6597 An Unusual Case of Klinefelter Syndrome with Both Primary and Superimposed Secondary Hypogonadism

Abstract Disclosure: A. Krueger: None. E. Pelley: None. Introduction: Klinefelter syndrome (KS) (47, XXY) is a sex-chromosome disorder that is a common cause of infertility and hypogonadism in men. Clinical phenotype includes tall stature, delayed or incomplete puberty, small testes (<4ml), gynecomastia, and oligo or azoospermia. The extra X chromosome leads to fibrosis and hyalinization of seminiferous tubules resulting in impaired sperm production. Leydig cells also function abnormally and fail to stimulate with LH. Common biochemical evaluation results in low serum testosterone, elevated FSH and LH concentrations, and azoospermia. Case Report: 37-year-old male presented with long standing history of low libido and a perception that he had never fully progressed through puberty. Physical exam was notable for a height of 6’ 4”, obesity, fine pubic and axillary hair, and testes <4mL bilaterally. Initial biochemical work up revealed low serum total testosterone 43 (ref 300-1080 ng/dL), low free testosterone 8.1 (ref 47-244 pg/mL), inappropriately normal LH 10.8 (ref 0.6-12.1 mlU/mL), and elevated FSH 28.3 (ref 1.0-12.0 mlU/mL). Patient was referred to Endocrinology. Labs were repeated with consistent results in addition to chromosome analysis which confirmed diagnosis of Klinefelter syndrome with (47, XXY) karyotype. Due to inappropriately normal LH and mixed picture of primary and superimposed secondary hypogonadism, an MRI of the pituitary was obtained and revealed an 8mm x7mm x 14mm pituitary macroadenoma. Evaluation for pituitary hypersecretion and other deficiencies was unremarkable. Conclusion: Data from the Danish National registry shows that only 25% of Klinefelter patients are correctly diagnosed. Klinefelter syndrome should be considered in the differential for the evaluation of hypogonadism and infertility. Diagnosis can be made by karyotyping. The degree of impaired spermatogenesis and testosterone production in Klinefelter syndrome can be variable. Biochemical evaluation should be interpreted in conjunction with clinical context. Patients with known causes of primary hypogonadism who demonstrate an inappropriate gonadotropin response require evaluation for causes of secondary hypogonadism. In this case, the inappropriately normal LH was the sole clue leading to the identification of his pituitary macroadenoma. Presentation: 6/1/2024