Thyroid CHapter Flashcards
1
Q
Thyroid
A
Micro L Cystic Peripheral vascularutt Round shape —-
2
Q
Type 1 deiodinase
A
Outer and inner Ring
3
Q
Deiodinase
Subcellular location in endoplasmic reticulim
A
Type 2
4
Q
Deiodinase
Outer ring
A
Type 2
Type 1 outer and inner
5
Q
Deiodinase
High susceptibility to PTU
A
Type 1
Inner and outer - inhibited by PTU and activated by thyroid hormone
6
Q
Deiodinase
Decreased response to increased T4 (the rest increases)
A
Type 2
7
Q
Deiodinase
Source of plasma t3 in thyrotoxic patients
A
Type 3
8
Q
Deiodinase
Found in liver kidney thyroid pituitary
A
Type 1
9
Q
Effects of thyrotoxicosis in CV system
A
> decreased peripheral vasc resistance to dissipate heat
> inc CO inc HR inc SV
10
Q
Mechanism of increased cardiac contractility in thyrotoxicosis
A
Increase in ratio of alpha to B myosin chain
11
Q
Mearns Lerman scratch
A
Scratchy systolic sound in left sternal border resembling a pleuripericardial friction rub found in thyrotoxicosis
12
Q
% of px with unexplained atrial fibrillation who are thyrotoxic
A
15%
13
Q
Percent of px with thyroxtoxicosis who have atrial fibrillation
A
2-20%
14
Q
Most common thyroid neoplasm
A
Follicular adenoma
15
Q
Dose of rTSH
A
0.01 to 0.03 mg
16
Q
TNM scoring
T4
A
T0 no evidence of prary tumor T1 <1 T2 2-3 T3 4 cm limited to thyroid T4 extending beyond the thyroid
17
Q
Most impt cytologic variant of thyroid CA whicb composed predominantly entirely of large cells with granular eosinophilic cytoplasm
A
Oxyphilic / oncocytic/ hurthle cell adenoma
alignant
18
Q
PTC variant with poor progmostic finding
A
Hobnail variant with micropapillary pattern
19
Q
PTC variant cells twice as tall as they are wide
A
Tall cell variant
20
Q
PTC variant prominent nuclear stratification of elongated cells
A
Columnar cell variant
21
Q
Aggrassive variants
A
Tall cell
Columnar cell variant
22
Q
Nuclear changes in FNA
A
Nuclei are larger than N folloculae cells and overlap
Fissured like coffee beans
Ground glass nuclei (Chromatin hypodense)
Contain an inclusion corresponding to cytoplasmic invagination
23
Q
Protooncogene whose activation is found only in PTC
A
RET
24
Q
Where is RET found
A
Chr 10q11-2
25
% of thyroid malignancies that are medullar
5%
26
Mutation found in tall cell bariant of PtC
BRAF
Associated with higher risk of recurrence
27
Age papillary thyroid CA
30- 50 yrs
28
Female predominance of ptca
80
29
FTC
Invasion of capsule blood vessel or adjacent thyroid
30
CA more common in areas with iosine deficiency
Folliculae CA
31
Oncogene in FTCs
RAS oncogene
32
Cytogenetic abnormality limited to FTC
P arm chromosome 3
33
Age anaplastic thyroid CA
After 60 yrs
FTC- 50 yrs ave
34
Hypothyroidism without a goiter
Atrophoc thyroiditis
35
Commonest cause of goiter in iodine sufficient regions
Hasimotos
36
Presence of this may be a favorable prognostic factor in patients with papillary CA
Hashimoto
37
Suspected in hashimoto px witb painful enlargement of the thyroid gland
Occurs almost exclusively in hasimoto patients
THYROID LYMPHOMA
38
Impairment of intrathyroidal Nd peripheral deiodination of iodotyrosines
Ipdotyrosine dehydrogenase defect
| DEHAL1B gene
39
Unusual cause of hypothyroidism that has been identified in infants with visceral hemangiomas
Consumptive hypothyroidism
40
