The long-term effect of replacement therapy in a short girl with autoimmune atrophic thyroiditis of prepubertal onset.

A 9 yr 11 mo old girl was admitted to our hospital because of short stature. Her growth rate gradually decreased and her height was 120 cm (-2.5 SD) on admission. The mother's and father's heights were 157 cm (-0.2 SD) and 163 cm (-1.3 SD), respectively. Her bone age was retarded (6 yr 10 mo). An MRI indicated pituitary enlargement, which mimicked adenoma. Evaluation of the pituitary-thyroid axis and thyroid function proved she had primary hypothyroidism (T3 0.5 ng/ml, T4 1.0 μg/dl, TSH 1,030 μU/ml). These findings, thyroid autoantibody (anti-microsome antibody 400 xs) and histopathology (moderate fibrosis and mild lymphocytic infiltration) suggested acquired hypothyroidism due to autoimmune atrophic thyroiditis of prepubertal onset. Since the evaluation, she has been treated with levothyroxine. The pituitary enlargement disappeared within 3 mo after levothyroxine replacement. The growth rate increased and her height reached 153.2 cm (-1.0 SD) during 10 yr replacement (at 19 yr 11 mo of age). An improvement in her final height was obtained by long-term thyroid hormone replacement therapy. Enough endocrinological study and repeated MRI evaluation are necessary in cases of pituitary enlargement which mimics adenoma before considering surgery.