Lecture 6.2 - Pituitary disorders

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Questions and Answers

What is the primary cause of the nephrogenic form of diabetes insipidus?

Dopamine deficiency

ADH deficiency

ADH resistance (correct)

Pituitary stalk obstruction

What is the primary difference between a macro-adenoma and a micro-adenoma?

Age of onset

Type of hormone secreted

Location within the pituitary gland

Size of the tumour (correct)

What is the typical treatment for a prolactinoma?

Medication with dopamine agonists (correct)

Surgical removal of the tumour

Radiotherapy

Hormone replacement therapy

What is the significance of a prolactin level above 5000 miU/L?

Likely due to active prolactin secretion Signup and view all the answers

What is the primary function of dopamine in regulating prolactin?

Inhibiting prolactin secretion Signup and view all the answers

What is a common symptom of hyperprolactinaemia in women?

Galactorrhoea Signup and view all the answers

What is the incidence of GH deficiency in live births?

1 in 3800 Signup and view all the answers

What is the primary cause of hypogonadism due to mass effects from a pituitary adenoma?

Gonadotropin deficiency Signup and view all the answers

What is the characteristic symptom of TSH deficiency?

All of the above Signup and view all the answers

What is the primary function of antidiuretic hormone (ADH)?

Regulation of water reabsorption in the kidneys Signup and view all the answers

What is the primary cause of diabetes insipidus in pituitary tumours?

Extension of the pituitary tumour into the hypothalamus Signup and view all the answers

What is the effect of severe prenatal GH deficiency?

Hypoglycaemia and jaundice Signup and view all the answers

What is the primary treatment for GH deficiency in children?

Human recombinant GH Signup and view all the answers

What is the effect of ACTH deficiency on the body?

Decreased cortisol levels Signup and view all the answers

What is the most common cause of pituitary disorders?

Benign tumor (adenoma) Signup and view all the answers

What is the primary effect of a non-functioning pituitary tumor on pituitary hormone secretion?

No effect on pituitary hormone secretion Signup and view all the answers

Which of the following cranial nerves is NOT affected by the mass effect of a pituitary tumor?

VII nerve (facial movement) Signup and view all the answers

What is the primary purpose of measuring hormone levels in the blood during the investigation of a suspected pituitary tumor?

To determine whether there is a hormonal excess or deficiency Signup and view all the answers

What is the typical order of pituitary hormone secretion loss in hypopituitarism?

GH and LH/FSH, followed by ACTH and TSH Signup and view all the answers

What is the primary symptom of growth hormone deficiency in adults?

Reduced sense of wellbeing Signup and view all the answers

What is the primary effect of a pituitary tumor on the posterior pituitary?

No effect on posterior pituitary function Signup and view all the answers

What is the primary purpose of performing an MRI scan during the investigation of a suspected pituitary tumor?

To determine the size and location of the tumor Signup and view all the answers

What is the primary type of pituitary tumor that causes hyperprolactinaemia?

Prolactinoma Signup and view all the answers

What is the primary symptom of diabetes insipidus?

Polyuria Signup and view all the answers

Study Notes

Diabetes Insipidus

Diabetes insipidus is caused by ADH resistance, where the kidneys do not respond to ADH in the normal way.
It should not be confused with diabetes mellitus.

Prolactinoma

Prolactinoma is a prolactin-secreting pituitary tumor.
Macro-adenoma refers to a large tumor (>1cm), while micro-adenoma refers to a small tumor (<1cm).
The larger the prolactinoma, the higher the prolactin levels.
Prolactinomas are typically treated with tablets, even in cases where the tumor is large and causes visual problems.
Prolactin is under tonic inhibitory control by dopamine, so anything blocking the pituitary stalk will lead to prolactin disinhibition.
If prolactin levels are <5000 miU/L, it may be due to disinhibition rather than active prolactin secretion.
If prolactin levels are >5000 miU/L, it is likely due to active prolactin secretion (prolactinoma).

Symptoms of Hyperprolactinaemia in Women

Galactorrhoea (unexplained milk production - milky discharge from breasts)
Menstrual disturbance

Growth Hormone Deficiency

Growth hormone (GH) deficiency has little effect on fetal growth.
Severe prenatal deficiency can result in hypoglycaemia and jaundice.
From ~1 year of age until mid-teens, GH deficiency results in poor growth and short stature (treatment: human recombinant GH).

Gonadotropin Deficiency

Gonadotropin deficiency in adults can result in:
- Loss of secondary sexual characteristics
- Lack of libido, infertility, and oligomenorrhea or amenorrhea in women of reproductive age
- Decreased libido and impotence in men
In children, gonadotropin deficiency can result in delayed puberty.

TSH and ACTH Deficiency

TSH deficiency can result in:
- Low thyroid hormones (low T4)
- Non-elevated TSH
- Symptoms: feeling cold, weight gain, tiredness, slow pulse
ACTH deficiency can result in:
- Low cortisol
- Symptoms: feeling tired, dizzy, low blood pressure (low sodium)
- HPA axis integrity is vital, so ACTH deficiency can be life-threatening.

ADH Deficiency (Diabetes Insipidus)

ADH deficiency may result from a hypothalamic tumour or a pituitary tumour that has extended up into the hypothalamus.
Other causes of ADH deficiency: cranial radiotherapy, pituitary surgery, autoimmune infiltration, and infections such as meningitis.
Insufficient release of ADH from the posterior pituitary leads to:
- Excess excretion of dilute urine
- Dehydration
- Increased sensation of thirst (polydipsia)

Pituitary Gland

The pituitary gland sits below the brain in the sella turcica (a pocket of the sphenoid bone).

Pituitary Disorders

Pituitary disorders are relatively rare (~70,000 patients in the UK).
They manifest as either OVER or UNDER secretion of pituitary hormones.
The most common cause is a benign tumour (adenoma).

Clinical Presentation of Pituitary Tumours

Most pituitary tumours are "non-functioning" (the tumour cells do not produce any hormone).
Mass effect of tumour on local structures:
- Visual loss
- Headache
Abnormal pituitary function:
- Hypo-secretion of pituitary hormones
- Hyper-secretion of pituitary hormones
Mass effect of pituitary tumour on local structures:
- Optic chiasm (vision loss)
- III, IV (eye movement)
- Va,b (pain)
- Internal carotid artery (blood supply)
- VI nerve (lateral eye movement)

Investigation of a Suspected Pituitary Tumour

Imaging: size and topographical location of the pituitary or parapituitary mass (usually by MRI scan).
Assessment of visual field defects.
Assessment of endocrine function to determine whether there is a hormonal excess or deficiency.
Measuring the levels of relevant hormones in the blood (where possible staining sections from a biopsy of the tumour with antibodies for the relevant hormone).

Hypopituitarism

Hypopituitarism is insufficient production of pituitary hormones.
Most commonly a result of a pituitary adenoma (rarer causes include radiation therapy, inflammatory disease, and head injury).
Loss of pituitary hormone secretion is usually secondary to a mass effect of the adenoma.
Typically progressive loss of anterior pituitary function (GH and LH/FSH are usually the first hormones to be affected).
Pan-hypopituitarism: deficiency for ALL anterior pituitary hormones.
Secretion of antidiuretic hormone (ADH) and oxytocin from the posterior pituitary is usually affected significantly only if the tumour affects the hypothalamic function or if an inflammatory process is involved.

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Test your knowledge of endocrine disorders, including diabetes insipidus and prolactinoma, their causes, and treatment options.