Differential Diagnosis: Thyroid

Goiter: false positive

Not all patients you think have a large thyroid actually do.

Overestimation of the size of the thyroid can result from:

• A more easily palpable thyroid in a thin patient with less overriding tissue
• A higher placed thyroid (normal variant)
• A long, curving neck that enhances prominence and palpation of the gland (Modigliani drawing)
• Lesion behind thyroid, pressing it forward
• Enlargement of adjacent structure, mistaken for thyroid

Goiter: false negative

On some patients, you may miss detecting an enlarged thyroid.

Underestimation of the size of the thyroid can result from:

• Inadequate physical examination (most common cause)
• Short thick neck in patients, seen most commonly in the obese, elderly or pts with COPD.
• Atypical placement of thyroid ( retrosternal or lateral placement of lobes)

Etiology

Hypothyroidism

Primary thyroid gland failure due to chronic autoimmune thyroiditis (Hashimoto's thyroiditis) is the most common cause of hypothyroidism. Other frequent causes are previous radioactive idine therapy for hyperthyroidism and thyroid surgery. Subclinical hypothyroidism is most commonly due to autoimmune thyroiditis, or to inadequate replacement of hypothyroidism.

Hypothyroidism

The most common eitology of hyperthyroidism overall is Graves" Diseases, an immunologically mediated toxic goiter. The peak incidence is in patients in their 20's or 30's and is 5 times more likely in women than men. In the elderly, toxic nodular goiter (TNG) is more common than Graves' Disease. Other cuases of hyperthyroidisim include toxic adenoma, postpartum thyroiditis, subacute thyroiditis, and exogenous thyroid hormone ingestion.

Subacute thyroiditis is self-limited disease of viral origin that often follows an URI. Transient postpartum thyroiditis, also a self-limited disease, occurs in approximately 5% of women in the frst 3 to 6 months postpartum and increases the subsequent risk of developing primary thypothyroidism.

Thyroid Cancer

Thyroid cancer is rare (annual incidence of 0.004%) with low assoicated morbidity and mortality. In the US, there are 12,000 new cases of thyroid cancer and 1000 thyroid cancer related deaths annually. Almost all thyroid cancer (95%) presents as a thyroid nodule or neck mass.

Type of Thyroid Cancers (in order of decreasing frequency and increasing invasiveness)

• papillary (75%) - most common and least aggressive
• follicular (15%)
• medullary (5%)
• anaplastic (3%)

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