Hyperthyroidism — Low TSH

DIFFERENTIAL DIAGNOSIS of Low TSH & High FT4

**  Graves’ Disease

• Exophthalmus / Pretibial Myxedema diagnostic but not sensitive
• Radioiodine Uptake = normal or high
• ↑ TSH-receptor AB  [sensitive]
• ↑ Thyroid Stimulating Immunoglobins  [specific]

 **  Multinodular Goiter

• Palpable on exam
• Ultrasound to R/O suspicious nodules
• Biopsy suspicious nodules (FNA or excisional)

 **  Thyroiditis (viral)

• Painful & Tender thyroid gland
• Tests for Graves’ [above] are negative

 **  Painless Thyroiditis (autoimmune)

• Non-Tender thyroid gland
• Tests for Graves’ [above] are negative

 **  Postpartum Thyroiditis (autoimmune)

• <12 months post-delivery
• Non-Tender thyroid gland
• Tests for Graves’ [above] are negative

 **  Drug-Induced

• Lithium, Amiodarone, Interferon, imatinib, old cough syrups w/ iodine

 **  Trophoblastic Disease of Pregnancy

• Pregnancy Test
• If + then R/O choriocarcinoma

 **  Iatrogenic Hyperthyroidism

• L-thyroxine Rx’d for “goiter”

 **  Surreptitious

• L-Thyroxine obtained to ↓ wt

 **  Thyroid Nodule (usually euthyroid)

• Ultrasound; FNA; ? excisional Bx

**  Central Hyperthyroidism (rare)

• TSH ↑ / nl. but ↑ FT4
• Obtain MRI of Pituitary