A 16-year-old girl has not yet reached menarche. She has normal secondary sex characteristics, and vi¬sual inspection of her external genitalia is unremark¬able. The patient is given progesterone and has with¬drawal bleeding a few days later. This patient most likely has

The patient most likely has a delayed onset of puberty rather than a destructive lesion in the hypothalamic/pituitary axis, a primary disease involving the ovaries or a problem involving the end-organs (e.g., imperfo­rate hymen). Note that she has normal secondary sex characteristics indicating the presence of estrogen. She had withdrawal bleeding after being given progester­one, which proves that the endometrial mucosa has already been primed with estrogen. In addition, a normal menstrual flow implies the absence of an end organ defect preventing menses from occurring. Primary amenorrhea refers to the absence of men­struation by age 16 years. As a general rule, amenorrhea is the hallmark for hypogonadism, assuming that no end-organ abnormalities are present. As with second­ary amenorrhea, primary amenorrhea is subdivided on the basis of gonadotropin levels (follicle stimulating hormone and luteinizing hormone ). Amenorrhea in the presence of elevated gonadotropins is designated as hypergonadotropic hypogonadism (primary ovarian disease), while reduced gonadotropin levels is called hypogonadotropic hypogonadism (hy­pothalamic/pituitary disease). Normal levels of FSH and LH in the presence of normal secondary sex char­acteristics usually indicate an end-organ abnormality. Absence of secondary sex characterisitics by age 16 years is always a more significant finding than having a patient with normal secondary sex characteristics. In addition to ordering gonadotropin levels, a pro­gesterone challenge is an excellent test to perform in the initial evaluation of these patients. The absence of menses confirms that there is a problem, but it does not differentiate among the three main areas previously cited. Withdrawal bleeding indicates that the endometrial mucosa must have been primed with estrogen, so the hypothalamic/pituitary axis and ova­ries must be normal. This test also rules out an end­organ defect. The following chart (partial list) provides a classification for these subdivisions of primary amen­orrhea.