The document discusses screening tests for Cushing's syndrome, including the low-dose dexamethone suppression test and urinary free cortisol tests. The low-dose dexamethone suppression test involves administering 1mg of dexamethone and measuring cortisol levels the next morning, which should be below 50 nmol/L. However, some drugs and medical conditions can result in false positives on this test. Urinary free cortisol measured over 24 hours can also help screen for Cushing's syndrome, though assay methods are cumbersome and values may be elevated in stressed patients as well. Both tests are part of the screening process to evaluate for hypercortisolism.
5. Control of Pituitary
Hormone Secretion
Hypothalamic/pituitary/end organ axis
Points to note
- CNS inputs
- pulsatile secretion
- negative feedback
- diurnal/monthly rhythms
- stress
- drugs
6. Hormone Structure
HYPOTHALAMIC
Hormone Amino acids Notes
GnRH 10 High potency
Analogues available
TRH 3 Use in TRH test
GHRH 44 Analogues available
CRH 41 Use in CRH test
GHRIH 14 + 28
(Somatostatin)
Dopamine = Dihydroxyphenyl-ethylamine (Catecholamine)
13. Intrapituitary cytokines
• The net secretion of pituitary hormones is determined from
signals from
– Hypothalamus
– Intrapituitary factors
– Feedback mechanisms
• Intrapituitary control by cytokines is an important control
mechanism for pituitary hormone secretion
• Several of these cytokines signal through a common
receptor subunit (GP 130) linked to the Janus kinase signal
transduction activation transcription cascade (JAK-STAT)
• ACTH and GH are induced by cytokines in this group
including IL6 and leukaemia inhibitory factor
14. Presentation of Pituitary Tumours
Space-occupying effects
• Headache
• Visual field defects
• Disorders of eye movement
Syndromes of pituitary hormone hypersecretion
• Prolactinoma
• Acromegaly
• Cushings Disease
• TSH, LH, FSH secreting adenomas
Hypopituitarism
Pituitary apoplexy
Incidental finding
16. Investigation of
Pituitary Tumours
• CT/MRI scan
• Visual fields
• Endocrine
Treatment
• Medical therapy
– Bromocriptine
– Somatostatin analogues
– Metyrapone
• Surgery
• Radiotherapy
17. Hypopituitarism
total selective
Causes
Infection
Infarction
Cysts, Tumours, Pituitary surgery or irradiation
Head injury
LH/FSH ↓ - Fertility (hypogonadism)
GH ↓ - ↓ Growth in children
Non specific effects in adults
ACTH ↓ - Adrenal dysfunction
TSH ↓ - Hypothyroidism
Treatment by oral replacement of steroid or thyroid hormones
GH injections
19. Measurement of anterior
pituitary hormones
1. Baseline measurements
ACTH (Cortisol 9am, 12mn), TSH (T4), Prolactin, LH/FSH
(Testosterone, Oestradiol)
2. Dynamic function tests
Why?
- low pituitary hormone levels not diagnostic
- normal levels do not exclude pituitary disease
- pulsatile excretion + diurnal variation confuse interpretation of
baseline levels
- if baseline levels are high dynamic tests can aid in differential
diagnosis
Hypofunction → stimulation tests
Hyperfunction → suppression tests
20. Measurement factors
1. Patient - pulsitility
- diurnal/(monthly) variation
- stress, drugs etc.
2. Samples - serum/plasma
- storage at 4°C for 2-3 days and
-20°C for extended periods
ACTH → -70°C
3. Assay - competitive immunoassay
- 2 site immunometric assay
- bioassay - in vitro, in vivo
4. Ref. ranges - units (IU/l for most pituitary hormones)
- age, sex, time of day, time of month,
etc
23. Thyroid
• Largest Endocrine organ in the body
• Involved in production, storage, and release
of thyroid hormone
• Function influenced by
– Central axis (TRH)
– Pituitary function (TSH)
– Comorbid diseases (Cirrhosis, Graves, etc.)
