Role of GnRH stimulation test in prediction of a neurogenic aetiology in girls with central precocious puberty
Saravana Bhavan,Hemchand Krishna Prasad,Anupama Sankaran, Vijaykumar P Govindram,C V Ravisekar,K Nedunchelian Krishnamooorthy
Objective: To ascertain the utility if gonadotrophin releasing hormone (GnRH) test in diagnosis of neurogenic central precocious puberty (NCPP). Methods: We conducted a prospective observational study over a period of 4 years recruiting girls with early breast budding. Children underwent GnRH analogue stimulation test with injection luperide 20mcg/kg in subcutaneous route followed by assessment of gonadotropins (LH and FSH) at 4 hours and estradiol at 24 hours. MRI performed in everyone with CPP. Cases divided into those with neurogenic CPP (NCPP) and idiopathic CPP (ICPP). Results: During the study period, 59 girls presented with early sexual maturation; we included 19 subjects onto our study (12 girls with idiopathic central precocious puberty and 7 girls with neurogenic precocious puberty). Stimulated LH was higher in subjects with NCPP compared to those with ICPP (9.8±3.0 versus 8.4±3.6 mIU/mL, p<0.05). Stimulated LH:FSH ratio was higher in those with NCPP versus ICPP (0.5±0.3 versus 0.34±0.3, respectively). On multivariate regression analysis, stimulated LH:FSH ratio is the most likely determining factor for the occurrence of a neurogenic aetiology for central precocious puberty. ROC curve constructed to determine the optimal cut off to distinguish neurogenic and idiopathic causes of central precocious puberty. LH:FSH >0.55 is able to predict neurogenic precocious puberty with specificity of 82% and sensitivity of 66.7%. Conclusion: Elevated LH levels and LH/FSH ratio in GnRHa stimulation test gives an important clue to a possible underlying neurological pathology. A cut-off of 0.55 predicts neurogenic precocity with a specificity of 82%.