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Special Feature
August 1998

Pathological Case of the Month

Author Affiliations



Copyright 1998 American Medical Association. All Rights Reserved. Applicable FARS/DFARS Restrictions Apply to Government Use.1998

Arch Pediatr Adolesc Med. 1998;152(8):828. doi:
Diagnosis and Discussion: Hyperthyroidism With a Hydatidiform Mole

Figure 1. Hydropic chorionic villi with cisternae formation (hematoxylin-eosin, original magnification ×4).

Figure 2. Trophoblastic proliferation (hematoxylin-eosin, original magnification ×20).

The mass was a hydatidiform mole (HM). Microscopic appearance was characterized by markedly swollen chorionic villi with apparently empty cisternae resulting from dissociation of loose villous connective tissue and diffuse trophoblastic hyperplasia. Recognizable vascular elements were rarely seen.

HMs occur in approximately 1 in 1000 pregnancies,1 but are rarely seen by pediatricians. The incidence of HMs in teenagers is 1.5- to 2-fold greater than in adult females.1 HMs are due to abnormal growth of the chorionic villi. An HM may be complete or partial. A complete HM has no fetal or normal placental tissue; a partial HM has fetal and/or placental tissue combined with the mole. Moles occur when a single 23,X sperm fertilizes an ovum without a nucleus, and then the chromosomes double. Thus, most moles have a karyotype of 46,XX and all the chromosomes are paternal in origin. The abnormal development seems due to the lack of maternal chromosomal contribution to the embryo.2

Patients with HMs typically present with vaginal bleeding but may have hyperemesis and other signs of early pregnancy. The β-hCG concentrations in blood usually exceed 200000 IU/L. Uterine size may be large for the stage of pregnancy. Whether complete or partial, HMs often create complications.

Hyperthyroidism is due to stimulation of the thyroid by hCG. The hCG is a glycoprotein hormone produced by trophoblastic tissue and composed of a unique β-subunit and an α-subunit that is similar to that of pituitary glycoprotein hormones, including TSH. Weak thyrotropic activity is seen with hCG≈0.04 to 0.5 µIU bovine TSH/IU hCG or 0.52±0.35 µIU human TSH/IU hCG.3,4 On a molar basis, hCG is 1/4000 as potent as human TSH in the TSH bioassay.5 Unlike normal pregnancies with β-hCG levels <100000 IU/L, in molar pregnancies values are often >200000. As the hCG level increases, its thyrotropic activity becomes more notable and the thyroid sufficiently stimulated to become hyperfunctioning. However, there is no direct correlation between the β-hCG and T4 or T3 levels (possibly because only a fragment of β-hCG and not the total β-hCG is measured on most assays). Therefore, the degree of elevation of the thyroid hormones cannot be predicted by the β-hCG level. The pituitary will decrease TSH production in response to the elevated T4 and T3 values, and the TSH level may be undetectable, as in Graves disease.

Teenagers have an increased risk of molar pregnancies. They will often deny or be unaware of their pregnancy and may present to their pediatrician reporting only vaginal bleeding or abdominal pain. When suspected, it is important to include laboratory assessment of thyroid function prior to surgery as signs and symptoms of hyperthyroidism may be subtle and masked by those due to the pregnancy. The complications that occur with HMs may also obscure the findings associated with hyperthyroidism. Even classic manifestations of thyrotoxicosis may be attributed to other complications if hyperthyroidism is not suspected. The thyroid itself usually appears normal, and the characteristic eye findings of Graves disease are absent.

Results of thyroid function tests often take 1 or 2 days to become available if not done emergently. Removal of the HM is usually scheduled soon after its diagnosis. Due to the undetected hyperthyroidism, the patient may become symptomatic with tachyarrhythmia, hyperthermia, and high-output cardiac failure and may even progress to potentially fatal thyroid storm during the surgical procedure.6 So, some patients may benefit from β-blockers and/or iodine administration prior to HM evacuation, both to control symptoms possibly present as well as to prevent other serious consequences, including thyroid storm. Propylthiouracil and methimazole usually take several days to become effective and are not appropriate for treatment in these cases.

Removing the HM, the source of hCG is gone and medication not needed. The β-hCG declines, as do the T4 and T3 levels; correspondingly TSH levels increase. Typically, the thyroid hormone levels return to normal in several weeks (perhaps 1 wk since the half-life of T4 is 7 days), as will those of β-hCG. If thyroid function does not return to normal within a month, another cause is likely.

Suspect a patient seen with an HM to be hyperthyroid to prevent complications both before and at surgery. If the patient appears clinically hyperthyroid, consider HM as most likely and evaluate and manage to suit.

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Article Information

Accepted for publication May 5, 1997.

Reprints: Juan C. Sanchez, MD, Mailman Center for Child Development, 1601 NW 12th Ave, Miami, Fla 33136.

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