Endocrine Abstracts

Introduction: Testotoxicosis, also known as familial male limited precocious puberty, is a rare cause of peripheral precious puberty caused by an activating mutation of the gene encoding for the LH receptor on Leydig cells (LHCGR gene, cr2p21). This causes autonomous testosterone production irrespective of prepubertal LH values. Ultimately, this can cause psychosocial complications; advanced bone age and low adult height; as well as central precocious puberty.

Case report: We present the case of a 5 year, 8 month old boy that was directed to the Endocrinology Clinic because of increased testicular volume, penile enlargement, and the presence of scrotal, pubic and upper lip hair. Family history was negative for precocious puberty. Clinical examination revealead a height of 119 cm (-0.42 SD) and weight of 20 kg, BMI 14.2 kg/m² (normal), Tanner stage 2; and wrist X-ray showed a bone age of 5 years and 6 months. Hormonal evaluation revealead a testosterone level more than 10 times the upper limit of normal for age and sex (7.22 nmol/l), with low FSH and LH levels (0.411 mIU/ml and 0.146 mIU/ml, respectively), even after Triptorelin stimulation (2.33 mIU/ml and 2.68 mIU/ml, respectively). Low 17OH-progesterone levels ruled out congenital adrenal hyperplasia. Testicular or adrenal tumors were excluded based on negative tumor markers and imaging studies; while McCune Albright syndrome and iatrogenic PPP were excluded based on history and physical examination. Therefore, testotoxicosis was diagnosed by exclusion, and treatment with aromatase inhibitors (anastrozole, 0.1 mg/day) and bicalutamide (25 mg/day) was initiated. At 3 month follow-up, no side effects were reported except for mild headache occasionally, and there was regression of pubertal signs. Gonadotropin levels remained low, while elevated testosterone persisted; and bone X-ray didn’t demonstrate advancement of bone age. At the moment, genetic studies are underway to identify the causing mutation.

Conclusion: Testotoxicosis is a rare form of PPP, and the limited studies available suggest optimal treatment is with a combination of aromatase inhibitors and antiandrogen medications. Testosterone levels shouldn’t be used as a marker for treatment efficacy, as elevated levels can persist; but rather focus should be on gonadotropin levels and decreasing the bone age to chronological age ratio, if advanced at diagnosis. Finally, genetic studies of the child and both parents should be carried out whenever possible, as the causing mutation is usually inherited in an autosomal dominant manner, and females can be asymptomatic carries, but de novo mutations can also occur in previously unaffected families.