Dr. Hale's comments about I-131 were greatly appreciated.  On reviewing
the basis for my previous comments, the AAP Statement in Pediatrics Jan.
1994, I noted that their figure of 2-14 days of presence of radioactivity
in milk was based on studies which were old (1950's and '60's), and
although I have not reviewed them, the titles suggest use of I-131 in
diagnostic studies, presumably using a much lower dose than that required
for ablation of the thyroid gland.  My apologies for quoting these
figures without reviewing their sources.  I still don't see any evidence
that the issue of potential breast cancer in the lactating breast after
I-131 exposure has been studied, but this may be a moot point if the
length of time for breastfeeding cessation is so long that a return to
breastfeeding is unlikely.  Since there are two other alternatives as
treatment for Graves' disease, i.e. medical therapy with PTU (compatible
with breastfeeding) or surgical excision of the thyroid, I would think
that those two options would be preferable to a mother who wishes to
continue breastfeeding.
While on the subject of Graves' disease, I currently have a patient at 32
weeks gestation who has had Graves' for years and has been suppressed
with PTU.  The plan is to continue PTU while breastfeeding.  Her
endocrinologist recently did a thyroid stimulating immunoglobulin test on
her, which was high and suggests a significant risk of neonatal
thyrotoxicosis in her baby.  I looked up what if any relevance this may
have on her breastfeeding, and the only reference that addressed this was
Ruth Lawrence in Medical Clinics of North America sometime in 1989 (the
reference is not handy, but I can get it for anyone who requests it).
She suggested that little of this immunoglobulin gets absorbed in baby's GI
tract, and that no increased risk of neonatal thyrotoxicosis was found.
Does anyone know of any other references about this?  Thanks, Alicia.
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