A 6-year-old Caucasian girl is brought to your office by her mother. The mother says that her daughter is "womanly," including being exceptionally tall for her age. Physical examination reveals Tanner Stage 3 breast development and coarse pubic hair. The child's height is in the 96th percentile. You explain to her mother that, although this girl is very tall now, she will ultimately be shorter than average if she does not get treatment. Which of the following is the physiologic explanation for the information you provided?

Question

A 6-year-old Caucasian girl is brought to your office by her mother.  The mother says that her daughter is "womanly," including being exceptionally tall for her age.  Physical examination reveals Tanner Stage 3 breast development and coarse pubic hair.  The child's height is in the 96th percentile.  You explain to her mother that, although this girl is very tall now, she will ultimately be shorter than average if she does not get treatment.  Which of the following is the physiologic explanation for the information you provided?

Quizplus · Accepted Answer

The child described in the vignette is six years old and has already undergone pubertal changes, as indicated by her Tanner staging. (Also called the sexual maturity rating, Tanner staging is a systematic, universalized method that uses female breast and pubic hair development to categorize development.) Precocious puberty in Caucasian females is defined as the development of secondary sexual characters at an age less than seven years. Young bone has several layers; their order from middle to end is diaphysis, metaphysis, epiphyseal cartilage, and epiphysis. The epiphyseal cartilage, also called the "growth plate, is responsible for linear growth. Linear growth stops when the epiphyseal growth plate closes, i.e. when the epiphysis fuses with the metaphysis. Sex steroids initially increase linear growth, but they also encourage closure of epiphyseal growth plates. Once the growth plates have closed, linear growth is irreversibly stopped. In normal puberty, there is a rapid increase in growth. At the end of this pubertal growth spurt, almost 90% of the final height is achieved. Although this child is currently taller than her peers, the excess steroids will soon cause epiphyseal growth plate closure; hence, if this patient is not treated, she will ultimately not meet her full growth potential. (Choices A and B) In sites other than the epiphyseal growth plate, the effect of estrogen on bone is anabolic because estrogen increases osteoblastic bone deposition and decreases osteoclastic bone resorption. Low estrogenic states, such as menopause, are associated with rapid bone loss. (Choices D and E) The secretion of somatomedin C, more commonly known as insulin-like growth factor-1 (IGF-1), is directly increased when growth hormone is secreted from the pituitary gland. IGF-1 causes the differentiation and proliferation of chondrocytes in the epiphyseal growth plate, causing an increase in linear growth. However, unlike estrogen, IGF-1 does not accelerate epiphyseal closure. Educational Objective: Sex hormones promote both growth and epiphyseal plate closure; hence, precocious puberty may result in a shorter stature, despite an initial growth spurt. Gigantism is caused by excessive pituitary production of growth hormone; these patients achieve enormous heights because, unlike excessive sex steroids, excessive IGF-1 does not lead to premature closure of the epiphysis.

A 6-Year-Old Caucasian Girl Is Brought to Your Office by Her