Abstract
Klinefelter syndrome (KS) is a chromosomal disorder characterized by the presence of an extra X chromosome in males (47, XXY). Individuals with KS often exhibit a range of physical, cognitive, and behavioral symptoms, including tall stature, gynecomastia, reduced libido, and varying degrees of infertility. A major diagnostic challenge arises when individuals with KS exhibit symptoms that are obscured by comorbid conditions, such as opioid use disorder (OUD). Individuals with OUD or psychiatric disease may exhibit symptoms similar to those of KS. Misattribution of symptoms can lead to delayed or missed diagnosis of Klinefelter's syndrome, underscoring the importance of a thorough evaluation, particularly in the presence of substance use disorders. In this case report, we illustrate the diagnostic challenges posed by OUD in a 39-year-old male patient with a unique case of undiagnosed KS.