Endocrine tests and concepts Flashcards
Most common cause of hypothyroidism?
Hashimoto’s thyroiditis
Other causes of hypothyroidism?
Subacute thyroiditis (de Quervain’s)
associated with a painful goitre and raised ESR
Riedel thyroiditis
fibrous tissue replacing the normal thyroid parenchyma
causes a painless goitre
Postpartum thyroiditis
Drugs
lithium
amiodarone
Iodine deficiency
the most common cause of hypothyroidism in the developing world
Most common cause of thyrotoxicosis?
Graves disease
Other causes of thyrotoxicosis?
toxic multinodular goitre
Amiodarone
Antibodies in thyroid disease
Anti-thyroid peroxidase (anti-TPO) antibodies
TSH receptor antibodies
Thyroglobulin antibodies
Most common antibody test positive in Graves disease
TSH receptor antibodies are present in around 90-100%
Most common antibody test positive in Hashimoto’s thyroiditis
anti-TPO antibodies are seen in around 90% of patients
What is the TSH / T3/T4 in HYPOthyroidism?
T3/T4 Low
TSH HIgh
What is the TSH / T3/T4 in HYPERthyroidism?
TSH low
T3/T4 HIGH
What is the TSH / T3/T4 in subclinical hypeothyroidism?
TSH raised but T3, T4 normal
What is the TSH/T3/T4 in Secondary hypothyroidism
Both LOW
What is the TSH/T3/T4 in Sick euthyroid syndrome
Both LOW
Poor compliance with thyroxine TSH/T3/T4
T4 Normal but TSH HIgh
Treatment of hypothyroidism?
Thyroxine
Initial treatment of hyperthyroidism (Graves)
propanolol
Tx of Graves disease
carbimazole
Radioiodine treatment
CI of radioiodine tx
pregnancy
age <16
thyroid eye disease
How does carbimazole work?
blocks thyroid peroxidase from coupling and iodinating the tyrosine residues on thyroglobulin → reducing thyroid hormone production
Side effects of carbimazole?
agranulocytosis
Treatment of thyroid storm?
symptomatic treatment e.g. paracetamol
treatment of underlying precipitating event
beta-blockers: typically IV propranolol
anti-thyroid drugs: e.g. methimazole or propylthiouracil
Lugol’s iodine
dexamethasone - e.g. 4mg IV qds - blocks the conversion of T4 to T3
Causes of Cushings syndrome?
ACTH dependent causes
Cushing’s disease (80%): pituitary tumour secreting ACTH producing adrenal hyperplasia
ectopic ACTH production (5-10%): e.g. small cell lung cancer is the most common causes
ACTH independent causes
iatrogenic: steroids
adrenal adenoma (5-10%)
adrenal carcinoma (rare)
Carney complex: syndrome including cardiac myxoma
micronodular adrenal dysplasia (very rare)
2 most commonly used tests in Cushing’s syndrome?
Overnight dexamethasone suppression test
24 hour urinary free cortisol
Test result if neither ACTH / cortisol suppressed
Ectopic ACTH syndrome
Test result if cushing’s disease (i.e. pituitary adenoma → ACTH secretion)
Both suppressed
Adrenal adenoma acth/cortisol tests
cortisol not suppressed, acth suppressed
Acromegaly cause
In acromegaly there is excess growth hormone secondary to a pituitary adenoma in over 95% of cases. A minority of cases are caused by ectopic GHRH or GH production by tumours e.g. pancreatic.
Features of acromegaly
coarse facial appearance, spade-like hands, increase in shoe size
large tongue, prognathism, interdental spaces
excessive sweating and oily skin: caused by sweat gland hypertrophy
features of pituitary tumour: hypopituitarism, headaches, bitemporal hemianopia
raised prolactin in 1/3 of cases → galactorrhoea
6% of patients have MEN-1
Complications of acromegaly
Complications
hypertension
diabetes (>10%)
cardiomyopathy
colorectal cancer
Tests for ACROMEGALY
Serum IGF-1 levels have now overtaken the oral glucose tolerance test (OGTT) with serial GH measurements as the first-line test. The OGTT test is recommended to confirm the diagnosis if IGF-1 levels are raised.
Acromegaly MX
Trans-sphenoidal surgery
ocreotide (somatostatin analogue)
pegvisomant
GH receptor antagonist - prevents dimerization of the GH receptor
dopamine agonists
for example bromocriptine
Normal fasting glucosse
Less than 6.0
Impaired fasting glucose
< or = to 6.1
Impaired glucose tolerance
impaired glucose tolerance (IGT) is defined as fasting plasma glucose less than 7.0 mmol/l and OGTT 2-hour value greater than or equal to 7.8 mmol/l but less than 11.1 mmol/l
Normal glucose tolerance
<7.8
Diabetes insipidus CAUSES
Diabetes insipidus (DI) is a condition characterised by either a decreased secretion of antidiuretic hormone (ADH) from the pituitary (cranial DI) or an insensitivity to antidiuretic hormone (nephrogenic DI).
Causes of Cranial DI
idiopathic
post head injury
pituitary surgery
craniopharyngiomas
infiltrative
histiocytosis X
sarcoidosis
DIDMOAD is the association of cranial Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy and Deafness (also known as Wolfram’s syndrome)
haemochromatosis
Causes of nephrogenic DI
genetic:
more common form affects the vasopression (ADH) receptor
less common form results from a mutation in the gene that encodes the aquaporin 2 channel
electrolytes
hypercalcaemia
hypokalaemia
lithium
lithium desensitizes the kidney’s ability to respond to ADH in the collecting ducts
demeclocycline
tubulo-interstitial disease: obstruction, sickle-cell, pyelonephritis
Investigations in DI
high plasma osmolality, low urine osmolality
a urine osmolality of >700 mOsm/kg excludes diabetes insipidus
water deprivation test
Where is ADH secreted from
Posterior pituitary gland
What does ADH do?
It promotes water reabsorption in the collecting ducts of the kidneys by the insertion of aquaporin-2 channels.
What would be the water deprivation test result NORMAL
Starting plasma osmolality: LOW
Final urine osmolality: >600
Urine osm. post-DDAVP: >600
What would be the water deprivation test result in psychogenic polydipsia
Starting plasma osmolality: Low
final urine: > 400
Urine osm. post-DDAVP: >400
What would be the water deprivation test result in Cranial DI
Starting plasma osm: HIGH
final urine < 300
urine osm post ddavp: > 600
Because the issue is with the brain so without water, normalises
What would be the water deprivation test result in Nephrogenic DI
Starting plasma osm: HIGH
final urine < 300
Urine osm. post-DDAVP: < 300
Doesn’t matter if no water becausse issue is with the kidneys
