Hypopituitarism Flashcards
Hypopituitarism
Hypopituitarism
Adult growth hormone deficiency
low peak growth hormone levels in response to insulin-induced hypoglycaemia
Features - mix
low ACTH: tiredness, postural hypotension
low gonadotrophins: amenorrhoea
low TSH: constipated
Hypopituitarism - Example Question
A 40 year old man presents to the Emergency Department with tiredness and dizziness (worse on standing) which has been ongoing for the past few months. He had a past medical history of epilepsy and mentions that he has had ‘brain surgery’ in the past. He is on some medications but cannot remember the names. He has no allergies.
On assessment, he has no focal neurological deficit and cardiovascular/respiratory examination is normal. Observations show a blood pressure of 135/90 mmHg (dropping to 105/82 mmHg on standing), a heart rate of 67 beats per minute, a temperature of 36.2 degrees, oxygen saturations of 94% on air and a respiratory rate of 18/min. Given his medical history, you opt to keep this gentleman in the short stay unit for observation overnight.
Baseline blood tests are as follows:
Hb 125 g/l WCC 9.2 x109/l Plt 290 x109/l CRP 10 mg/l Gluc 3.9 mmol/l Na+ 138 mmol/l K+ 5.8 mmol/l Ur 7.2 mmol/l Cr 100 µmol/l TSH 0.4 mU/l T4 5.0 pmol/l
Given the above, what is the most likely underlying diagnosis?
> Hypopituitarism Hypothyroidism Acromegaly Pheochromocytoma Medication side effects
This gentleman has hypopituitarism following ‘brain surgery’. Though the details of this are obscured in the question, it is likely that removal of a pituitary mass with trans-sphenoidal surgery. This is exhibited by fairly non-descript symptoms coupled with some underlying evidence of lack of anterior pituitary hormones: low BP/dizziness/postural hypotension, high/normal K+, low/normal Na+ and low/normal blood glucose all indicate lack of cortisol due to low ACTH; the low/normal temperature and heart rate and the tiredness steer you towards low thyroxine level due to lack of TSH.
This gentleman needs assessment of his pituitary function. This can be done in many ways. A baseline pituitary hormone profile can be quite useful; however the most definitive tests involve assessing dynamic pituitary function. The insulin stress test (coupled with TRH and GnRH tests) creates a hypoglycaemic effect in the body and the response of the pituitary (cortisol surge) is measured. However, inducing hypoglycaemia in epileptics, such as this gentleman, is contraindicated. Therefore the next best investigation is the glucagon stimulation test which mimics hypoglycaemia in the body and causes a fake stress on the pituitary, therefore being safe to use in epileptics.
Dynamic Pituitary Function Tests
Hormones assessed = TSH, LH, FSH, GH, Cortisol, Serum glucose
Used to assess patients with suspected primary pituitary dysfunction
Insulin, TRH (thyrotrophin releasing hormone) and LHRH (luteinizing hormone releasing hormone) are given to the patient following which, the serum glucose, cortisol, growth hormone, TSH, LH and FSH levels are recorded at regular intervals (prolactin levels are sometimes measured)
A NORMAL dynamic pituitary test has the following:
- GH level rises >20mu/L
- Cortisol level rises >550mmol/L
- TSH level rises >2mu/L from baseline
- LH and FSH should double
NB: A dopamine antagonist test using metoclopramide may also be used in Ix of hyperprolactinaemia. A normal response is a 2-fold rise in prolactin. A blunted prolactin response suggests a PROLACTINOMA
Insulin Stress Test
= Ix for Hypopituitarism
Basics:
- Used in Ix of hypopituitarism
- IV insulin given, GH and cortisol levels measured
- With normal pituitary function GH and Cortisol should rise
NB Insulin stress tests are also occasionally used to differentiate Cushings from pseudo-cushings (Cushings = insulin resistance)
Contraindications:
- Epilepsy
- Ischaemic heart disease
- Adrenal insufficiency
With normal pituitary function, if IV insulin is given, GH and Cortisol should RISE
With reduced pituitary function, IV insulin given, GH and Cortisol will NOT rise/will not rise sufficiently
