Thyrotoxicosis associated with a molar pregnancy and hyperemesis gravidarum.
Ghaffar AH, Shaikh H, Meeran K, Hatfield E. Imperial Centre for Endocrinology, Charing Cross Hospital, Fulham Palace Road, London.
A twenty-six year old woman presented to hospital with two to three weeks of nausea, vomiting, anxiety, palpitations and weight loss. A recent home pregnancy test had been positive, and this was a planned conception. She was rehydrated and given anti-emetics.
An in-patient ultrasound demonstrated a vascular mass within the uterus distorting the endometrial cavity. This was consistent with a molar pregnancy. Given the findings and her presentation further bloods were sent. These showed a β-hCG of over 27 000 IU/L, a suppressed TSH and a T4 of 73.4 pmol/L (NR 9-25). She underwent a dilatation and curettage and was commenced on intramuscular methotrexate. She was also commenced on carbimazole, and a small dose of propranolol, and was managed as an out-patient. After a week of starting carbimazole her TSH remained suppressed, but her T4 had fallen to 15.5 pmol/L and T3 was 4.2 pmol/L (NR 3-5.8). After 3 weeks of taking carbimazole 20mg per day the TSH was 0.09 mU/L, T4 12.6 pmol/L and T3 4.4 pmol/L. The carbimazole was reduced to 10mg per day. The β-hCG had fallen to 20 281 mU/L. Two weeks later her TSH was 1.3 pmol/L, T4 11.7 pmol/L and the β-hCG had fallen dramatically to 99 mU/L. The carbimazole was reduced to 5 mg, and stopped shortly thereafter and she remained biochemically euthyroid. β-hCG levels also subsequently normalised. She has remained well.
Hyperemesis is common in the early stages of pregnancy, and is related to the production of hCG. hCG is a glycoprotein and a heterodimer consisting of α and β subunits. The α subunit is identical to that found in FSH, LH and TSH. As a result of the similarity with TSH, high hCG levels bind to the TSH receptor and this stimulates the thyroid. This is counter-balanced in pregnancy by a fall in TSH levels to maintain euthyroidism. If hCG levels are very high, as occurs in a molar pregnancy then overt clinical and biochemical thyrotoxicosis can occur. This then requires treatment with thionamides until such time that the molar pregnancy is treated and hCG levels fall. Endocrinologists, obstetricians and oncologists need to be aware of the effect of hCG on the thyroid and need to work together to care for patients like the one described.