Primary hypothyroidism in juvenile population often leads to retardation of linear growth and/or delayed puberty. However, rarely sexual precocity may occur in juvenile hypothyroidism. This syndrome of incomplete isosexual precocity and juvenile hypothyroidism is called Van Wyk-Grumbach syndrome. Bone age is delayed unlike other forms of sexual precocity where advanced bone age is a rule. These two features(growth retardation and delayed bone age) points to primary hypothyroidism as the cause for sexual precocity. Juvenile hypothyroidism is due to auto-immune thyroid disease and rarely due to congenital hypothyroidism. Low fee T4 and high TSH confirms the diagnosis. Prolactin and FSH can be elevated in this syndrome. Galactorrhoea occurs due to hyperprolactinemia and can be spontaneous or present on gentle manipulation. Pubarche is not a feature. Pituitary often enlarges due to hyperplasia of thyrotrophs, lactotrophs and gonadotrophs and mistaken for pituitary tumor(1). Ovaries show multicystic appearance due to stimulatory effect of TSH(called specificity spillover) and FSH.
The exact mechanism is poorly understood. The increase in prolactin is mediated by rise in TRH secondary to loss of feedback inhibition by low levels of thyroid hormones. TSH and FSH acts on the FSH receptors in the ovary resulting in multicystic appearance and increased production of estradiol. In boys, the FSH and TSH act on the FSH receptors in sertoli cells causing testicular enlargement. Since no testosterone is produced, secondary sexual characters do not develop in boys except testicular enlargement. All manifestations including pituitary enlargement and multicystic appearance improve with treatment of thyroxine except testicular enlargement in boys.
Figure 1: USG showing multicystic ovaries