Hypopituitarism
Hypopituitarism is an uncommon disease in which one or more of the hormones produced by the pituitary gland is lacking. The pituitary gland is the body's “master gland” and is located in the brain. Hormones produced by the anterior lobe of the pituitary gland include thyroid stimulating hormone (TSH), growth hormone (GH), adrenocorticotropic hormone (ACTH), the gonadotropins, luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin. The posterior lobe of the pituitary gland produces the hormones antidiuretic hormone (ADH) and oxytocin.
| Hormone | Function |
| TSH | Stimulates the thyroid to produce thyroxine; deficiency leads to hypothyroidism with symptoms of tiredness, constipation, weight gain, slowed heart rate and in children slow growth |
| GH | In children, this is important for linear growth; deficiency leads to decrease in muscle mass, central obesity and growth retardation in children |
| ACTH | Stimulates production of glucocorticoids; deficiency leads to fatigue, hypoglycemia (low blood sugar), hyponatremia (low sodium levels), low blood pressure and failure to thrive in children |
| LH, FSH | Stimulates pubertal development leading to estrogen production in girls and testosterone production in boys. Children with deficiency in gonadotropins may have delayed or absent puberty. Adolescents and adults with LH, FSH deficiency may have abnormal menstrual cycles, infertility, decreased sexual function and osteoporosis. |
| Prolactin | Stimulates breast-milk production; deficiency may lead to difficulties with breastfeeding |
| ADH | Stimulates kidneys to concentrate urine and body to retain water; deficiency leads to diabetes insipidus in which frequent urination and extreme thirst occur |
| Oxytocin | Stimulates uterine contractions during child-birth |
Causes of hypopituitarism
Congenital hypopituitarism occurs when hormone deficiencies are present at birth and is often the result of under-development of the pituitary gland. There are several known genetic abnormalities that lead to decreased function of the gland.
One cause of congenital hypopituitarism is septo-optic dysplasia, a disease in which there is under-development of the optic nerves (leading to decrease vision and often suspected by nystagmus or “wandering eyes”), pituitary gland and other structures in the brain. Children with septo-optic dysplasia have varying degrees of hypopituitarism, commonly diabetes insipidus and growth hormone deficiency.
Other forms of congenital hypopituitarism are characterized by growth hormone deficiency, adrenal insufficiency and hypothyroidism. Kallman syndrome causes deficiency of only gonadotropins and is often associated with a decreased ability to smell.
Brain tumors are another cause of hypopituitarism. These tumors may arise from within the pituitary gland, or they may grow outside the gland and compress the normal tissue. Often, it is the hormonal disturbances from these tumors that lead to diagnosis of the tumor by brain imaging scans. Often the hormonal deficiencies are permanent following surgical removal of the tumor.
There are other rare causes of hypopituitarism and these include brain infection, traumatic brain injury, radiation to the brain and bleeding into the gland. In children, the most common causes of hypopituitarism are congenital and the presence of a brain tumor.
Diagnosis of hypopituitarism
The diagnosis of hypopituitarism consists of blood tests and brain imaging with an MRI. Obtaining a blood test in the morning is preferable as hormone levels fluctuate throughout the day. Stimulation tests are often necessary to diagnose specific hormone deficiencies if the morning blood tests are not diagnostic. A water deprivation test may be necessary to diagnose diabetes insipidus. A brain MRI scan is performed if any of the hormone tests are abnormal or if the patient's symptoms are consistent with hypopituitarism.
An MRI scan will identify a tumor or other developmental abnormalities in the pituitary gland.
Treatment
Treatment involves identifying the underlying cause of hypopituitarism and replacing the hormones that the body is no longer making. For example, some tumors respond to medications by mouth while others require surgical removal. Pituitary hormones are replaced to mimic the body's natural production. Hydrocortisone must be administered 2 to 3 times daily for adrenal insufficiency. During illness or surgeries, a “stress dose” of hydrocortisone needs to be given in addition to the daily replacement. Levothyroxine is given daily for hypothyroidism. Growth hormone, in the synthetic form, must be administered as an injection daily. Antidiuretic hormone is replaced by desmopressin (dDAVP) either as a tablets or a nasal spray. However, infants with diabetes insipidus are treated with chlorothiazide, a medication given by mouth that helps infants to reduce their large urine output. Patients with low gonadotropin levels need replacement of estradiol in girls and testosterone in boys. Girls also require progesterone replacement once their puberty development is near completion.
Along with appropriate hormone replacement, patients with hypopituitarism need frequent monitoring to evaluate growth and development. Dose adjustments during childhood are necessary to accommodate the growing child's needs and changes in symptoms.
In summary, hypopituitarism is rare in children. However, appropriate diagnosis and treatment with hormone replacement will improve the child's quality of life.