Influence of biochemical diagnosis of growth hormone deficiency on replacement therapy response and retesting results at adult height.

Isolated growth hormone deficiency (IGHD) is the most frequent endocrinological disorder in children with short stature, however the diagnosis is still controversial due to the scarcity of reliable diagnostic criteria and pre-treatment predictive factors of long term-response. To evaluate recombinant growth hormone (rGH) long-term response and retesting results in three different groups of children divided in accordance with the biochemical criteria of initial diagnosis. Height gain (∆HT) at adult height (AH) and retesting results were evaluated in 57 rGH treated children (M = 34, 59.6%) divided into 3 groups according to initial diagnosis: Group A (n = 25) with max GH peak at stimulation test < 8 µg/L, Group B (n = 19) between 8 and 10 µg/L and Group C (n = 13) with mean overnight GH < 3 µg/L (neurosecretory dysfunction, NSD). Retesting was carried out in all patients after at least one month off therapy upon reaching the AH. 40/57 (70.2%) patients were pre-pubertal at diagnosis and showed ∆HT of 1.37 ± 1.00 SDS, with no significant differences between groups (P = 0.08). Nonetheless, 46% patients in Group B showed ∆HT < 1SDS (vs 13% and 12% in Group A and C, respectively) and 25% children failed to reach mid-parental height (vs 6% and 0% in Group A and C, respectively). At AH attainment, IGHD was reconfirmed in 28% (7/25) and 10% (2/19) in Group A and B, respectively. A reduction of diagnostic cut-off at GH stimulation tests could better discriminate between "good" and "poor responders" and predict the persistence of IGHD through transition. Group C response and the predictive value of baseline IGF-I SDS bring back to light NSD: should we consider an underlying hypothalamic derangement when the clinical presentation is strongly consistent with IGHD but pharmacological stimulation test is normal?