Different aetiologies in post-partum thyroiditis?

During a 4 year period 19 women with post-partum onset of thyroid dysfunction have been seen in our clinic. Five women had high radioiodine uptake thyrotoxicosis (Graves' disease). Twelve women had hypothyroid symptoms starting within 3-6 months of delivery. All of these women had thyroid microsomal and/or cytoplasmic autoantibodies and thyroid lymphocytic infiltration suggesting aggravation of pre-existing subclinical autoimmune thyroiditis (Hashimoto's disease). At follow-up thyroid function gradually improved in all but signs of persistent thyroid hypofunction remained in seven. Thus women developing symptomatic postpartum hypothyroidism should be followed regularly and when thyroxine treatment is commenced in the post-partum period, it has to be continued indefinitely in many cases. Two women presented with transient low radioiodine uptake thyrotoxicosis and a small painless goitre. Thyroid cytology revealed thyroiditis but they had no thyroid autoantibodies. When followed after a succeeding delivery none of these women developed post-partum thyroid dysfunction in contrast to women in the autoimmune group. Probably the aetiology of thyroid dysfunction in these 2 women was different.