2017 – PAGE 70-71 – ENDOCRINOLOGY
THYROID DISORDERS—KEY TERMINOLOGY
DEFINITIONS of Thyroglobulin, Thyroxine-Binding Globulin, Thyroxine, and Free T4
- THYROGLOBULIN: This protein is found only in the thyroid It is used to make thyroid hormones.
- THYROXINE-BINDING GLOBULIN; TBG is responsible for carrying thyroid hormones in the blood.
- THYROXINE: THYROXINE = T4 = Hormone that is BOUND to TBG and in the blood and INACTIVE
- FREE T4: FREE T4 = FT4 = the ACTIVE hormone in the blood
Thyroxine-binding globulin deficiency is an X-linked disease in which the newborn screen (NBS) reveals normal TSH but LOW T4 values. NBS is measuring T4 (BOUND hormone), which is low because there is a TBG deficiency! Get a FREE T4 as the next step. It should be NORMAL. Another option is to get a TBG level, which should be low. NO treatment is indicated. So if TSH is normal but T4 is low on NBS → NO TREATMENT.
PEARL: TSH is the barometer for the thyroid. If it’s normal, there’s probably no clinical problem.
Hypothyroidism and congenital hypothyroidism are diagnosed with elevated TSH and a low Free T4 (get T4 if FT4 not offered on exam). If asked how to screen, choose TSH. In utero, some of mom’s thyroxine crosses the placenta so babies may by asymptomatic at birth. Signs of hypothyroidism may include puffiness, large tongue, hoarse cry, umbilical hernia, hypotonia, large anterior fontanelle (AF), open posterior fontanelle (PF), constipation, and mottling. Possible etiologies include:
- Dysgenesis is the most common reason.
- Abnormal thyroid development somewhere between the base of the tongue and the normal position. Mass would be midline but not cystic. Removal can result in worsening of hypothyroidism. Once a patient is started on Thyroxine, check T4 and TSH in 1 month.
- Acquired Hypothyroidismis more common than Congenital Hypothyroidism. If a patient is euthyroid up to age 5 years, the IQ should be fine. If the patient is short, it is OKAY to start the patient on meds that can help with catch-up growth.
- HASHIMOTO’S THYROIDITIS = CHRONIC LYMPHOCITIC THYROIDITIS: Hashimoto’s Thyroiditis, or chronic lymphocytic thyroiditis, results in HYPOTHYRO Labs include +anti-TPO or +anti-thyroglobulins, low T4 with an elevated TSH. The patient is likely to have a painless, firm GOITER/thyromegaly.
- “Infiltration/inflammation/destruction?” of the gland results in low thyroid hormone (so low T4), which results in an elevation in TSH. Sometimes, T4 or FT4 may be normal because of the extremely high TSH. A rare complication is transient thyrotoxicosis. Radioactive Iodine Uptake in HashimOtO’s is LOW. “The thyroid is being destroyed, so how could it take up any iodine?”
- PEARL: If TSH is abnormal on the NBS, start Levothyroxine now (and get labs). You can always ask questions later. Urgency is due to the tremendous cognitive delays that can occur if therapy is not started by 4 weeks. Continue medication until repeat labs are back.
A thyroglossal duct cyst is a midline lesion on anterior neck. As many as half of all thyroglossal duct cysts can get infected, which then increases the chances of recurrence. Therefore the treatment of choice is surgical excision IF the thyroid is intact. For the exam, if they describe a midline cystic lesion, choose this as the diagnosis. Diagnose by ultrasound and do a thyroid scan to ensure the thyroid gland is intact because sometimes the only functioning thyroid tissue may be within the cyst itself. If the thyroid gland is okay, remove the cyst!
PEARL: Don’t get confused with a RANULA, which is a painless, mucous and CYSTIC mass usually near the inner lips or under the tongue. This might be midline, will have clear contents and should be treated by removal.
Thyroid nodules are more likely to be malignant in kids than in adults, so a must be worked up. Get thyroid function tests (low TSH suggest possibility of a hyperfunctioning “hot” nodule) and an ultrasound to better assess size, location, and characteristics. If ultrasound is not a choice, get radioactive imaging, which will help distinguish between hot and cold nodules. Fine needle aspiration is then the usual method of choice to diagnose lesions that are still suspicious. COLD NODULE = INACTIVE TISSUE = BAD!
PEARL: Some of the symptoms of hyperthyroidism may be disguised as “hyperactivity, disorganized thinking, and trouble sleeping.”
PEARL: If a patient has a goiter, more information is needed to differentiate between hypothyroidism and hyperthyroidism.
MNEMONIC: PTU can be quite toxic so it is NOT a first-line agent. P-T-U = Potentially Toxic, UGH!
MNEMONIC: If you look at the letters for GravEs DisEasE versus HashimOtO’s ThyrOiditis, you’ll notice that Grave’s Disease has plenty of E’s in it, like hypErthyroidism, while Hashimoto’s doesn’t have a single E in it! Just the O’s, like hypOthyroidism.