Differential Diagnosis
The patient's symptoms and laboratory results suggest a thyroid disorder. Here's a breakdown of the differential diagnosis:
Single most likely diagnosis
- D. Chronic lymphocytic thyroiditis: This is the most likely diagnosis due to the patient's symptoms of fatigue, cold intolerance, weight gain, and constipation, which are consistent with hypothyroidism. The laboratory results show a high TSH level, low free thyroxine level, and positive anti-TPO antibodies, which are characteristic of chronic lymphocytic thyroiditis (also known as Hashimoto's thyroiditis). The patient's history of a hyperthyroid phase (3 months of high energy, weight loss, and palpitations) followed by a hypothyroid phase is also consistent with this diagnosis.
Other Likely diagnoses
- B. Iodine deficiency: Although less likely, iodine deficiency can cause hypothyroidism, and the patient's symptoms could be consistent with this diagnosis. However, the presence of positive anti-TPO antibodies makes chronic lymphocytic thyroiditis more likely.
- E. Giant-cell thyroiditis: This condition can cause hypothyroidism, but it is typically associated with a painful thyroid gland, which is not present in this patient.
Do Not Miss
- A. Graves’ disease: Although the patient's current symptoms suggest hypothyroidism, her history of a hyperthyroid phase could be consistent with Graves' disease. However, the presence of positive anti-TPO antibodies and the lack of other symptoms such as exophthalmos or a bruit make this diagnosis less likely.
- C. Euthyroid sick syndrome: This condition can cause abnormal thyroid function tests in the setting of systemic illness, but the patient's symptoms and laboratory results are more consistent with a primary thyroid disorder.
Rare diagnoses
- Other rare causes of hypothyroidism, such as pituitary or hypothalamic disorders, or other forms of thyroiditis (e.g., radiation-induced or postpartum thyroiditis), are less likely given the patient's presentation and laboratory results.