– Environmental factors (iodine intake)
24. Thyroid (cont)
• Regulates basal metabolic rate
• Improves cardiac contractility
• Increases the gain of catecholamines
• Increases bowel motility
• Increases speed of muscle contraction
• Decreases cholesterol (LDL)
• Required for proper fetal neural growth
25. Secretion of Thyroid Hormone
• Stimulated by TSH
• Endocytosis of colloid on apical membrane
• Coupling of MIT & DIT residues
– Catalyzed by TPO
– MIT + DIT = T3
– DIT + DIT = T4
• Hydrolysis of Thyroglobulin
• Release of T3, T4
• Release inhibited by Lithium
27. Thyroid Hormone
– Majority of circulating hormone is T4
• 98.5% T4
• 1.5% T3
– Total Hormone load is influenced by serum binding
proteins (TBP, Albumin, ??)
• Thyroid Binding Globulin 70%
• Albumin 15%
• Transthyretin 10%
– Regulation is based on the free component of thyroid
hormone
28. Hormone Binding Factors
• Increased TBG
– High estrogen states (pregnancy, OCP, HRT, Tamoxifen)
– Liver disease (early)
• Decreased TBG
– Androgens or anabolic steroids
– Liver disease (late)
• Binding Site Competition
– NSAID’s
– Furosemide IV
– Anticonvulsants (Phenytoin, Carbamazepine)
31. Hypothyroid
• Symptoms – fatigability, coldness, weight gain,
constipation, low voice
• Signs – Cool skin, dry skin, swelling of face/hands/legs,
slow reflexes, myxedema
• Newborn – Retardation, short stature, swelling of
face/hands, possible deafness
• Types of Hypothyroidism
– Primary – Thyroid gland failure
– Secondary – Pituitary failure
– Tertiary – Hypothalamic failure
– Peripheral resistance
32. Hypothyroid
• Cause is determined by
geography
• Diagnosis
– Low FT4, High TSH (Primary,
check for antibodies)
– Low FT4, Low TSH (Secondary or
Tertiary, TRH stimulation test,
MRI)
• Treatment
– Levothyroxine (T4) due to longer half life
– Treatment prevents bone loss, cardiomyopathy, myxedema
33. Hashimoto’s
(Chronic, Lymphocytic)
• Most common cause of hypothyroidism
• Result of antibodies to TPO, TBG
• Commonly presents in females 30-50 yrs.
• Usually non-tender and asymptomatic
• Lab values
– High TSH
– Low T4
– Anti-TPO Ab
– Anti-TBG Ab
• Treat with Levothyroxine
34. Goiter
• Endemic goiter
– Caused by dietary deficiency of Iodide
– Increased TSH stimulates gland growth
– Also results in cretinism
• Goiter in developed countries
– Hashimoto’s thryoiditis
– Subacute thyroiditis
• Other causes
– Excess Iodide (Amiodarone, Kelp, Lithium)
– Adenoma, Malignancy
– Genetic / Familial hormone synthesis defects
38. Graves
• Most common cause of hyperthyroidism
• Result of anti-TSH receptor antibodies
• Diagnosis
– Symptoms of hyperthyroidism
– Clinical exopthalmos and goiter
– Low TSH, normal/high FT4, TSI (Optional)
• If no clinical findings I123
may demonstrate increased
uptake.
• Treatments
– Medical – Propothyouracil, Methimazole, Propranolol
– Surgical – Subtotal Thyroidectomy
– Radiation – RAI ablation [I131
(µCi/g) x weight / %RAIU]
39.
40.
41. Subacute Thyroiditis
(DeQuervain’s, Granulomatous)
• Acute viral infection of thyroid gland
• Presents with viral prodrome, thyroid tenderness, and
hyperthyroid symptoms
• Lab values
– Variable TSH, T4
– High ESR
– No antibodies
• Treatment
– APAP, NSAID
– Prednisone (?)
– Levothyroxine (?)
43. Euthyroid Sick
• Results from inactivation of 5’-Deiodinase, resulting
in conversion of FT4 to rT3.
