Precocious puberty is defined as the onset of any component of pubertal development and accelerated growth that occurs ≥2.5 standard deviations (SD) below the mean age for normal children.

Historically, the average age of onset of puberty in girls was approximately 10 years of age, and pubertal changes occurring before the age of 8 years (−22 SD) were considered precocious. However, the definition of precocious puberty has been contested by recent studies. The 1997 Pediatric Research in Office Settings (PROS) Network evaluated the timing of puberty in approximately 17,000 healthy young female patients. While the mean age of onset of breast development was 10.0 years in Caucasian girls, it was 8.9 years in African American girls. The National Health and Nutrition Examination Survey III (NHANES III) also reported that the average age of puberty showed notable variation among ethnic groups, with Caucasian, African American, and Mexican American girls showing pubertal changes beginning at the mean ages of 10.4, 9.5, and 9.8 years, respectively. That said, the findings of the PROS study have also been challenged because breast development was determined visually (not by palpation), mean BMI of the subjects favored overweight (increasing the likelihood of labeling fat in the chest area as true breast tissue), and no testing was performed to rule out pathologic causes in borderline cases. Furthermore, the reported time of menarche in this study was unchanged from prior data, suggesting an unexplained longer duration of puberty.

Thus, it remains unclear whether or not girls may be starting puberty earlier than previously thought, so that most authorities in the field still recommend an evaluation if changes begin prior to the age of 8 years, with careful individualization between 6 and 8 years depending on race, weight, and rate of progression of pubertal changes. While the evaluation of precocious puberty is primarily conducted by pediatric endocrinologists, the practicing obstetrician-gynecologist may be called upon to make the diagnosis. This discussion will be focused on the essentials of recognition of this condition, and its diagnosis and management.

Precocious puberty is classified into two types: 1) complete, central or gonadotropin-releasing hormone (GnRH) dependent, and 2) incomplete, peripheral or GnRH independent.

Central precocious puberty

Central precocious puberty (CPP) has also been referred to as GnRH-dependent precocious puberty. Ninety percent of all female children with precocious puberty have the central form in which there is premature activation of hypothalamic GnRH pulses causing release of gonadotropins. The etiology of CPP always involves the central nervous system (CNS). CPP is divided into two diagnostic subgroups: idiopathic and organic.

An idiopathic basis is the most common etiology for female CPP, accounting for 70% of cases. The underlying etiology for the premature activation of the hypothalamic-pituitary-ovarian axis is unknown but, regardless, the endocrine events that occur are advanced with respect to the child’s chronologic age. Children with pathologic forms of precocious puberty have a growth spurt which is early, rapid, and of shorter duration than normal. At first, they are much taller than their peers but if untreated, they may end up very short as adults due to premature epiphyseal closure. Their skeletal maturation will be reflected by a bone age that is significantly older than their chronologic age. In general, the earlier the process begins, the shorter the adult height. The onset of symptoms may occur at any age prior to 8 years, but is quite uncommon in the first few years of life. The rate of progression and the sequence of symptoms can vary greatly. Spontaneous remissions occur, but are relatively uncommon. The general health of children with idiopathic CPP is not impaired, but the pubertal changes may create emotional conflicts for both the child and her family. These children may have an increase in minor psychopathologic symptoms, but do not manifest an increase in severe psychiatric disorders. Children with idiopathic CPP may have functional follicular ovarian cysts identified by a pelvic ultrasonographic examination which are the result, not the cause, of their early puberty. Problems of infertility and premature ovarian failure are not increased in children with a history of idiopathic CPP. The diagnosis is made by excluding all other causes of precocious puberty.

Central nervous system disease is responsible for 30% of the children with CPP. The development of high-resolution imaging modalities has resulted in an increase in the identification of organic brain disease which includes hypothalamic hamartomas, congenital mid-line defects, tumors, cysts, postinfectious lesions, neurofibromatosis, and post-traumatic brain injury. Hypothalamic hamartoma is the most common CNS tumor observed in young children with CPP. The hamartoma is a benign congenital malformation typically attached to or suspended from the floor of the third ventricle, and may, on occasion, be associated with gelastic (laughing) or other seizures. Mechanisms by which hamartomas are thought to cause precocious puberty include the production of TGF-α which, in turn, stimulates GnRH release and the “ectopic” production of GnRH itself by the tumor, but in general, the cause is unknown.

All children with CPP must have a thorough evaluation, including a complete neurologic examination and magnetic resonance imaging (MRI) scan before CNS disease can be excluded. CT scans provide poor resolution of the suprasellar region and are not recommended in the evaluation of CPP. A newly recognized genetic cause of CPP involves an activating mutation of the GPR54 receptor, the ligand for which is known as kisspeptin, and the normal function of which is the activation of GnRH.

Peripheral precocious puberty

Peripheral precocious puberty (PPP) has also been referred to as GnRH-independent precocious puberty. Children with PPP do not attain cyclical function of the reproductive axis, follicular maturation, and ovulation. PPP is divided into the following diagnostic subgroups:

• ovarian tumors or cysts
  
• human chorionic gonadotropin (hCG)-producing tumors
  
• adrenal tumors
  
• exogenous sources of sex steroids
  
• primary hypothyroidism
  
• McCune–Albright syndrome

One of the major causes of PPP in the female patient is an estrogen-producing ovarian granulosa-theca cell tumor (also commonly known as a granulosa cell tumor). These tumors are almost always palpable on rectal-abdominal examination and can be identified by ultrasonography. Most granulosa-theca cell tumors are benign and are confined to one ovary. The usual treatment is unilateral salpingo-oophorectomy. Estrogen-secreting ovarian cysts may also be a cause of PPP. Germ cell tumors, in girls, may rarely secrete hCG which stimulates ovarian estrogen secretion and causes precocious puberty.