Differential Diagnosis for a 35-year-old Female with Multinodular Thyroid Swelling

Single Most Likely Diagnosis

• Multinodular Goiter (MNG) with Subclinical Hyperthyroidism: This diagnosis is most likely due to the presence of a palpable multinodular thyroid swelling that moves with deglutition, low TSH levels despite normal T3 and T4, and ultrasound findings of a multinodular thyroid goiter. The compression of the trachea posteriorly by the swelling and the presence of reactive lymph nodes also support this diagnosis.

Other Likely Diagnoses

• Toxic Multinodular Goiter (TMNG): Although the patient's T3 and T4 levels are normal, the low TSH suggests some degree of thyroid hyperfunction, which could be due to a toxic multinodular goiter, especially if some nodules are autonomously functioning.
• Thyroiditis (e.g., Subacute or Chronic): The presence of reactive lymph nodes and a multinodular goiter could also suggest a form of thyroiditis, although the normal T3 and T4 levels and low TSH might not fully align with typical presentations of thyroiditis.
• Follicular or Papillary Thyroid Cancer: The presence of a multinodular goiter and reactive lymph nodes raises the concern for malignancy, particularly given the TI-RADS 2 score, which indicates a higher suspicion for cancer.

Do Not Miss Diagnoses

• Medullary Thyroid Carcinoma: This rare cancer can present with a thyroid mass and lymphadenopathy. It is crucial to consider due to its potential for aggressive behavior and the importance of early detection.
• Anaplastic Thyroid Cancer: Although rare, anaplastic thyroid cancer is highly aggressive and can present with a rapidly enlarging neck mass, which might initially be mistaken for a benign goiter.
• Lymphoma Involving the Thyroid: Primary thyroid lymphoma is rare but can present with a rapidly enlarging thyroid mass and lymphadenopathy, mimicking other thyroid pathologies.

Rare Diagnoses

• Thyroid Metastases from Other Cancers: Metastases to the thyroid from other primary cancers (e.g., breast, lung, kidney) are rare but should be considered, especially in patients with a known history of cancer.
• Riedel's Thyroiditis: A rare form of chronic thyroiditis characterized by a hard, fibrotic thyroid gland that can cause compressive symptoms, which might be considered given the tracheal compression noted in the patient.
• Thyroid Sarcoma: Extremely rare, thyroid sarcomas can present similarly to other thyroid masses but are distinguished by their malignant sarcomatous components.

Each of these diagnoses requires careful consideration of the patient's clinical presentation, laboratory findings, and imaging results to guide further investigation and treatment.