• Generally occurs in critically ill patients, but may
occur with DM, malnutrition, iodine loads, or
medications (Amiodarone, PTU, glucocorticoids)
• Treatment
– Avoid above medications
– Treat primary illness
– T3, T4 not helpful
44. Thyroid Storm
• Causes
– Surgery
– Radioactive Iodine Therapy
– Severe Illness
• Diagnosis
– Clinical – tachycardia, hyperpyrexia, thyrotoxicosis symptoms
– Labs (Low TSH, High T4, FT4)
• Treatment
– Propranolol IV vs. Verapamil IV
– Propylthiouracil, Methimazole
– Sodium Iodide
– Acetamenophen, cooling blankets
– Plasmapheresis (rare)
– Surgical (rare)
45. Adrenal Disease
• Clinical manifestations result from:-
– Overproduction or deficiency of: -
• Glucocorticoids
• Mineralocorticoids
• Androgens
• Hyper-secretion may present differently
depending on the disease mechanism.
• Hypo-secretion may only be apparent at
times of stress.
46. Adrenal Disease
• Causes of dysfunction: -
– Hyper-secretion:-
• Primary adrenal pathology:-
– Adenoma
– Hyperplasia
– Carcinoma
– Enzyme defects
• Secondary: -
– Increased/autonomous ACTH production
– Pathology of the Renin/angiotensin system
– Receptor defects
– Enzyme defects.
48. Adrenal Disease
• General Concept for Investigations: -
• Establish Hyper - or Hypo-function: -
– Use screening tests:-
• Short synacthen, dexamethasone suppression
• Differentiate the cause of the dysfunction: -
– Use secondary tests:-
• ACTH measurement , long synacthen, high dose
dexamethasone.
49. Investigation of Adrenal Disease
• Requires knowledge of: -
– Biological rhythms
– Concept of feedback controls
• Limitations of analytical techniques.
50. Glucocorticoid Excess
• Cushing’s syndrome:-
– Features of glucocorticoid excess.
– Low ACTH.
– High ACTH: ectopic or exogenous.
• Cushing’s disease: -
– Glucocorticoid excess
– High ACTH: -
• Pituitary origin as described by Cushing.
• Pseudo-Cushing’s disease: -
– Alcohol = functional 11β-OH steroid
dehydrogenase deficiency?
54. Screening for Cushing’s Syndrome
• Low dose dexamethasone suppression test.
Ann Clin Biochem 1997;34:222-229.
– Procedure: -
• 1mg dexamethasone 23.00-24.00h
• Serum cortisol 09.00h following day.
• Cortisol should = < 50 nmol/L
– Interpretation: -
• Cortisol should = < 50 nmol/L (not everyone agrees
with this)
• 2% False negatives
55. Screening for Cushings Syndrome
• Low dose dexamethasone suppression test.
– Drug effects = false positive:-
• Oestrogen & tamoxifen due to effect on Cortisol
Binding Globulin.
• Nasal decongestants and oral contraceptives
– Obesity = no effect
– Weight reduction = false positives in 25%
– Alcohol = false positives
– Depressive illness = 30 - 50% false positives
56. Screening for Cushing's Syndrome
• Urinary Free Cortisol: -
– 24 hour collection to give an integrated result.
– Reference values vary with assay:-
• Males <300 nmol/24 hours
• Females <210
– Elevated in 95% of Cushing’s and in stressed subjects
(False +ve)
– Assays are cumbersome, often involving extraction's.
– Use as part of screening process for in-patients.
57. Screening for Cushing's Syndrome
• Diurnal variation: -
– Serum Cortisol at Midnight and 09.00h.
• Avoid stress.
– Normal:-
• 08.00h - 10.00h 130-690 nmol/L
• 22.00h - 24.00h <260 nmol/L
or 50% of 09.00h value
Check local reference values
– Cushings:-
• Loss of diurnal variation.
