[PPT] - Hypothyroidism Pathophysiology, differentials, investigations and PowerPoint Presentation

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Hypothyroidism

Endocrinology series

Dr Azeem Alam, MBBS BSc (Hons) Surgical AFP Guy’s and St. Thomas’ Hospital

Content reviewed on the 26/04/2020.

Pathophysiology, differentials, investigations and management.

Cases Quiz

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History A 36-year-old Caucasian female presents to her GP in London with ongoing fatigue. She has also gained a significant amount of weight and has been constipated recently. She looks tired and you note that she is wearing a woolly hat, despite it being a warm, summer’s afternoon. Observations HR 56, BP 126/84, RR 16, SpO2 98%, Temp 37.4°C.

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Case 1

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History A 36-year-old Caucasian female presents to her GP in London with ongoing fatigue. She has also gained a significant amount of weight and has been constipated recently. She looks tired and you note that she is wearing a large coat, despite it being a warm, summer’s afternoon. Observations HR 56, BP 126/84, RR 16, SpO2 98%, Temp 37.4°C.

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Case 1

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Pathophysiology

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Definition: a deficiency in circulating thyroid hormone. Thyroxine (T4) and tri- iodothyronine (T3).

Aetiology

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Primary hypothyroidism

95% of cases
Iodine deficiency
Autoimmune thyroiditis
Transient thyroiditis

TSH Free T4 Overt hypothyroidism ↑ ↓ Subclinical hypothyroidism ↑ ↔

Aetiology

Primary hypothyroidism

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Primary hypothyroidism Features Iodine deficiency Commonest cause worldwide Hashimoto’s thyroiditis (autoimmune) Commonest cause in the developed world

Autoimmune (anti-TPO antibodies)
Diffuse painless goitre
Transient thyrotoxic state,

hashitoxicosis

Increased risk of non-Hodgkin

lymphoma Subacute (De Quervain’s) thyroiditis (transient)

Viral prodrome
Transient thyrotoxic state
Painful goitre
Raised inflammatory markers
Self-limiting

Aetiology

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Categorisation Causes Primary hypothyroidism

Iodine deficiency
Autoimmune thyroiditis
Transient thyroiditis
Drugs
Post-ablative therapy or

surgery

Infiltrative disorders
Congenital

Aetiology

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Secondary (central) hypothyroidism

Pituitary or hypothalamic disorder

Aetiology

TSH Free T4 Secondary hypothyroidism ↓ or ↔ ↓

Secondary hypothyroidism

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Categorisation Causes Secondary hypothyroidism (central)

Pituitary adenoma or glioma
Pituitary surgery or radiation
Vascular disorders
Pituitary apoplexy
Sheehan syndrome
Hypothalamic disorders
Infiltrative disorders
Drugs

Aetiology

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Prevalence of any cause of hypothyroidism is 1-2%, with Hashimoto’s thyroiditis being the most common cause.

Female gender: 15-20x more frequent
Middle-aged: peak age is 30-50 years old
Family history
History of autoimmunity: e.g. pernicious anaemia or T1DM
Chest or neck irradiation
Thyroidectomy or radioiodine

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Epidemiology

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Clinical features

Symptoms Signs Weight gain Bradycardia Cold intolerance Goitre Lethargy Loss of lateral aspect of eyebrows Dry skin Hair loss Constipation Hyporeflexia Menorrhagia: later develop

ligomenorrhoea and

amenorrhoea

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Clinical features

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Primary investigations:

TFTs: decreased T3/T4 and increased TSH in primary hypothyroidism
Antibodies: anti-TPO antibodies associated with Hashimoto’s thyroiditis (95%)
Inflammatory markers: raised in De Quervain’s thyroiditis

Investigations to consider:

Ultrasound: if there is a goitre or focal nodule and malignancy is suspected
Radionucleotide scan: not routine
FBC and serum B12 level: assess for possible pernicious anaemia
Fasting lipids: hypothyroidism is associated with hypercholesterolemia
Serum glucose and HbA1c: hypoglycaemia and T1DM
Coeliac serology: assess for coeliac disease

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Investigations: stable patient

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Investigations: autoantibodies

Thyroid autoantibodies Autoantibody Condition Prevalence Anti-TSH receptor Graves’ disease 90-100% Hashimoto’s thyroiditis 0-5% Anti-TPO Graves’ disease 70-80% Hashimoto’s thyroiditis 90-95% Anti-thyroglobulin Graves’ disease 20-40% Hashimoto’s thyroiditis 30-50%

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Overt hypothyroidism:

Levothyroxine (T4): offer levothyroxine with regular review of symptoms and TSH

every 3 months Subclinical hypothyroidism:

Depends on the age, symptoms and TSH [3]
TSH > 10 mU/L and normal T4: consider levothyroxine
TSH < 10 mU/L and normal T4: consider 6 month trial of levothyroxine if symptomatic

and < 65 years old

In all other cases observation is indicated

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Management

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Extreme manifestation of hypothyroidism
> 60 years old
Causes: hypothermia, infections (e.g. influenza), medication (e.g. amiodarone),

surgery, trauma

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Myxoedema coma

Symptoms Signs Long-standing hypothyroid symptoms Bradycardia and hypotension CNS: confusion, psychosis, apathy Hypothermia: often < 35.5°C Constipation Myxoedematous face Hypoventilation

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Bedside

ECG: bradycardia

Bloods

TFTs: raised TSH and reduced T4
FBC: normocytic normochromic anaemia
U&Es: hyponatraemia and deranged renal function
ABG: hypoxia, hypercapnia, respiratory acidosis
Blood glucose: hypoglycaemia
Infection screen

Investigations to consider:

Lipid profile: hyperlipidaemia
Serum cortisol: exclude adrenal insufficiency

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Myxoedema coma: investigations

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General measures

ITU or HDU
NIV or mechanical ventilation: may be required
Correct hypoglycaemia and electrolyte disturbances
Slow warming

Specific measures

IV thyroid hormone replacement: often levothyroxine alone (100-500 μg), but

controversial

Antibiotics: many advocate broad-spectrum antibiotics
IV hydrocortisone: assume adrenal insufficiency until excluded (100 mg)

Mortality: 50% even if promptly treated Poor prognosis: elderly, hypothermic and bradycardic

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Myxoedema coma: management

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