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 fatigue, low energy, brittle nails, and arrhythmias like atrial fibrillation (Afib). 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 condition, as hyperthyroidism can be caused by conditions that do not affect the thyroid gland's structure, such as Graves' disease or a thyroid-stimulating hormone (TSH) receptor mutation.
- 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, especially if the patient has access to thyroid hormone medication. + Subclinical hyperthyroidism: This condition is characterized by a low TSH level with normal T3 and T4 levels. However, some patients may have a high T3 level, which could explain the patient's symptoms. The normal thyroid ultrasound does not rule out this condition. + Anxiety or stress-related condition: The patient's symptoms of fatigue, low energy, and brittle nails could be related to anxiety or stress, which can also cause Afib episodes.
- 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 thyroid gland is overactive, leading to severe symptoms such as high fever, tachycardia, and arrhythmias. Although the patient's symptoms are not severe enough to suggest a thyroid storm, it is essential to consider this condition due to its high mortality rate. + Cardiac conditions (e.g., cardiomyopathy, coronary artery disease): The patient's multiple Afib episodes could be related to an underlying cardiac condition, which would require prompt evaluation and treatment.
- Rare diagnoses + T3-secreting thyroid adenoma: This is a rare condition where a thyroid adenoma produces excess T3, leading to symptoms of hyperthyroidism. The normal thyroid ultrasound does not rule out this condition, as small adenomas may not be visible. + Resistance to thyroid hormone: This is a rare genetic condition where the body is resistant to the effects of thyroid hormone, leading to high levels of T3 and T4. The patient's symptoms could be consistent with this diagnosis, although it is rare. + Struma ovarii: This is a rare condition where thyroid tissue is present in the ovaries, leading to hyperthyroidism. The patient's symptoms could be consistent with this diagnosis, although it is rare and would require further evaluation.