58. Differential Diagnosis of Cushing’s
Syndrome
• Primary Adrenal disease? Non-ACTH
dependant.
– ACTH measurement = low.
– High dose dexamethasone suppression test.
– Measurement of androgens (DHEAS).
• Secondary Disease? ACTH dependant.
– ACTH measurement = high or inappropriate
59. Differential Diagnosis of Cushing’s
Syndrome
• High dose dexamethasone: -
– Helps differentiate between pituitary and
ectopic ACTH production.
– 2mg 6h for 2 days: -
• measure Cortisol & ACTH 09.00h day 1
• Give Dexamethasone 6 hourly from 09.00h day 1
• measure cortisol and ACTH 09.00h day 3.
60. Differential Diagnosis of Cushing’s
Syndrome
• High dose dexamethasone Cont.: -
– Cushing’s disease (pituitary adenoma):-
• serum cortisol suppresses to 50% of basal.
• ACTH in basal sample elevated or high normal and
suppresses.
– Ectopic ACTH:-
• ACTH may be very high >200 ng/L
• Cortisol fails to suppress
– Adrenal Carcinoma or adenoma: -
• Cortisol does not suppress & ACTH low.
62. Adrenal Failure
• Epidemiology:
– Prevalence 5/100,000
• Sex:
– Autoimmune Addison’s more common in women
• Genetics
– May be a family history of autoimmune
Addisons
• Geography
– Local prevalence of TB leading to adrenal failure
66. Adrenal Failure.
Endocrine Investigation .
• Test adrenal reserve.
• Random and “normal” 09.00h serum
cortisol may be misleading.
• Urine cortisol assay has no place in the
diagnosis of adrenal failure
67. Investigation Adrenal Failure.
Endocrine Investigation.
• Establish whether patient is receiving
steroid replacement.
– Prednisone/prednisilone cross-react in assays
for cortisol.
– Hydrocortisone = Cortisol.
68. Adrenal Failure.
Endocrine Investigation .
• Establish Deficiency: -
– Short Synacthen test:-
– Can be performed at any time of day.
– Non-stressed patient
– 250 µg tetracosactrin i.m. (Check local policies for
surface area corrections etc).
– Blood for cortisol at 0, 30, and 60 mins.
– Plasma for ACTH at time 0.
• Interpretation:-
– Serum cortisol should rise by 250 nmol/L to a
concentration >550 nmol/L
69. Adrenal Failure.
Endocrine Investigation .
• Primary or Secondary Failure: -
– Patient history
– Previous steroid therapy.
– ACTH: -
– Primary = High
– Secondary = Low
• High dose synacthen: -
– 1 mg i.m.
– Cortisol 0, 30, 60, 300 mins.
– Cortisol at 300 mins = >900 nmol/L
– Deficient rise = secondary failure.
– Pituitary function tests required.
70. Mineralocorticoid Excess.
• Primary hyperaldosteronism :-
– Overproduction of aldosterone independent of it’s
normal chronic regulator Angiotensin 2 :-
• Adenoma: Surgical Treatment
– Aldosterone
– Plasma Renin
– High Aldosterone/Plasma Renin Ratio
• Bilateral Adrenal cortical Hyperplasia.
• Sporadic or Familial hyperaldosteronism (Type FH2).
• ACTH dependant release. (dexamethasone suppressible
FH1).
72. Mineralocorticoid Excess.
When to Investigate?
• Hypertension: -
– Long-standing & resistant to drugs
• Hypokalaemia and alkalosis:-
• Unprovoked by: -
Diuretics, vomiting or diarrhoea
• Profound provoked hypokalaemia
(Gordon Lancet 1994;344:240-243. 50% of Patients are
Normokalaemic but with abnormal Aldo/PRA ratios).
73. Mineralocorticoid Excess.
When to Investigate?
• Inappropriate loss of urine potassium in the
presence of K+ deficit (Urine [K+] >30 mmol/L).
• Hypertension with a family history of 10
hyperaldosteronism.
• Polyuria, muscle weakness, tetany, polyuria.
