Analysis of the factors affecting auxological response to GnRH agonist treatment and final height outcome in girls with idiopathic central precocious puberty.

The aim of this retrospective study was to analyze the factors which affected the auxological response to GnRH agonist treatment and the final height (FH) outcome in 71 girls with idiopathic and truly precocious (onset before 8 years) central puberty (CTPP) who had been treated with the same therapy protocol (Decapeptyl Depot, 60 microg/kg i.m. every 28 days) for at least 2 years (since 7.0+/-1. 3 (S.D.) years of age) and followed until puberty was completed and FH was reached. During the entire treatment period we observed: (a) a decrease of height standard deviation scores (SDS) (from 1.5+/-1.7 to 0.9+/-1.3 SDS, P<0.01); (b) a striking deceleration of bone age (BA), revealed by the subnormal DeltaBA:Deltachronological age (CA) ratio (0.2+/-0.1); (c) an increase of predicted adult height (from 155.6+/-7.0 to 160.7+/-6.7 cm, P<0.0005). Treatment interruption was followed by an important catch-down growth, with an FH (158.4+/-5.8 cm) lower (P<0.025) than that predicted at the end of therapy. However, FH fell within the population norm and the target range in respectively 87.3 and 90% of the patients. The tallest FH was recorded in the patients who started therapy at less than 6 years of age and in those who discontinued treatment at a BA of 12.0--12.5 years. At stepwise regression analysis, FH in the whole study population was positively affected by the following independent factors: (a) height at the end of therapy (F=45.45, P<0.0001); (b) pretreatment height (F=13.91, P<0.0005); (c) treatment duration (F=8. 51, P<0.005); (d) target height (TH) (F=7.70, P<0.01). We conclude that: (i) most girls with idiopathic CTPP treated by GnRH agonists may achieve an adult height within the population norm and/or their target range; (ii) the height gain from therapy onset until FH attainment, however, is generally rather limited (on average 2.9 cm) and only few patients are able to reach their target percentile; (iii) the most favorable height prognosis with respect to TH is generally observed in the subjects with the tallest height at the end of treatment and the lowest BA2:CA2 ratio, due to the important deterioration of height prognosis which frequently follows therapy interruption; (iv) FH is also significantly conditioned by both TH and treatment duration; (v) in order to strengthen the weak therapeutic effect of GnRH agonists in CTPP this treatment should be started as early as possible and discontinued at a BA of 12.0--12.5 years.