A 15-year-old boy has no signs of pubertal development (testicular volume 3 mL, Tanner stage I). His height is at the 25th centile. Bone age is 13 years. His sense of smell is normal. Baseline FSH and LH are low. GnRH stimulation test shows a low LH response. His father and uncle both had delayed puberty. What is the most likely diagnosis?

• A Kallmann syndrome
• B Isolated hypogonadotropic hypogonadini (normosmic) ✓
• C Constitutional delay of growth and puberty
• D Klinefelter syndrome

Explanation

Isolated hypogonadotropic hypogonadism (IHH) is normosmic and features low gonadotropins with normal smell, distinguishing it from Kallmann syndrome where anosmia is present. Constitutional delay shows delayed bone age with eventual spontaneous puberty and often short stature for age, not just low-normal. Klinefelter syndrome presents with hypergonadotropic hypogonadism (elevated FSH/LH). The normal smell rules out Kallmann syndrome.

Reference: Williams Textbook of Endocrinology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.