Source: Carcinogenesis  |  Posted 9 years ago

By Paula Moyer

Special to DG News

SAN FRANCISCO, CA -- June 24, 2002 -- The conventional practice of administering triiodothyronine (T3) therapy after thyroidectomy or thyroxine (T4) withdrawal in patients with differentiated thyroid cancer may be unnecessary.

These findings were presented here June 23rd at ENDO 2002, the 84th annual meeting of the Endocrine society.

The investigators noted that, whether T3 is used or not, patients develop elevated levels of thyroid-stimulating hormone (TSH) within two weeks after either thyroidectomy or T4 withdrawal.

Conventional management of patients who have undergone total thyroidectomy for differentiated thyroid cancer consists of radioactive iodine (I131), used for either diagnostic or therapeutic purposes. In preparation for I131 administration, most endocrinologists treat patients with T3 alone or after initial therapy with T4. They then withdraw T3 and administer I131 after levels of serum thyroid-stimulating hormone (TSH) reach >30 mU/L.

The investigators hypothesised that serum TSH levels would increase rapidly after thyroidectomy and also after cessation of T4 therapy without the use of T3. Therefore, they reasoned, physicians could identify patients with elevated levels by frequent measurements of serum TSH, before they developed hypothyroidism symptoms.

To determine how rapidly serum TSH levels would increase after either thyroidectomy or T4 withdrawal, they observed 45 patients immediately after thyroidectomy and 43 patients who had been on suppressive therapy for more than one year, in whom T4 was withdrawn.

Serum TSH levels were measured three times weekly, starting six to 10 days after thyroidectomy or T4 withdrawal, as well as serum free T4 and Tg levels, and patients were assessed for clinical signs and symptoms of hypothyroidism before I131 administration.

The means serum TSH levels for the thyroidectomy patients were 37.4 +/- 19.9 mU/L nine to 11 days after surgery, 49.3 +/- 22.0 mU/L on postoperative days 12-14, 57.7 +/- 31.4 on days 15-17, 75.4 +/- 50.2 mU/L on days 18-20, 77.5 +/- 41.8 mU/L on days 21-23, and 85.9 +/- 46.2 mU/L on days 24-26.

For patients undergoing T4 withdrawal, the mean serum TSH levels were 15.5 +/- 11.6 mU/L on days 9-11, 29.8 +/- 22.5 mU/L on days 12-14, 47.9 +/- 47.9 mU/L on days 15-17, 46.3 +/- 27.7 mU/L on days 18-20, and 74.2 +/- 55.2 mU/L on days 21-23.

The difference in mean serum TSH levels between the thyroidectomy patients and those who underwent T4 withdrawal was statistically significant through day 14 (p=0.0011 for days 9-11, p=0.003 for days 12-14). However, from day 15 on, significant difference between the groups? TSH levels diminished (p=0.472 for days 15-17, p=0.136 for days 18-20, and p=0.859 for days 21-23).

After thyroidectomy, the investigators observed that serum TSH levels increase as early as day 6 and were >30 mU/L after seven to 36 days (15.1?6.0 days). Similarly, serum TSH levels increased after T4 withdrawal reaching >30 mU/L in 9 to 34 days (18.5?5.3 days). They found that patients in both groups had minimal symptoms of hypothyroidism despite low serum free T4 levels. Serum Tg levels varied within the two groups.

The investigators concluded that in most patients, serum TSH levels achieve concentrations greater than 30 mU/L two weeks after total thyroidectomy or T4 withdrawal, respectively.

"Our findings cast doubt on the necessity and benefit of using T3 for these patients," said lead investigator Dina I Serhal, MD, endocrine fellow at Case Western Reserve University in Cleveland, Ohio. "Instead, we recommend that physicians obtain patients' serum TSH levels two to three times weekly starting 10 days after thyroidectomy or T4 withdrawal, in order to identify and therefore minimise symptoms of hypothyroidism."

Her collaborator for this study was Baha M. Arafah, MD, program director for the thyroid service at Case Western Reserve University.