74. Mineralocorticoid Excess.
Biochemical diagnosis.
• Plasma aldosterone, Plasma Renin Activity (PRA) and
K+
from a supine patient. Calculate ratio.
• Assess renal function.
• K+
deficits should be corrected with plasma K+
>4.00mmol/L.
• Modulates aldosterone output.
• Reduce high dose β-blockers.
• Lowers renin more than Aldosterone.
77. CASE 4A
A 47 year old smoker with a history of asbestos exposure presented with a 6 month history of
lethargy, headache, weight loss and erectile impotence. The following blood results were obtained
on admission:
Cortisol 65 nmol/l
Growth hormone 1.9 mU/l
FT4 8 pmol/l
TSH 1.1 mU/l
LH < 1.0 IU/l
FSH 1.9 IU/l
Testosterone 1.0 nmol/l
Prolactin 360 mU/l
Questions
1. Explain the patient's symptoms in light of these results.
2. What is the differential diagnosis at this stage?
3. What further blood/urine tests would you like to carry out?
78. CASE 4
1. The patients symptoms are lethargy, headache, weight loss and erectile impotence.
The lethargy could be explained by the low levels of T4 and cortisol. A deficiency of
cortisol can lead to loss of fluid and therefore weight loss. The headache could be due
to the presence of a pituitary tumour and the erectile impotence due to the low
testosterone level.
2. The levels of cortisol, T4 and testosterone are low coupled with normal/low levels
of TSH and LH/FSH and a normal serum prolactin. A likely diagnosis is that the
patient has hypopituitarism. This can be due to the presence of a pituitary tumour
(non secreting) damage to the pituitary by infection, infarction, tuberculosis etc. Other
possible diagnoses include hypothalamic disease , general illness or the presence of low
levels of hormone binding proteins.
3. Further baseline hormone tests would include the measurement of sex hormone
binding globulin (SHBG). A baseline ACTH measurement may be useful to
distinguish primary from secondary adrenal failure. Due to the overlap between the
baseline levels of pituitary hormones in normals and patients with hypopituitarism it
would be appropriate to perform dynamic function tests of pituitary function. Tests
commonly performed include the Insulin Tolerance Test, LHRH test and TRH test.
Measurements of plasma urea and electrolytes and blood sugar would also be
appropriate in this patient as these are frequently abnormal in patients with
hypopituitarism due to low cortisol and growth hormone levels.
79. CASE 4B
Following removal of a cystic mass from the pituitary, combined pituitary function tests using insulin, GnRH
and TRH i.v. were carried out and the results were as follows:
Glu Co GH TSH LH FSH FT4 Testo Prolactin
0 4.4 580 < 1.0 1.7 2.3 4.8 20 3.5 230
20 5.8
30 1.2 280 < 1.0 6.5 5.9
60 2.8 725 3.4 4.5 7.3 7.3
90 3.1 895 2.1
120 3.3 550 1.3
Questions (cont)
4. What patient preparation is necessary before performing this test and why?
5. What is the importance of the serum glucose level during the test.
6. Interpret the response of each hormone to stimulation and suggest what medical treatment this
patient might now require.
80. CASE 4 cont.
4. Prior to the performance of a combined pituitary function test the patient should be resting and
under no stress. An indwelling needle should be inserted 30 minutes before the test commences.
The test should be carried out under medical supervision and glucose must be available at all
times.
5. The serum glucose must fall into the hypoglycaemic range (< 2.5 mmol/l) at some stage during
the test. In addition the patient should show symptoms of hypoglycaemia.
6. The high baseline cortisol is probably due to the patient being stressed at the start of the test.
Adequate hypoglycaemia has been achieved and the patient has shown a normal cortisol response
to this. The TSH response to TRH is normal. The patient has a borderline response of LH and
FSH to GnRH stimulation and a subnormal growth hormone response to hypoglycaemia. The
testosterone level is still suppressed.
The patient will probably require testosterone replacement therapy. The role of growth hormone
replacement therapy in adults is still being investigated.