Contained in cassava
Linamarin
41
Tsh goal of treafment in Hashimoto
Tsh in the lower half of the reference interval
42
Action of lithium and why it causes hypothyroidism
Inhibits thyroid hormone release
| In high concentrations can inhibit organic binding reactions
43
Pendred syndrome
Defect in iodine organificatkon and sensory nerve deafness
44
Difference in finding:
| Painful versus painless subacute thyroiditis
Painful- small and atrophic
| Painless- enlarged and dfirm infiltraion
45
% of thyroid independent of pituitary
| Why central is leas severe than primary hypothyroidism
10-15%
46
Expressed by visceral hemangiomas
D3
47
Defects in this gene causes hereditary hypothyroidism
POUf1 Nd prop 1
48
More common type of mutation in RTH (resistance to thyroid hormone)
Mutation in thyroid hormone receptor B
| Interferes capacity of receptor to respond normally to T3
49
Presentation of patients witb RTH
Mix of hyper and hypo
Palpitations and tachy
Growth retardation
50
Profile of RTH patient
inc ft4
N or alightly increased tsh
Tachy
Goiter
51
Treatment of RTH
TRIAC
52
Time required for complete equilibriation of FT4
6 weeks
53
% of levothyroxine absorbed in stomach
80%
54
Px with impaired gastric acid secretion require higher dose levothyroxine
How higher
22-34% higher
55
Dose adjustment thyroid hormone in Elderly because thyroid hormone clearance is decreased
20-30% less
56
Increase thyroid hormone requirement in pregnancy
First trimester
57
Reasons for the increase req of thyroid hormone in the first trimester of pregnancy
- increased T4 binding
- increased volume of distribution of T4
- increase in D3 in placemta
58
Dose levothyroxine myxedema coma
Levothyroxine 500-800 IV
Then 100 IV thereafter
Hypertonic Saline!!!
IV liothyrosine 25 ug q12
59
Rx reidel thyroiditis
Tamoxifen
60
Acute thyroiditis VS Subacute thyroiditis
Preceding upper respiratory infection
Fever
Sorethroat
Acute
61
Acute thyroiditis VS Subacute thyroiditis
| Paiful thyroid swelling
100- acute
| 77- subacute
62
Acute thyroiditis VS Subacute thyroiditis
| Left side affected
Acute
63
Acute thyroiditis VS Subacute thyroiditis
| Migratory thyroid tenderness
Sibacute
64
Acute thyroiditis VS Subacute thyroiditis
Abnormal thyroid hormone levels
Elevated or depressed
Subacute
65
Acute thyroiditis VS Subacute thyroiditis
FNAB
Purulent bacteria fungi
Acute
In subacute - lymphocytes macriphage giant cells
66
Acute thyroiditis VS Subacute thyroiditis
| Response to GC treatment
Acute transient
| Subacute 100%
67
Acute thyroiditis VS Subacute thyroiditis
| Gallium scan positive
Both
68
Thyroid fibrosis in middle aged women
Riedel chronic sclerosing thyroiditis
69
Tissue location of type 1 deiodinase
Liver
Kidney
Thyroid
Pituitary
Type 2
Cns brown adipose tissue heart skeletal muscle placenta
Tupe 3 placenta cns hemangiomas
70
Half life of T 3
0.75 days
71
The most impt thyroid hormone inactivating emzyme
D3
Inner ring deiodinase
72
Recommended iodine dose pregnant
200 ug
Adults 150 ug
Children 90-120 ug
73
Naturally occuring I
I 127
74
Suggested starting dose of MMI in the setting of AIT
Ata guidelines
40 mg OD
75
How are T3 and T4 transported across cellular membranes
MCT8
| MCT10
76
Proteins facilitating transport of T4 and T3 across cell membranes
Mct8 and mct10
