What is the best investigation for a patient with hypothyroidism presenting with a thyroid lump, hoarseness of voice, dysphagia, and a woody firm fixed thyroid swelling?

Fine Needle Aspiration Cytology (FNAC) is the Best Investigation for a Patient with Hypothyroidism Presenting with a Thyroid Lump

FNAC is the best initial investigation for a patient with hypothyroidism presenting with a thyroid lump, hoarseness of voice, dysphagia, and woody firm fixed thyroid swelling, as these clinical features strongly suggest anaplastic thyroid carcinoma requiring immediate tissue diagnosis. 1

Clinical Presentation Analysis

• The presentation of a woody firm fixed thyroid swelling with hoarseness of voice and dysphagia in a patient with hypothyroidism is highly concerning for anaplastic thyroid carcinoma (ATC), which requires urgent tissue diagnosis 1
• Hoarseness indicates potential recurrent laryngeal nerve involvement, which is common in invasive thyroid malignancies 1
• Dysphagia suggests esophageal compression or invasion, another concerning feature for malignancy 1
• The "woody firm fixed" nature of the thyroid swelling is a classic description of anaplastic thyroid carcinoma, which has a disease-specific mortality approaching 100% 1

Diagnostic Algorithm

Step 1: Initial Tissue Diagnosis

• FNAC is the preferred first-line diagnostic test for suspicious thyroid nodules before any imaging studies are performed 1
• FNAC provides rapid cytologic examination to categorize the mass as carcinoma (papillary, medullary, or anaplastic), follicular neoplasm, or other pathology 1
• The woody firm fixed nature of the nodule with associated symptoms significantly increases the pretest probability of malignancy, making tissue diagnosis the priority 1

Step 2: Additional Imaging (After FNAC)

• If FNAC confirms or suggests malignancy, then cross-sectional imaging (CT or MRI) should be performed to assess extent of disease 1
• Ultrasound alone is insufficient when invasive features are present clinically 1

Why Other Options Are Inferior

• Open biopsy (Option B): More invasive than necessary as first-line investigation; FNAC should be attempted first as it is less invasive and provides adequate diagnostic information in most cases 1
• TSH (Option C): The patient already has a known diagnosis of hypothyroidism, and TSH levels will not provide diagnostic information about the nature of the thyroid mass with concerning features 2
• Iodine isotope (Option D): Not helpful in this scenario as anaplastic carcinomas typically do not concentrate iodine, making radioactive iodine imaging ineffective for diagnosis 1

Important Clinical Considerations

• If FNAC results are suspicious or not definitive, core or surgical biopsy should then be performed to establish the diagnosis 1
• Discriminating between ATC and other primary thyroid malignancies (medullary thyroid carcinoma, thyroid lymphoma) can sometimes be difficult with FNAC alone 1
• Pathology slides should be reviewed at the treating institution by a pathologist with expertise in thyroid disorders 1
• The patient's history of hypothyroidism does not exclude the possibility of thyroid malignancy; in fact, approximately 50% of patients with anaplastic thyroid carcinoma have either prior or coexisting differentiated thyroid carcinoma 1

Potential Pitfalls

• Relying solely on imaging without tissue diagnosis can delay appropriate treatment 1
• False-negative FNAC results can occur; therefore, a reassuring FNA should not override worrisome clinical findings such as the woody firm fixed nature of the nodule 1
• Anaplastic thyroid carcinoma requires urgent management due to its aggressive nature and poor prognosis 1
• The appearance of ATCs varies widely with mixed morphologies, making expert cytopathology review essential 1