Precocious puberty is the early development of any secondary sexual characteristics: before the age of nine years in a boy and eight years of age in a girl.
What is precocious puberty?
Developing the physical changes associated with puberty unusually early is known as precocious puberty.
In a girl, these changes are the development of breasts, pubic and/or armpit hair before eight years of age, or starting periods (menarche) before nine years of age.
In a boy, the changes are enlargement of the testicles, scrotum and penis and development of pubic and armpit hair before nine years of age.
What causes precocious puberty?
Hormones are chemicals produced by specialised endocrine glands. In normal puberty, hormones from an area of the brain called the hypothalamus signal to the pituitary gland (a small gland situated underneath the brain) via a hormone called gonadotrophin-releasing hormone to produce hormones known as gonadotrophins (luteinising hormone and follicle stimulating hormone). These gonadotrophins in turn stimulate the sex glands (testicles in boys and ovaries in girls) to produce sex hormones. These hormones are mainly testosterone in boys and oestrogen in girls and they stimulate the development of the physical signs of puberty. In precocious puberty, there is early activation of nerve cells in the hypothalamus producing gonadotrophin-releasing hormone or excess gonadotrophin production from the pituitary gland as a result of a pituitary tumour. In both cases, the pattern of pubertal development is usually normal, but premature or precocious.
The cause of precocious puberty related to early increases in activity of the hypothalamus is usually unknown although underlying causes are occasionally found in girls and in up to 50% of boys. The causes may include excess fluid (hydrocephalus) after head trauma or radiotherapy, and both benign and also malignant brain tumours.
There are other rare forms of early sexual development. Puberty is not always due to premature activation of the hypothalamus or excess gonadotrophin hormone production. These rare forms include early breast development without the development of other secondary sexual characteristics (premature thelarche), an increased production of androgens from the adrenal cortex (adrenarche) causing premature development of pubic and armpit hair and overproduction of testosterone due to a geneticmutation in the signalling of gonadotrophins. McCune Albright syndrome is also associated with precocious puberty, due to an underlying defect in the ovaries or testes.
What are the signs and symptoms of precocious puberty?
In girls, the first sign of precocious puberty is the development of breast tissue followed by pubic and armpit hair, along with a growth spurt and the beginning of menstruation (menarche).
In boys, the first sign is enlargement of the testicles followed by growth of the penis along with pubic and armpit hair development. The growth spurt in boys doesn’t occur until mid-puberty.
How common is precocious puberty?
Precocious puberty is probably relatively common because the definition is based on what is considered to be the normal age ranges for puberty. This is especially the case because the age of puberty has reduced over recent generations and it is recognised that puberty is earlier in certain ethnic groups such as Afro-Caribbean and South Asian.
According to 1997 data, an estimated 4-5% of girls from all racial groups had precocious puberty. Although figures for boys are unknown, they are likely to be much lower.
There are also other conditions where some features of puberty can occur early. These are often referred to as premature sexual maturation because it is the development of just one feature of puberty and not all features of puberty which occur in an orderly manner. Although, these occur early, the pattern of puberty is usually different from normal. Some are very common and are considered just variations of normal puberty, eg, isolated breast development in a female infant (isolated thelarche).
Is precocious puberty inherited?
Precocious puberty does tend to run in families, so if a parent or a sibling has gone into puberty early without an underlying cause, the chances are increased.
How is precocious puberty diagnosed?
Any child with precocious puberty should be referred to a specialist. The diagnosis of precocious puberty is initially based on:
- A careful history and examination
- Accurate measurement of height, including body proportions and weight
- Bone age estimation (usually more advanced than the age of the patient)
- Blood tests to measure appropriate hormones
The blood tests may be single (baseline) ones carried out in an outpatient department or require day case admission for stimulation testing. An X-ray of the left wrist is also often also performed at the first outpatient appointment to assess how much remaining growth there is, producing a ‘biological age’ or bone age. Girls will often have a pelvic ultrasound scan to look at the ovaries and womb (uterus). A magnetic resonance imaging scan (MRI) of the brain is routinely performed if precocious puberty is confirmed and, if there is a suggestion of an underlying disorder, then additional tests are required.
How is precocious puberty treated?
Exact treatment depends on the individual and on how early puberty has started. For some children, it may be felt that the best course of action is for no treatment to be given.
If a child is felt to have precocious puberty and require treatment, puberty can be blocked by regular injections of a drug that stops the production of gonadotrophins from the pituitary gland, usually given every six to ten weeks. This acts on the hypothalamus to stop it producing gonadotropin-releasing hormone. Once the injections stop, the child will usually progress through puberty normally.
If the cause of precocious puberty is independent of gonadotrophin-releasing hormone then the precocious puberty can be treated with drugs that stop the production or action of oestrogen or testosterone.
Are there any side-effects to the treatment?
These are mild side-effects like headaches, mood changes, weight gain, rashes and local irritation. Some girls may experience some vaginal bleeding early in the treatment as when the gonadotropin-releasing hormone agonists start working.
What are the longer-term implications of precocious puberty?
Although children who undergo precocious puberty are often initially taller and more mature looking than their peers, the fixed amount of growth in puberty can result in untreated children ending up significantly shorter as adults. However, this does depend on how early puberty starts and children with only a slightly early puberty do not end up shorter than normal.
Children who reach puberty early are exposed early to sex hormones and may also have a different body image from their peers who have not yet reached puberty. This may lead to behavioural problems due to the fact that they may be treated as older than they actually are.