Thyroid disorders Flashcards
(41 cards)
What are the functions of the thyroid gland?
- Produces 2 hormones (T4, T3)
- Regulates metabolism
- Affects every cell in body
What is hyperthyroidism?
- Too much thyroid hormone
- Metabolism speeds up
What is hypothyroidism?
- Too little thyroid hormone
- Metabolism slows down
What is Goitre?
- Enlargement of thyroid
- Can be diffuse or nodular
How is hyperthyroidism diagnosed?
Suppressed TSH is hallmark of hyperthyroidism:
- Measurement of FT3 will be necessary in patient with C/F of hypertyroidism
- Suppressed TSH
- Normal FT4
Called T3 toxicosis usually seen in MNG
Patient with overt opthalmopathy, no additional testing required:
- Isotope utake studies - Increased uptake in hyperthyroidism, lack of uptake in thyroiditis and iodine ingestion. In MNG it serves to define the functional characteristics of the gland
- Thyroid USS
- Thyroid antibody assays
Performed in selected cases only
What are the investigations for hyperthyroidism?
- Assays of fT4, TSH
- Autoantibody assays - TPO, TSH
- Imaging
- Ultrasound
- Nuclear medicine
How is hypothyroidism investigated?
- Serum assays - fT4, TSH
- Hallmark is increased TSH, antedates decline in fT4
- Autoantibody assays - TPO, thyroglobulin
- Presence of antibodies will confirm autoimmune thyroiditis as cause
- Can occur in association with other autoimmune disorders, pernicious anaemia or Addisons’
- Mild anaemia
- Increase CK
- Abnormal lipids with high total and LDL cholesterol
- Imaging
- Ultrasound
- Nuclear medicine
Describe serum markers and thyroid nodules
Serum TSH guides further management
Serum calcitonin:
- Sensitive marker of C-cell hyperplasia/MTC
- Screening not recommended in UK and US but routinely done in EU
- Useful in FU of MTC
Serum thyroglobulin:
- Not sensitive/specific for diagnosis of thyroid malignancy
- Useful in FU of differentiated thyroid cancer
Describe ultrasound scan for thyroid nodules
- Rationalise thyroid US/FNA
- Suggested standards for reports
- Indications for FNA
- Based upon US scoring system
- U1-U5
- Follow up based upon US appearances
Which thyroid nodules require FNAB?
- U1-2: FNA not required unless high risk
- U3-5: US guided FNA
- FNA of abnormal lymph nodes (diagnosis/staging)
- Incidental nodules on CT: clinical evaluation and futher Ix (US) in high risk groups
- PET-CT positive nodules: US and FNA - higher risk of malignancy
What are signs and symptoms of hyperthyroidism?
- Nervousness
- Irritability
- Difficulty sleeping
- Bulging eyes/ unblinking stare
- Goitre
- Menstrual irregularities/light periods
- Rapid irregular
- Hoarseness or deepening of voice
- Persistent sore or dry throat
How is hyperthyroidism treated?
- Antithyroid drugs (ATD)
- Radioiodine (131 I) - Safe and appropriate treatment in nearly all types hyperthyroidism, especially in elderly. Contraindicated inchildren, pregnancy, women who are breast feeding
- Women of childbearing age should wait 4 months after 131 I before becoming pregnant. Should be used with caution in patients with opthalmopathy. Use prophylactic steroids and avoid hypothyroidism
- Subtotal thyroidectomy
Treatment regimens:
- CMZ typical starting does 15-40mg o.d
- PTU starting dose 100-600m t.d
- Titrate treatment against serum T4 concentrations at 4-6 weeks to a maintenance dose
- Follow up at 3-4 months interval
- For aim of remission treatment has to be used 12-24 months
- Long term remission can be achieved in 50-60% cases
Factors to consider:
- Age
- Size of goitre
- Presence of co-existing condition
Drugs safe in pregnancy. Possible association carbimazole with fetal aplasia cutis. Some physicians may substitute PTU for CMZ in pregnancy. No contraindications to breast feeding. PTU excreted less in breast milk. Patients receiving CMZ in dose 20mg or less need not be changed to PTU
In patients with hyperthyroidism and low 131 I uptake none of the therapies is indicated:
- Thyoiditis generally resolves spontaneously
- B-blockers usually sufficient to control symptoms
- NSAIDs
- Steroids
What are indications for surgical treatment of hyperthyroidism?
