Transcript PPT File

Tutorial 1
Pituitary & Thyroid
Disorders
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Case 1 :
James is a 5 –year- old child. He is much smaller than his
classmates at school . His growth rate has been monitored
and has clearly dropped off markedly in the past year. He is
an active. On examination he has normal body proportions.
His mother and father are of average height. His bone age
is that of a 3- year- old child.
What biochemical tests would be appropriate in the
investigation of this boy?
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Answer of case 1:
Growth hormone deficiency should be suspected particularly in view
of the documented fall-off in the patient’s growth rate over the
previous year.
Random growth hormone measurement is potentially misleading i.e.
false positive and false negative results are frequent.
Thus , many endocrinologists measure the following :
1- Exercise- stimulated GH where a result > than 20 mU/l excludes
GH deficiency.
2- Also, Clonidine ,a potent stimulant of GH secretion can be
diagnostic.
3- Response of GH to insulin-induced hypoglycemia can also be used
but it has been abandoned by some centers as a diagnostic test for
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children
because of its hazards.
Case 2 :
A 36 year old man complained of impaired vision while driving,
particularly at night. After clinical and initial biochemical assessment, a
combined anterior pituitary stimulation test was performed.
( i.v. insulin 0.1 U/Kg , TRH :200 µg , GnRH: 100 µg )
Reference values
Time Glucose
(min) mmol/l
Cortisol
nmol/l
GH Prolactin LH
mU/l
U/l
fasting glucose
2.8 – 6.0 mmol/l.
Cortisol
at morning:140 – 690 nmol/l
at night : < than 100 nmol/l
0
3.6
320
1.5
17000
<1
30
0.9
310
1.7
16400
3.7
60
1.8
380
1.6
18000
3.7
90
2.7
370
1.4
120
3.3
230
1.4
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Growth hormone
following glucose:
< than 2 mU/l.
following stress:
> than 20 mU/l.
Prolactin
50 -400 mU/l.
LH
adult male:2 – 10 U/l
Questions:
1-A lower than normal dose of insulin was used . Why ?
2-What is the most likely diagnosis ?
3-What precautions should be taken before surgery?
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Answer of case 2:
1- If hypopituitarism is suspected, a lower dose of insulin
should be used. This is because the relative deficiency of
glucocorticoids and growth hormone are associated with an
increase in insulin sensitivity.
2- The basal prolactin was so high in the case that
hyperprolactinoma was the diagnosis until proven otherwise.
Also, imaging of the pituitary confirmed the diagnosis.
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3- The hypoglycemic stress induced in the patient did not
cause the expected rise in serum cortisol (it should rise
to more than 500 nmol/l in response to insulin stress test)
therefore, it is essential that he is commenced on steroid
replacement before surgery.
4- As hyperprolactinaemia frequently shrink dramatically
in response to dopamine agonists, he should be
commenced preoperatively on bromocriptine to reduce
the size of the tumor.
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Case 3 :
A 49-year-old woman receiving hormone replacement
therapy was found to have a thyroid nodule . No
lymphadenopathy was detectable and clinically she
appeared to be euthyroid. A technetium scan revealed a
cold nodule and an ultrasound scan indicated it was cystic.
Biochemistry results in a serum specimen:
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T4
(nmol/l)
172
Reference range:
70 -150 nmol/l.
TSH
(mU/l)
0.4
Reference range:
0.3 – 5.0 mU/l.
Questions:
1- Explain why the T4 is elevated ?
2- What other investigations should be performed
on this patient ?
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Answer of case 3:
1- This patient has a high serum T4 because of the
estrogen component of hormone replacement therapy
stimulates the synthesis of thyroxine-binding globulin.
2- By far the most important investigation for this woman is
a fine needle aspiration biopsy of the thyroid nodule. It is
important that thyroid epithelium is obtained to enable the
diagnosis of thyroid cancer to be excluded or confirmed.
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Case 4 :
Investigation of a 63-year-old woman with effort angina revealed a
serum TSH of 96 mU/L (normal=0.3 – 5.0 mU/l) and a serum free T4
of 3.7 pmol/L (normal 10-27 pmol/l) .
An ECG showed some evidence of ischemia but was not diagnostic
of myocardial infarction.
Further biochemical investigation revealed :
Cholesterol
(mmol/L)
9.3
Creatine kinase 290
(U/L)
AST
(U/L)
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35
Reference ranges:
< than 5 mmol/L.
< than 90 U/L.
10 – 40 U/L
How should these results be interpreted ?
Answer of case 4:
1- The low free T4 and markedly elevated TSH results
suggest Primary Hypothyroidism . Skeletal and Cardiac
muscles are affected in hypothyroidism causing the release
of creatine kinase into the circulation. This, combined with a
decrease in the catabolic rate of creatine kinase ,will be
sufficient to cause the creatine kinase to increase to the
levels observed in this case.
2- The AST is at the upper limit of the normal reference and
this will fall along with creatine kinase and cholesterol after
a few weeks of treatment with thyroxine.
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Case 5 :
A 28-year-old woman with thyrotoxicosis has had two
courses of carbimazole. Results from her recent visit to
the thyroid clinic now show:
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TSH
(mU/L)
< 0.05
Reference range
0.3 -5.0
T4
(nmol/L)
210
Reference range
70 -150
free T4
(pmol/l)
66
Reference range
10-27
1- What has happened ?
2- What other biochemistry tests might be useful here ?
Answer of case 5:
It is likely that this patient has suffered a relapse of her
thyrotoxicosis .
The severity of the derangement in her thyroid
biochemistry (free T4 : 66 pmol/l) makes it likely that she
will be clinically thyrotoxic and symptomatic .
Repeated failure of medical therapy may allow us to think
of alternative treatment such as radioactive iodine and
surgery .
N.B. :
Radioactive iodine ablates the production of thyroid
hormone irreversibly and the patient would need to take
replacement thyroxine therapy permanently thereafter.
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