Hypersecretion of Anterior Pituitary Hormones Flashcards
What is hyperpituitarism
Symptoms associated with excess production of adenohypophyisal hormones
Describe the causes and associations of hyperpituitarism
Usually due to isolated pituitary tumour
May also be ectopic in origin
Can be often associated with visual field and other (e.g. cranial nerve) defects and endocrine-related signs and symptoms
Why do pituitary tumours often cause visual field defects
At the optic chiasm, fibres from the nasal retinae cross
Light from the outer aspects of the visual fields strikes the nasal aspect
Compression of the crossing fibres at the optic chiasm causes a loss of vision from the outer temporal visual fields
(bitemporal hemianopia)
What can hyperpituitarism result in (adenohypophysis-hypophysis)
ACTH -> Cushings TSH -> thyrotoxicosis Gonadotrophins -> precocious puberty in children Prolactin -> Hyperprolactinaemia GH -> Gigantism, acromegaly
What are the physiological and pathological causes of hyperprolactinaemia
Physiological - pregnancy, breastfeeding
Pathological - Prolactinoma (often micro adenomas <10mm)
What is the most common functioning pituitary tumour
Prolactinoma
How does prolactin affect GnRH
high prolactin suppresses GnRH pulsality
What are the symptoms of hyperprolactinaemia due to pituitary adenoma in women
Galactorrhoea (milk production)
Secondary amenorrhoea (or oligomenorrhoea)
Loss of libido
Infertility
What are the symptoms of hyperprolactinaemia due to pituitary adenoma in men
Galactorrhoea uncommon
Loss of libido
Erectile dysfunction
Infertility
How is prolactin secretion regulated
Dopamine from the hypothalamus binds to the D2 receptors on the lactotrophs and prevent prolactin secretion
How is a hyperprolactinaemia treated
Dopamine receptor (D2) agonists that decrease prolactin secretion and reduce tumour size
e.g. bromocriptine, cabergoline
Oral administration
What are the side effects of dopamine receptor agonists
Nausea and vomiting Postural hypotension Dyskinesias Depression Impulse control disorder (pathological gambling, hyper sexuality)
What are the effects of excess GH in childhood and adulthood
child - gigantism
adult - acromegaly
Usually due to benign growth hormone secreting pituitary adenoma
Describe acromegaly
Signs and symptoms progress gradually Untreated it is associated with increased morbidity and mortality Cardiovascular disease - 60% Respiratory complications - 25% Cancer - 15%
What grows in acromegaly
Periosteal bone Cartilage Fibrous tissue Connective tissue Internal organs (cardiomegaly, splenomegaly, hepatomegaly, etc.)
What are the clinical features of acromegaly
Excessive sweating (hyperhidrosis)
Headache
Enlargement of supraorbital ridges, nose, hands and feet , thickening of lips
Enlarged tongue (macroglossia)
Mandible grows -> jaw protusion (prognathism)
Carpal tunnel syndrome (median nerve compression)
Barrel chest, kyphosis
What are the metabolic effects of acromegaly
- Increased endogenous glucose production, decreased muscle glucose uptake
- Increased insulin production -> insulin resistance
- Impaired glucose tolerance
- Diabetes mellitus
What are the complication of acromegaly
Obstructive sleep apnoea
Hypertension
Cardiomyopathy
Increased risk of cancer
Describe the co-secretion of prolactin and GH in acromegaly
Prolactin is often high in acromegaly
Hyperprolactinaemia will cause secondary hypogonadism
How is acromegaly diagnosed
Elevated serum IGF-1
Failed suppression of GH following oral glucose load (oral glucose tolerance)
(GH is pulsatile - unhelpful)
Describe what happens when oral glucose is given for diagnosis acromegaly
Increase in GH in response to glucose (no explanation, just used for diagnosis), which then returns to normal after 2 hours
Those who are normal will see a decrease in GH and then increases after 2 hours, then decreasing after 2.5 hours
What is the treatment of acromegaly
Surgery (trans-sphenoidal)
Somatostatin analogues e.g. octreotide
Dopamine agonists e.g. cabergoline
Radiotherapy
Describe somatostatin analogues
Injection (short acting) or monthly depot
Reduces GH secretion and tumour size
Pre-treatment before surgery may make it easier
Use post-operatively if not cured or whilst waiting for radiotherapy to take effect
What are the side effects of somatostatin analogues
Nausea
Diarrhoea
Gallstones
