Thyroid Nodule Approach - USMLE Step 3 Review - Endocrinology Topic 1

Approach to Thyroid Nodules

Many students have questions about how to approach a Thyroid Nodule. The questions on thyroid nodule are often very highyield on Endocrinology portion of USMLE Step 3. Our experience showed that most students usually got them wrong and have wrongly interpreted the guidelines. Many books give different recommendations and students find it confusing. So, we made an attempt to briefly summarize the guidelines here. These recommendations are taken from most popular updated sources in medicine and american college of endocrinology guidelines.

A. Approach – Palpable Thyroid Nodule
Cold nodules are more likely to be malignant when compared to hot nodules ( hot/ functioning nodule virtually rules out malignancy)

1. If thyroid nodule palpable --> Get TSH First.
a) If High TSH – suggests cold nodule/ Hashimatos --> Get FNAC (source: NEJM)( AACE recommends ultrasound as the next step here because hashimatos may have benign nodularity that regress with therapy and ultrasound will help to see if there are suspicious features. If U/S suspicious, then FNAC is recommended. This may be optimal approach because hurthle cells of hashimatos may cause false positives on cytology if the FNAC is obtained from such benign nodule --> so, we would recommend that you choose ultrasound as your next step if that is there in your MCQ choices. If the choices have no ultrasound, choose FNAC as answer). Further approach will depend on FNAC results. For hypothyroidism issue - Treat with levothyroxine if overt hypothyroidism or if subclinical hypothyroidism that warrants treatment.
b) If TSH normal – suggests cold nodule - next step, get FNAC.
c) If TSH low - suggests Hot nodule ( toxic adenoma) but not confirmative (What if there is GRAVES in the surrounding tissue and this is a cold nodule?) - so, next step get RAIU scan. If RAIU scan shows Hot nodule treat with I131 ( if there is overt hyperthyroidism from this toxic adenoma) or just observation. Cold nodules are more likely to be malignant when compared to hot nodules ( hot/ functioning nodule virtually rules out malignancy). If RAIU shows COLD nodule, get FNAC.

Further Approach depends on FNAC results :
a) If FNAC is benign - Suppressive therapy with LT4 in some cases if cosmetically warranted
b) If FNAC is malignant/ suspicious - SURGERY
c) If FNAC is non-diagnostic - repeat FNAC. If repeat FNAC is again non-diagnosotic, surgery

B) Approach - Thyroid Incidentalomas

Thyroid Incidentalomas – These are those nodules ( not the palpable ones) detected on ultrasound such as when ultrasound was done for other purposes such as for other palpable thyroid abnormalities or during carotid artery imaging or ultrasound done for hyperparathyroidism).

The next step in such nodules discovered on the ultrasound depends upon the features of the nodule.
FNAC is indicated in such incidentally discovered thyroid nodules if :
- Nodule > 10 mm in diameter
- On ultrasound, if nodule has suspicious features of malignancy à hypoechoic, microcalcifications, irregular shape, blurred margin or increased vascularity
- If there are risk factors for thyroid cancer ( family history, childhood neck irradiation)

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