The iodide perchlorate discharge test in women with previous post‐partum thyroiditis: relationship to sonographic appearance and thyroid function

Summary BACKGROUND Post-partum thyroid disease occurs in 50% of anti-thyroid peroxidase (TPO) antibody positive women (detected at 16 weeks' gestation) and is characterized by a transient episode of hyper, hypo or hyper-hypo thyroidism. In approximately 20% of these women the hypothyroidism is permanent. However, the extent of long-term thyroid dysfunction, possibly mediated by immune attack, in those anti-TPO Ab + ve women who have had only transient or no thyroid dysfunction during the postpartum period is not clear. OBJECTIVE We have therefore studied the frequency of iodide organification defects by iodide perchlorate discharge testing, and of thyroid morphological abnormalities by ultrasound scanning in euthyroid women following their episode of post-partum thyroiditis (PPT). DESIGN The study group comprised 17 women with previous PPT (PPT +ve) and 12 women who had positive anti-TPO antibodies during pregnancy but who did not develop PPT (PPT-ve). Women were studied 15-47 months following their episode of PPT. RESULTS Iodide perchlorate discharge tests were positive (more than 10% discharge) in 7 (41 %) PPT + ve and 5 (42%) PPT-ve subjects (P = NS). Morphological abnormalities on thyroid ultrasound were detected in 7 of 14 (50%) PPT + ve and 7 of 9 (77%) PPT-ve subjects (P = NS). There was a strong association between abnormalities of iodide organification and morphology: of 11 subjects with positive iodide perchlorate discharge tests, 10 had abnormal (positive) ultrasound scans; of 12 subjects with negative iodide perchlorate discharge tests 8 had negative ultrasound scans (P= 0.013, Fisher's exact test). CONCLUSIONS Long-term subtle defects of thyroid function and morphology are common in women with anti-TPO antibodies in pregnancy, whether or not they develop postpartum thyroiditis. The clinical significance of these findings is unclear but a continuing thyroid pathological process is suggested.