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Diagnosis of Postpartum Thyroid Disease
- Thyrotoxicosis and hypotyroidism 6 weeks to 6 months postpartum
- Usually +ve TPO Ab
- Low 123I thyroid uptake
- Hypoechogenicity on thyroid ultrasound
There are many changes that can occur in thyroid function after pregnancy
(Fig. 2). In women with a previous history of thyroid dysfunction, such
as Graves' disease or Hashimoto's disease an exacerbation of these conditions
may be seen. Postpartum thyroiditis is associated with an immune rebound
in women with preexisting thyroid antibodies. The reason for the dramatic
increase in antibody titre is not clear but is presumably related to a
removal of the socalled immunosuppression observed during normal pregnancy.
Thyrotoxicosis in the postpartum period may be due to a recurrence or the
development of new Graves' disease or to the thyrotoxic phase of postpartum
thyroiditis. Symptoms of thyrotoxicosis are much more evident in Graves'
disease. As postpartum thyrotoxicosis is a destructive process radioiodine
uptake will be very low at early and late times after isotope administration.
TSH receptor antibodies are not seen unless there is coexisting Graves'
disease. Thyrotoxicosis due to postpartum thyroiditis is diagnosed by a
suppressed TSH and thyroid isotope uptake together with an elevated FT4
or FT3, or elevated FT3 and FT4, with either set of criteria occurring
on more than one occasion. If possible a normal range of thyroid hormone
concentrations should be derived in the postpartum period as they fall
into a narrower range than the general population. Antibodies to thyroxine
and T3 may cause confusion in diagnosis but they are infrequent(20).
Figure 2:
Changes in thyroid hormones in various types of postpartum thyroid dysfunction. Numbers
indicate months postpartum. (After Amino N. et al4 with permission).
Hypothyroidism in the postpartum period occurs at
a median of 19 weeks but has been observed as late as 36 to 40 weeks after
birth. The symptoms are often dramatic and may develop before the decrease
in thyroid function is noted. The most frequent symptoms have been found
to be lack of energy, aches and pains, poor memory, dry skin and cold intolerance.
In the author's series hypothyroidism is defined as either TSH >3.6 mU/L
together with FT4 <8 pmol/l or FT3 <4.2 pmol/l or TSH 10mU/l on one
or more occasion. The use of thyroid ultrasonography has demonstrated diffuse
or multifocal echogenicity reflecting the abnormal thyroid morphology and
consistent with the known lymphocytic infiltration of the thyroid(21) (see
Fig. 3). The destructive nature of the thyroiditis is also shown by the
increase in urinary iodine excretion in the thyrotoxic as well as the hypothyroid
phase of the syndrome(22). In addition there is evidence that an early
rise in serum thyroglobulin (a further indicator of thyroid destruction)
may help in the identification of those women at risk of PPT(23).
Figure 3:
Longitudinal ultrasound scan of right lobe antibody positive patient 12 weeks postpartum. Note
multifocal hypoechoic areas (arrows).
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