Differential Diagnosis for a Painless Thyroid Lump

The patient presents with a visible, painless lump in her neck, an enlarged, nontender thyroid gland, and abnormal thyroid function studies (elevated TSH and normal T4 levels). Based on these findings, the differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis

  • Hashimoto Thyroiditis: This is the most likely diagnosis given the patient's presentation. Hashimoto thyroiditis is an autoimmune condition that leads to hypothyroidism, often presenting with a goiter (enlarged thyroid gland) and elevated TSH levels. The condition is common in women and can cause the thyroid gland to become enlarged and firm, though it may be nontender. The normal T4 level with an elevated TSH suggests a subclinical hypothyroidism, which is consistent with early stages of Hashimoto thyroiditis.

• Other Likely Diagnoses

  • Multinodular Goiter: This condition involves the enlargement of the thyroid gland with multiple nodules, which can be functional or non-functional. While it might not directly explain the elevated TSH, some nodules could be producing thyroid hormones, leading to a compensatory increase in TSH. However, the lack of tenderness and the specific laboratory findings make this less likely than Hashimoto thyroiditis.
  • Thyroid Adenoma: A single nodule in the thyroid gland could be an adenoma, which is usually benign. However, the presence of an enlarged, nontender thyroid gland and the laboratory findings suggest a more diffuse process like Hashimoto thyroiditis rather than a focal lesion like an adenoma.

• Do Not Miss Diagnoses

  • Thyroid Lymphoma: Although rare, thyroid lymphoma can present with a rapidly enlarging neck mass and can be associated with hypothyroidism. It is crucial to consider this diagnosis due to its potential for aggressive behavior and the need for prompt treatment.
  • Papillary Thyroid Carcinoma: This is the most common type of thyroid cancer and can present as a painless thyroid nodule or goiter. While the patient's age and sex are consistent with this diagnosis, the lack of other symptoms (e.g., hoarseness, difficulty swallowing) and the specific laboratory findings make it less likely. However, given the potential severity of thyroid cancer, it should not be missed.

• Rare Diagnoses

  • Riedel's Thyroiditis: A rare form of chronic thyroiditis characterized by a hard, fibrotic thyroid gland that can cause compressive symptoms. It is less likely given the patient's lack of symptoms such as difficulty swallowing or breathing.
  • De Quervain's Thyroiditis: A rare inflammatory condition of the thyroid gland, usually triggered by a viral infection, leading to neck pain and transient hyperthyroidism followed by hypothyroidism. The patient's painless presentation and stable laboratory findings make this diagnosis less likely.