77
Transport of T4 across blood brain barrier
OAYP1C1
78
Mutation in the MCT8 gene
Mental retardation
Increased T3
Dysarthria
Athetoid movements
Allan Herndon Dudley Syndrome
79
Rx for mct8 gene mutation
```
PTU with LT4
Diiosithyropropionic acid (DITPA)
```
80
Most impt pathway for T4 metabolism
Outer ring
D1 and D2
And is 80% of the source of T3 for humans
81
Diff of D1 Nd d2
D1 hugher Km
Prefers T3 Nd T3so4
Inhibited by PTU
Increased by thyroid hormone (D2 decreased)
82
To convert T4 nmol to ug/dl
Divide by 12.87
83
Half lfe of TBG
5 days
84
% of T3 bound by TBG
T3 80%
| T4 64 %
85
Blocks synthesis of TBG
L asparaginase
86
Major thyroid hormone binding protein in the csf
Transthyretin (TTR)
Found in choroid plexus
87
Moa if iopanoic and iopodipie acid
Inhibit deiodinases
88
Iodine per drop of sski
38 mg/drop
Lugols 6 mg/drop
89
Quantity of iodine required to supress tadioactive iodine to <2
> 30 mg/day
90
Iodine content per iodized salt
760/10 g
91
Iodine content angiographic and CT dyes
400-4000 mg/dose
92
How growth hormone affects thyroud
Decrease D3 activity outer ring deoidination
93
Biochemical markers of thyroid status
| Decreased during thyrotoxicosis
Low low
LDL
Lipoproteins
94
Biochemical markers of thyroid status
| Increased during thyrotoxicosis
```
Vw
Osteocalcin
Urine pyridium
Ferritin
ALP
Sex hormone BG
ANP
```
95
Decreased during hypothyroidism
Vassopressin
96
Spared graves ophthalmoplegia
Muscle tendons spared
| With lateral rectus least commonly affected
97
10 mg carbimaxole is metabolized to ___
6 mg methimazole
98
Multinodular toxic goiter
12-14 mci
99
Transient thyrotoxicosis where thyroid tenderness is the most prominent symptom and thyrotoxicosis is rare
Viral thyroiditis
Subacute
De quervain
Granulomatous
100
Histopath subacute thyroiditis/
| Giant cell thyroiditis
Well developed follicular lesion that consists of cebtral core of colloid surrounded by multinucleated giant cells
101
(+) sudden appearance of pain in region of thyroid gland wuth or without fever
Aggravated by turning head or swallowing radiates to ear and occiput
Subacute thyroiditis
De quercain
Granulomayous
Giant cell
102
Viral infection of thyroid gland preceded by URTI
Subacute thyroiditis
103
Differentiate acute exacerbation if hasgimito thyroiditis and de quervain/ subacute thyroiditus
Lack of elecation if ESR in hasimotis
104
Rx compromised Cv function hypothyroid
DITPA
105
Acute thyroiditis commonly affects which lobe
Left lobe
106
1 mCi= __ MBq
37
107
Preferred substrate of D1
rT3
| T3 SO4
108
An excess of thyroid hormone increases this deiodinase
D1
| D2- reduced by thyroid hormones
109
Deiodinase with Half life of 20-30 mins
D2
| D1 and D3 has long half life (more than 12 hrs)
110
Source of TRH
Parvocellular region of paracentricular nuclei
111
Hormone picture of thyroid hormone resistance
Elevated FT4 ans TSH
112
Enzyme in the CNS that rapidly degrades TRH
protein peptidase II
- exclusively !
113
Riedel’s thyroiditis may be treated with this drug
Tamoxifen
114
How does somatostatin affect TSH secretion
Inhibits TSH
So does:
- Dopamine
- Bromocriptine (dopamine agonist)
115
Half life of TSH
30 mins
116
Is FT3 the only one capable of activating thyroid hormone receptors thats why it is called the active thyroid hormone?