Objective to cure hyperthyroidism w/o making patient hypothyroidism
Indications:
- Large Goitre
- Failed medical treatment
- Non compliance
- Side effects
- Patient preference
- Multinodular goitre
Describe subclinical hyperthyroidism
- Persistently suppressed TSH with normal FT4 and FT3 in a patient with no symptoms
- No consensus whether such patients should e treated
- ? Significant morbidity through higher risk of AF in patients over 60 and decreased BMD in postmenopausal women
Describe normal/raised TSH and raised FT4 or FT3
- Interfering antibodies to thyroid hormones
- Intermittent T4 therapy or T4 overdose
- Resistance to thyroid hormone
- TSH secreting pituitary tumour
- Amiodarone
- Acute psychiatric illness
- Familial dysalbuminaemic hyperthyroxinaemia
Describe anti-thyroid antibody interference
Suspect if FT4 and FT3 assays widely disconcordant with each other
Usually evidence of thyroid autoimmunity
Anti-T4 and anti-T3 antibodies more commo in free than total thyroid hormone assays
Determine free thyroid hormone lvls by eqm analysis where confounding antibody is excluded by dialysis membrane
Thyroid function can be monitord by TSH once interference confirmed
Describe thyroid hormone resistance
- Syndrome of reduced responsiveness of target tissues to thyroid hormone
- Thyroid hormone receptor mutations
- Usually family history of thyroid hormone resistance or goitre (dominant)
- Absence of usual symptoms/consequences
- Absence of pituitary tumour on MRI
- Normal SHBG
- Normal/exaggerated response to TRH
- Normal alpha-subunit/TSH ratio
- Thyroablative treatment not indicated
Describe the effects of drugs on the thyorid
- Synthesis and secretion - iodinated drugs, lithiium salts, cytokines
- Transport - Steroids, diuretics, FFA, NSAID, heparin
- Metabolism - P450 inducers, 5’DI inhibitors: PTU, B-blockers, dexamethasone, iodinated drugs
- Action - Amiodarone, phenytoin
Describe the management of patients taking amiodarone
- Regulate testing in patients which may be difficult to detect clinically due to fact amiodarone can result in both hypo and hyperthyroidism
- Testing recommended in patients with evidence of deteriorating cardiac function or weight loss
How is type 1 and type 2 hyperthyroidism differentiated?
TESTS:
- Goiter - In type 1, it’s moltinodular or diffuse, but in type 2 there’s none or it’s small diffuse
- 24H-RIU - In type 1, normal, high or low, in type II, undetectable
- IL-6 - Type 1 low, type 2 high
- Doppler - Type 1 increased vascularity, type 2 absent vascularity
- Thyrotropin receptor antibodies - Type 1 Yes- Graves’ disease, type 2 no.
How are type 1 and tye 2 hyperthyroidism treated?
Type 1:
- Carbimazole high dose
- Perchlorate
- Lithium
- Radioiodine
- Thyroidectomy
Type 2:
- Prednisolone
- Carbimazole
Describe thyroid FNA
- Considered most cost effective and sensitive/specific diagnostic test of thyroi nodules
- Use of US has expanded the role of FNA in evaluating nodules and improved validity of results
Possible FNA results:
- Benign: 70 -75 %
- Malignant: Up to 5%
- Suspicious: About 10%
- Nondiagnostic: About 10 - 20%
What are the limitations of thyroid FNA?
False negatives: (< 5% of FNA) more likely in large (>4cm) or small (<1cm) nodules
Suspicious FNA (Follicular and Hurhtle cell neoplasm): cannot distinguish benign vs malignant of hypercellular nodules by FNA alone, ALWAYS require surgical pathology for dx (up to 10 – 30% of these will be CA)
Non-diagnostic results: NEVER consider equivalent to benign, up to 10% of ND FNA will contain CA on resection
How is hypothyroidism diagnosed?
In hypothyroidism, C/F non specific, appear insidiously and often attributed to aging
- Ideally baseline serum TSH
- Transient hypothyroidism in infants of women treated during pregnancy
