosis
- Hyperthyroidism (specifically, T3-toxicosis): This condition is characterized by high levels of T3, which can cause symptoms such as atrial fibrillation (Afib), muscle pain, and weight loss. The low TSH level supports this diagnosis, as it indicates that the thyroid gland is overactive. The normal thyroid ultrasound does not rule out this diagnosis, as some cases of hyperthyroidism may not have visible abnormalities on ultrasound.
- Other Likely diagnoses
- Thyrotoxicosis factitia: This condition occurs when a person takes excessive amounts of thyroid hormone, leading to symptoms of hyperthyroidism. The high T3 level and low TSH level could be consistent with this diagnosis.
- Subclinical hyperthyroidism: This condition is characterized by a low TSH level with normal T3 and T4 levels. However, some patients may have mildly elevated T3 levels, which could contribute to symptoms such as Afib and muscle pain.
- Cardiac causes of Afib (e.g., cardiomyopathy, valvular disease): While the thyroid abnormalities may be contributing to the Afib, it is possible that there is an underlying cardiac condition that is also playing a role.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Thyroid storm: This is a life-threatening condition that occurs when the body is exposed to extremely high levels of thyroid hormone. Symptoms can include Afib, muscle pain, and other systemic symptoms. Although the patient's T3 level is not extremely high, thyroid storm is a diagnosis that should not be missed.
- Cardiac tamponade or other cardiac emergencies: The repeated episodes of Afib could be a sign of an underlying cardiac condition that requires urgent attention.
- Pulmonary embolism: This is a rare but potentially life-threatening condition that could cause Afib and other symptoms.
- Rare diagnoses
- T3-secreting thyroid nodule: This is a rare condition in which a thyroid nodule produces excess T3, leading to symptoms of hyperthyroidism.
- Struma ovarii: This is a rare ovarian tumor that can produce thyroid hormone, leading to symptoms of hyperthyroidism.
- Autoimmune causes of hyperthyroidism (e.g., Graves' disease): While these conditions are not typically associated with a normal thyroid ultrasound, they are possible causes of hyperthyroidism and should be considered in the differential diagnosis.