SAT-298 A Case of a Forgotten Histrelin Acetate Implant: Can Histrelin Acetate Implants Be Used for More Than a Year?

Introduction The Histrelin acetate implant (50 mg) has been used widely in the treatment of central precocious puberty (CPP). The implant is inserted subcutaneously and provides continuous release of gonadotropin releasing hormone analog (GnRHa) Histrelin. It provides pubertal hormonal suppression for 1 year and needs to be replaced yearly. We present an interesting case of a forgotten Histrelin implant which was not removed for 5 years. Clinical Case 7 years and 0-month-old, healthy female presented to Endocrine clinic with breast and pubic hair development. On physical exam, she was noted to have Tanner III breasts and Tanner II pubic hair. Initial labs revealed LH - <0.1 mIU/mL [<0.2], FSH - 1.6 mIU/mL and Estradiol <20 [<20]. Thyroid function test and electrolytes were normal. Bone age done by primary care provider at 6 years and 6 months revealed a bone age of 8 years and 10 months. Ultrasound of pelvis revealed bilaterally enlarged ovaries due to multiple follicles and adrenals were normal. Leuprolide stimulation test revealed peak LH at 4.6 mIU/mL, FSH at 18.3 mIU/mL and Estradiol - 169 pg/mL which were consistent with CPP. Brain MRI was within normal limits. Her repeat bone age at chronological age 7 years and 6 months was advanced at 11 years. She was started on Leuprolide depot injections and later had a Histrelin acetate implant inserted in the left arm. Labs done 3 months after the implant showed hormonal suppression. She was lost to follow up about 9 months after implant insertion. She presented again to clinic 4 years and 11 months after implant was inserted for removal. Her breast development showed little progression at Tanner III breasts and Tanner IV pubic hair and she did not develop menarche yet. Her recent labs were LH 0.33 mIU/mL, FSH 1.97 mIU/mL, and Estradiol 20 pg/mL. Her bone age at chronological age of 12 years and 9 months was 13 years and 0 months. Ultrasound of left upper extremity revealed cylindrical foreign body, in the left medial upper arm superficial soft tissues. Implant removal was performed by surgical team and the implant came out in several pieces but there were no palpable remains. Discussion This patient showed very little pubertal and bone age progression over the 5-year period when she had the implant. Patients should be warned about the risks of keeping the implant longer than longer than recommended including continued suppression of the pituitary-gonadal axis and difficulty in removal of the implant. The 50 mg Histrelin implant is released at 65 mcg per day which cumulatively adds up to 23.7 mg a year. In theory, the implant would be able to release GnRHa for more than 2 years. A prospective study had shown that a single Histrelin implant is effective for 2 years in the treatment of CPP with adequate hormonal suppression. Conclusion Further studies are needed to evaluate use of the histrelin implant for more than a year which would reduce cost and decrease the number of surgical procedures.