Disorders of the pituitary gland are relatively rare.
What is the most common disorder?
The most common cause of pituitary malfunction is a benign tumour (adenoma)
Most pituitary tumours are “non-functioning”.
What does this mean?
Non-functioning pituitary tumours contain tumour cells which themselves do not produce any hormone
What is the usual consequence of non-functioning pituitary tumours?
These tumours can result in inadequate production of 1/more pituitary hormones due to physical pressure from the growing tumour on glandular tissue
What are the clinical symptoms of non-functioning pituitary tumours?
Pressure on surrounding structures in the vicinity of the tumour result in:
- Visual problems (optic nerve)
Functional pituitary tumours are quite rare.
What does this mean?
Hypersecreting (functional) pituitary tumours contain tumour cells involved in the overproduction of 1/more of the pituitary hormones
What are the clinical symptoms of functional tumours?
The clinical symptoms of hypersecreting tumours usually correspond to the systemic effects of the over secreted hormone
Outline the clinical approach in the investigation of a suspected pituitary tumour
- Delineation of the anatomy, size and topographical location of pituitary / parapituitary mass (MRI scan)
- Assessment of visual field defects
- Assessment of endocrine function to determine hormonal excess/deficiency
How might one assess the endocrine function in a patient with a suspected pituitary tumour?
- Measure hormone levels in blood
- Staining sections from a biopsy of the tumour with antibodies for the relevant hormone
What is hypopituitarism?
Hypopituitarism is a state of insufficient pituitary hormone production, commonly due to a pituitary adenoma and rarely due to radiation therapy, inflammatory disease or head injury
In light of hypopituitarism, what is the consequence of the adenoma?
Progressive loss of anterior pituitary function (GH and LH/FSH first)
What is panhypopituitarism?
Panhypopituitarism is the deficiency of all anterior pituitary hormones
Why aren't ADH and oxytocin secretion usually impaired in hypopituitarism?
Secretion of ADH and oxytocin from the posterior pituitary is usually only significantly affected if the tumour affects hypothalamic function
What are some causes of GH deficiency?
- Mass defects from pituitary adenoma
- Specific gene mutations e.g. GH-releasing hormone receptor
- Autoimmune inflammation
What are the symptoms of GH hormone deficiency secondary to mass defects from a pituitary adenoma?
- Decreased tolerance to exercise
- Decreased muscle strength
- Increased body fat
- Reduced sense of “well-being"
Why is GH deficiency often difficult to diagnose?
GH secretion is pulsatile, deficiency is often difficult to diagnose and a combination of direct and indirect measurements are required
What are the symptoms of Gonadotropin deficiency in men and women secondary to mass defects from a pituitary adenoma?
- Women – infertility, oligomenorrhea, amenorrhea, lack of libido
- Men – impotence, lack of libido
What are some causes of ADH deficiency?
- Hypothalamic tumour
- Extension of pituitary tumour
- Cranial radiotherapy
- Pituitary surgery
- Autoimmune infiltration
- Infections e.g. meningitis
What is the main consequence of ADH deficiency?
Diabetes insipidus – excess excretion of dilute urine resulting in dehydration and an increased sensation of thirst (polydipsia)
What is hyperpituitarism?
Hyperpituitarism is a state of excess pituitary hormone production mainly due to a functional hypersecreting pituitary adenoma
There are three main conditions caused by excess pituitary hormone production from a hypersecreting pituitary adenoma.
- Prolactin excess
- Growth hormone access
- ACTH excess
Hyperprolactinaemia is the most common form of pituitary disorder and can cause a range of symptoms.
Identify five of these
- Galactorrhea (unexplained milk production – rare in men)
- Gynecomastia (hard breast tissue)
- Hypogonadism (diminished activity of testes or ovaries)
- Amenorrhea (cessation of menstrual cycle)
- Erectile dysfunction
What is the most common cause of hyperprolactinaemia?
Prolactinoma – a pituitary adenoma that secretes prolactin
Identify some physiological causes of hyperprolactinaemia
- Drugs (antipsychotics & antidepressants)
In four steps, explain how hypogonadism arises as a co-morbidity in hyperprolactinaemia
⇒ Increased plasma prolactin
⇒ Higher level of dopamine for negative feddback
⇒ Dopamine inhibits GnRH secretion from hypothalamus
⇒ FSH and LH secretion from the anterior pituitary inhibited
How is hyperprolactinaemia usually treated?
- Dopamine receptor agonists e.g. cabergoline
- Trans-sphenoidal surgery (rare)
- Radiotherapy (rare)
Growth hormone secreting pituitary adenomas are typically large (>10 mm in diameter).
In light of this, identify some of its associated symptoms
- Local mass effects – headache, visual field defects and other cranial nerve palsies
- Systemic effects – increased GH secretion & local IGF-1 production leads to gradual change in physical appearance
Describe some the the changes in physical characteristics observed in growth hormone excess
- Coarse facial features: broad nose, thick lips, prominent supraorbital ridge
- Enlargement of the hands and feet
- Greasy skin
- Excessive sweating
- Deepening of the voice (hypertrophy of vocal cords)
Explain why excess GH secretion can be associated with diabetes mellitus
GH antagonises the actions of insulin, so diabetes mellitus develops as a metabolic complication
Three types of treatment options are available for patients with acromegaly.
- Radiation therapy
- Drug therapy e.g. dopamine receptor agonists, synthetic somatostatin analogs
What is a consequence of excessive ACTH secretion due to a pituitary adenoma?
Excess endogenous secretion of ACTH from the anterior pituitary gland is one of the causes of Cushing’s syndrome