81. CASE 5
After stopping a combined oral contraceptive pill a 25 year old local health authority worker
presented with an eight month history of amenorrhoea which failed to respond to the oestrogen
antagonist clomiphene. She was referred to the endocrine clinic with serum prolactin
4615 mU/l. The diagnosis of a prolactinoma was supported by the findings of an 11mm diameter
tumour in the pituitary gland on CT scan, which was initially treated with bromocriptine, followed
by trans-sphenoidal adenomectomy. The results of the combined pituitary function tests were as
follows:
Pre-operatively:
Glu Co GH TSH LH FSH T4 Prolactin E2 Prog
0 3.9 540 1.1 2.3 3.4 3.4 96 1190 120 < 2
20 12
30 1.2 410 2.6 19 9.6
60 1.7 670 14 13 16 9.3
90 2.1 770 28
120 2.6 840 25
Post-operatively:
Glu Co GH TSH LH FSH T4 Prolactin E2 Prog
0 3.9 330 0.8 2.0 4.7 < 1.0 149 < 80 2960 > 92
20 11
30 1.1 355 11 4.8 < 1.0
60 0.8 535 26 5.6 5.1 < 1.0
90 1.7 560 37
120 4.2 580 43
Questions
1. Was adequate hypoglycaemia achieved?
2. Do you think the patient's surgery was successful?
3. Do you think that pituitary function was preserved post-operatively?
82. CASE 5
1. Yes, the serum glucose has fallen to 1.2 mmol/l which is well within the
hypoglycaemic range.
2. Yes, the serum prolactin has fallen to less than 80 mu/l post operatively and the
luteal phase oestradiol and progesterone levels imply that the patient is now ovulating.
Note the response of the serum prolactin to bromocryptine therapy prior to surgery. In
prolactin secreting pituitary tumours it is recommended that a trial of drug treatment
should be given prior to surgery.
3. The post operative combined pituitary function test results imply that pituitary
function has been preserved. The poor LH/FSH response to GnRH is probably due to
the tests having been performed in the luteal phase of the cycle.
83. CASE 6
A 33 year old warehouseman presented to his GP with a 3 year history of weight gain, increasing
thirst and polyuria. Initial investigations revealed:
Na 145 mmol/l Osmolality serum 302 mosmol/kg
K 4.3 mmol/l urine 80 mosmol/kg
Urea 2.1 mmol/l
Potassium 4.4 mmol/l
Fasting glucose 4.5 mmol/l
Following his admission, the results of the combined pituitary function tests were as follows:
Glu Co GH TSH LH FSH FT4 Prolactin Testo
0 4.5 510 < 0.5 1.0 < 1.0 < 1.0 9 1180 1.6
20 2.5 5.1
30 2.3 350 0.5 < 1.0 < 1.0
60 2.6 355 0.6 5.9 < 1.0 < 1.0
90 3.7 465 0.6
120 4.3 310 0.8
Questions
1. What is the likely site of the pathology in this patient?
2. Can you explain the raised serum prolactin in this patient?
3. What further biochemical investigation would you recommend and what would you
expect to find?
84. CASE 6
1. The patients symptoms and the presence of a high serum osmolality without
concentration of the urine suggests a diagnosis of diabetes insipidus. The patient has a
low basal testosterone and borderline F T4. There does appear to be a lack of growth
hormone response. There is also a lack of response of LH/FSH in the GnRH test. The
combination of apparent A.D.H. deficiency and pituitary dysfunction suggest that the
most likely site of pathology in this patient is the hypothalamus.
2. Prolactin secretion is under inhibitory control by dopamine produced in the
hypothalamus. Disorders of the hypothalamus may inhibit dopamine secretion and
therefore cause an increase in serum prolactin.
3. The most helpful further investigation would be a water deprivation test. If the
patient has cranial diabetes insipidus the urine will fail to concentrate after 8 hours fluid
restriction but will concentrate when the patient is given desmopressin.
