What is the best initial investigation for a patient with hypothyroidism (Underactive Thyroid) presenting with a thyroid lump, hoarseness of voice, dysphagia (Difficulty Swallowing), and a woody firm fixed thyroid swelling?

Best Investigation for Thyroid Lump with Concerning Features

Fine needle aspiration cytology (FNAC) is the best initial investigation for a patient with hypothyroidism presenting with a thyroid lump, hoarseness of voice, dysphagia, and a woody firm fixed thyroid swelling. 1

Clinical Presentation Analysis

The patient presents with several concerning features:

• Woody firm fixed thyroid swelling
• Hoarseness of voice
• Dysphagia
• Pre-existing hypothyroidism

These clinical features significantly increase the likelihood of malignancy:

• The presence of a firm, fixed nodule increases the probability of malignancy approximately 7-fold 1
• Hoarseness (suggesting vocal cord involvement) and dysphagia (difficulty swallowing) indicate possible invasion of surrounding structures
• The woody texture suggests infiltrative disease

Diagnostic Approach

Why FNAC is the Best Choice:

1. Direct tissue sampling: FNAC provides cellular material for cytological examination, allowing direct assessment of malignancy
2. High diagnostic accuracy: Studies show FNAC has sensitivity of 84-90% and specificity of 53-99% for detecting thyroid malignancy 2, 3
3. Guideline recommendation: In patients who are clinically euthyroid (or with known hypothyroidism), FNAC of the nodule is recommended as the first diagnostic test before any imaging studies 1
4. Minimally invasive: FNAC is less invasive than open biopsy with fewer complications

Why Other Options Are Less Appropriate:

B. Open biopsy:

• Unnecessarily invasive as a first-line investigation
• Associated with higher complication rates
• Should be reserved for when FNAC is non-diagnostic or inconclusive

C. TSH:

• The patient already has a known case of hypothyroidism
• TSH levels would not help determine the nature of the thyroid lump
• While TSH should be known before FNAC, it's not the primary diagnostic test for a suspicious nodule 1

D. Iodine isotope scan:

• Low positive predictive value for malignancy
• Most nodules appear as "cold" on scan, but most cold nodules are benign 1
• In euthyroid patients, radioisotope scanning is not helpful in determining malignancy 1

Diagnostic Algorithm

1. Initial evaluation: Assess clinical features (firmness, fixation, voice changes, dysphagia)
2. First-line investigation: FNAC of the thyroid nodule
3. Supportive imaging: Ultrasound of thyroid and central neck (ideally performed before or during FNAC for guidance)
4. Follow-up based on FNAC results:
   • Malignant/suspicious: Surgical planning
   • Indeterminate: Consider repeat FNAC or molecular testing
   • Benign: Observation with follow-up ultrasound

Important Considerations

• Ultrasound guidance improves the accuracy of FNAC and should be used when available
• The cytology should be interpreted by a pathologist with expertise in thyroid disorders
• Even with a negative FNAC, the presence of concerning clinical features (as in this case) should prompt further investigation
• The combination of multiple suspicious clinical features (firm, fixed nodule, hoarseness, dysphagia) makes the likelihood of thyroid cancer very high 1

FNAC remains the cornerstone of initial evaluation for suspicious thyroid nodules, providing the most direct and reliable information to guide management decisions.