Nope, however it binds TRs with 15x affinity compared to FT4 explaining its function as the active thyroid hormone
117
Iodine per drop of lugols
6 mg/ drop
118
Iodine per tab of amiodarone
75-200 mg
119
Iodine in prenatal vitamins
150 ug/tab
120
Responsible for the escape / adaptation phenomenon in wolf chaikoff
Decrease in NIS expression causing decrease in iodide transport activity
121
Why should chronic high iodine intake during pregnancy be avoided?
The escape phenomenon does not occur in the 3rd trimester fetus—> hypothyroidism
122
Daily iodine requirement in the newborn
10 ug/kg
123
Effect of gonadal steroids on the TBG and TSH
Estrogen - inc TBC- inc TSH
| Androgen- dec TBG
124
What are the other hormones that can affect thyroid function
1. Glucocorticoids
2. Gonadal steroids
3. Growth hormone
125
Normal TSH
0.4 to 4.2 mU/L
126
Normal range
| FREE T4
9- 30 pmol/L
| 0.7 to 2.5 ng/dL
127
Normal range Free T3
3-8 pmol/L
| 0.2 to 0.5 ng/dL
128
Thyroid hormone profile of sick euthyroid syndrome :
Is like central hypothyroidism
Dec FT3 then Dec Ft4
and TSH from Normal, decreases
On recovery phase, TSH increases first so the profile is like primary hypothyroidism
129
TBG jn pregnancy / neonatal state / OCPd estrogen tamoxifen
Increased binding of TBG
130
Biochemical markers increased in thyrotoxicosis
“VOUFASA” table
```
VWF
Osteocalcim
Urine pyridium collagen cross links
ferritin
ALP
SHBG
ANP atrial natriuretic peptide
```
131
Biochemical markers decreased in thyrotoxicosis
LDL
| Lipoprotein a
132
Biochemical markers decreased in hypothyroidism
Vasopressin
133
This thyroid autoantibody is not found in the general population
TSHR -Ab
Found in 95 percent of graves disease
Tg-Ab 20% normal
Anti TPO 27% normal pop
134
Half life of iodine 131
8.1 days
135
Half life of iodine 123
0.55 day
136
Define iodine deficiency
Urinary iodine excretion less than 100 ug/day
137
States associated with increased RAIU aside from hyperthyroidism
- aberrant hormone synthesis
- iodine deficiency
- response to thyroid hormone depletion (rebound after antithyroid therapy)
- excessive hormone loss (nephrotic syn, chronic diarrhea, ingestion of soybean, cholestyramine)
138
Prevalence of hyperthyroidism
1-2% in women
139
Reason for the retraction of the upper and lower eyelids in hyperthyroidism
Increased adrenergic tone
140
Clotting factor increased in thyrotoxicosis
Factor VIII
But note that the clotting mechanism is normal
141
Effect of thyrotoxicosis on warfarin
Enhanced sensitivity to warfarin because there is accelerated clearance if vitamin K dependent clotting factora
142
Drug induced thyroiditis
Sunitinib
| Sorafenib
143
Treatment of subacute thyroiditis
Glucocorticoids (pred 40 mg/day)
Aspirin / NSAIDs
if tsh is not suppressed you may add Levothyroxine
144
Thyroid hormone profile of thyrotoxicosis factitia
Dec TSH
INC FT4 and FT3
Increased Tg
Normal RAIU
145
Complications of RAI
- thyroid cancer
- mortality
- hypothy (80 in 6 mos)
- radiatjon thyroiditis (exacerbation of thyrotoxicosis 10-14 days after RAI)
146
When should anti thyroid agent be withdrawn prior to RAI
3-7 days
147
Goal of hyperthyroidism treatment during pregnancy
Maternal free T4 level just above the Upper normal nonpregnant range
NO ATTEMPT TO NORMALIZE TSH
thyroid drugs may overtreat fetus compared to the mother
148
Period of risk of embryopathy of thyroid drugs
6-10 weeks pregnancy
149
Hallmark of the immune effects initiated by the placenta
Fall in thyroid autoantibody secretion
150
When does FT4 rise in pregnancy
Near the end of first trimester and is accompanied by partial TSH suppression
