Differential Diagnosis

The patient's presentation of a hoarse voice, weight loss, unilateral swelling of the thyroid gland, and right recurrent laryngeal nerve palsy, in the context of Hashimoto's thyroiditis treated with thyroxine, suggests several potential diagnoses. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Medullary thyroid carcinoma: This diagnosis is highly plausible due to the patient's symptoms, including unilateral thyroid swelling and recurrent laryngeal nerve palsy, which can be indicative of a thyroid malignancy. Medullary thyroid carcinoma can present with these symptoms and is known to cause nerve palsies due to local invasion.

• Other Likely Diagnoses

  • Anaplastic thyroid carcinoma: Although less common, anaplastic thyroid carcinoma is aggressive and can cause rapid growth, leading to symptoms like those presented by the patient, including nerve palsies and significant weight loss. Its aggressive nature makes it a consideration in this scenario.
  • Single thyroid nodule: A single thyroid nodule, especially if it's a malignancy like papillary or follicular thyroid cancer, could explain the unilateral swelling and potentially the nerve palsy if the nodule is large enough or has invaded nearby structures.

• Do Not Miss Diagnoses

  • Thyroid lymphoma: This is a rare condition but can present with rapid thyroid enlargement and symptoms similar to those described. It's crucial not to miss this diagnosis due to its potential for aggressive behavior and the need for prompt treatment.
  • Metastasis to the thyroid: Although rare, metastases to the thyroid gland from other primary cancers can occur and might present with similar symptoms, including weight loss and nerve involvement.

• Rare Diagnoses

  • Thyroglossal cyst: While thyroglossal duct cysts can present as neck masses, they are less likely to cause recurrent laryngeal nerve palsy or significant weight loss. This diagnosis seems less probable given the patient's full clinical picture.
  • Other rare thyroid malignancies: Such as thyroid sarcomas or other uncommon thyroid cancers, which could potentially explain the patient's symptoms but are much less common than the other listed diagnoses.