Pituitary Gland Conditions

a) Posterior pituitary gland

• Diabetes insipidus (DI) – Production of much dilute urine (>3L/day) due to poor water reabsorption.

i) Central DI – This is a failure of the pituitary gland to produce ADH

Causes: Idiopathic (50%), congenital defect in ADH gene DIDMOAD + trauma/tumour

ii) Nephrogenic DI – This is an impaired renal response to ADH

Causes: Inherited genes, low K⁺, high Ca²⁺, Drugs (e.g. lithium, demeclocycline)

iii) Dipsogenic DI – This is producing large amounts of urine due to drinking too much water

Symptoms – These resemble those of losing water giving hypernatremia

– Polyuria + polydipsia (e.g. kids drinking bathwater) with risk of life-threatening dehydration

– Dilute urine and low specific gravity –> a high urine osmolality (> 700mOsm/kg) excludes DI

Diagnosis – ­ Increased Plasma Osmolality, Decreased Urine Osmolality

– Water deprivation test –> this tests ability of the kidney to concentrate urine

–> Patient empties bladder and is then deprived of water for 8 hours

–> Weighed hourly and urine collected every 2h – measure volume and osmolarity

–> After 8h, if urine osmolarity <600mOsmol/kg (dilute), give desmopressin

–> If osmolarity does not increase after 4h, then nephrogenic, otherwise neurogenic

Treatment – Central DI –> Desmopressin

– Nephrogenic DI –> Treat the cause + Bendroflumethiazide diuretic – acts as an anti-diuretic

• SIADH syndrome – This is a disease which leads to excessive ADH secretion

Causes: Often due to ectopic ADH production (e.g. small cell lung carcinoma)

– CNS trauma + Drugs (SSRIs, opiates, TCAs)

Symptoms – Hyponatremia (low serum Na⁺ and low osmolarity) and low volume urine

– This leads to neuronal swelling and cerebral oedema giving rise to seizures, headache

Diagnosis – Concentrated urine Na⁺ > 20mM, and >100mOsmol/kg with hyponatraemia (Na⁺<125mM)

Management – Water restriction

– Demeclocycline – an antibiotic which also reduces the sensitivity of the collecting duct to ADH

– ADH receptor antagonists – Vaptan drug family

b) Anterior pituitary gland

• Hypopituitarism – This is decreased secretion of anterior pituitary hormones.

– Most commonly affected hormone is GH –> FSH/LH –> TSH –> ACTH –> Prolactin

Causes – These occur at 3 levels

– Hypothalamus – Kallman’s syndrome, tumour

– Pituitary stalk – Trauma, Carotid artery aneurysm

– Pituitary gland – Adenoma + apoplexy (bleeding of adenoma, haemorrhage of gland)

• Sheehan syndrome – during pregnancy, the gland doubles in size but blood supply hardly increases

– Blood loss during parturition gives ischaemia and infarction of pituitary gland

– Patients get fatigued + have poor lactation

• Empty Sella syndrome – arachnoid mater and CSF herniate into Sella compressing the pituitary

• Kallman Syndrome – failure of development of GnRH neurons derived from olfactory epithelium

– Gives anosmia (lack of smell) + cleft lip + colour blindness

– Low LH/FSH and low sex hormones cause delayed puberty and hypogonadism

– Height is usually normal or above average

Symptoms:  Hypopituitarism gives many symptoms due to the effect on the corresponding hormones.

Tests: Different tests are carried out to work out which hormones are affected e.g. LH/FSH, IGF-1

Treatment – Hormone replacement therapy

• Pituitary adenoma – This is a benign tumour of the anterior pituitary cells.

– It can be a microadenoma (<1cm) or macro (>1cm)

– Can also be functional (hormone-producing) or non-functional (silent)

– Most common tumour is prolactin secreting –> non-functional –> GH secreting –> ACTH secreting

i) Non-functional tumours – these often present with mass effect due to structural compression

– Can cause bitemporal hemianopia –> compression of the optic chiasm

– Visual disturbances –> pressure on cavernous sinus pressing CN III, IV and VI

– Can cause hypopituitarism –> compression of normal pituitary tissue

– Early morning headaches, worse when lying down

ii) Functional tumours – these present with the features based on the type of hormone produced

– Usually prolactin, GH and ACTH producing – the others are very rare

Tests – Pituitary blood profile (GH, prolactin, ACTH, FH, LH and TFTs)

– MRI provides visualization of pituitary gland enlargement

– Formal visual field testing

Management – if it affects hormones, treat accordingly

– Surgery – transphenoidal hypophysectomy or radiotherapy (residual/recurrent adenomas)

Symptoms: (Children) Gives growth failure, and compression of structures

– Bitemporal hemianopia (lower quadrants worse)

(Adults) Amenorrhoea, loss of libido, DI, hyperphagia

Imaging – CT/MRI shows calcifications (as if derived from “tooth like tissue”)

Management – Surgical removal, but usually recurs after resection

• Hyperprolactinemia – This is the most common hormone disturbance on the pituitary

Causes: Most often due to a pituitary adenoma increasing production

– Also due to reduced inhibition e.g. dopamine antagonists (Haloperidol, Domperidone)

– Pregnancy and raised oestrogen           – Polycystic Ovary syndrome

– Acromegaly (1/3 of patients)

– Primary hypothyroidism –> as TRH stimulates prolactin release

Symptoms: As well as direct effects on lactation, raised prolactin inhibits GnRH which decreases testosterone and estrogen giving secondary effects like osteoporosis.

Diagnosis – MRI visualisation of pituitary gland

Management – 1st choice is dopamine agonists to reduce secretion e.g. Bromocriptine/Cabergoline

– 2nd line is surgery

• Acromegaly

– This is a condition caused by increased secretion of growth hormone from the pituitary

– Most often due to a pituitary adenoma

Symptoms: GH stimulates bone and soft tissue growth through IGF-1

– (Children) – gigantism due to increased bone growth

– (Adults) – enlarged hands, tongue, jaw and feet (increase shoes size)

    – Acroparathesia – tingling in the extremities

    – Pituitary tumour features (headache + hyperprolactinaemia)

    – Excessive sweating and oily skin, due to sweat gland hypertrophy

Complications – Growth of visceral organs leads to cardiomyopathy

– Hypertension

– Secondary diabetes mellitus as GH induces gluconeogenesis                

– Colorectal cancer

Diagnosis:

– 1st line is to check if Serum IGF-1 level is raised

– Confirmation test is Oral glucose tolerance test –> Normally GH supressed to <2mu/L with glucose

– In acromegaly there is no suppression of GH

– MRI pituitary fossa to visualise tumour

Management:

– 1st line is transphenoidal surgery

– Octreotide – somatostatin analogue, used as adjunct to surgery

– Pegvisomant – GH receptor antagonist, given by subcutaneous injection

– Can use radiotherapy in older patients of if the methods above fail