Hypothyroidism

Background

3-10x more common in females
Peak incidence age >60
Emergent manifestation of severe hypothyroid = myxedema coma

Etiology

Primary
- Autoimmune (Hashimoto)
- Thyroiditis (subacute, silent, postpartum)
  - Often preceded by hyperthyroid phase
- Iodine deficiency
- After ablation (surgical, radioiodine)
- After external radiation
- Infiltrative disease (lymphoma, sarcoid, amyloid, TB)
- Congenital
- Meds
  - Amiodarone, lithium, iodine, Interferon-α, interleukin
- Idiopathic
Secondary
- Panhypopituitarism
- Pituitary adenoma
- Infiltrative causes (e.g., hemochromatosis, sarcoidosis)
- Tumors impinging on the hypothalamus
- History of brain irradiation
- Infection (e.g., tuberculosis)

Spectrum of Thyroid Disease

Thyroid physiology

Myxedema coma << hypothyroidism < euthyroid > hyperthyroidism >> thyroid storm

Clinical Features

Constitutional
- Cold intolerance, hypothermia
- Weight gain
- Weakness
- Lethargy
- Hoarse voice
- Constipation
- Dysfunctional uterine bleeding
Neuropsychiatric
- Delayed relaxation of DTRs
- Paresthesias
Cardiopulmonary
- Bradycardia
- Hypoventilation
- Pericardial/pleural effusions
Dermatologic
- Hair loss
- Non-pitting edema (periorbital, extremities)
- Facial swelling

Differential Diagnosis

Addison's disease
Chronic fatigue syndrome
Constipation
Depression
Sick Euthyroidism
Hypopituitarism
Hypothermia
Iodine Deficiency

Symptomatic bradycardia

Cardiac
- Inferior MI (involving RCA)
- Sick sinus syndrome
Neurocardiogenic/reflex-mediated
- Increased ICP
- Vasovagal reflex
- Hypersensitive carotid sinus syndrome
- Intra-abdominal hemorrhage (i.e. ruptured ectopic)
Metabolic/endocrine/environmental
- Hyperkalemia
- Hypothermia (Osborn waves on ECG)
- Hypothyroidism
  - Myxedema coma
- Hypoglycemia (neonates)
Toxicologic
Infectious/Postinfectious
Other
- Brash syndrome

Evaluation

Work-up

TSH
Total and Free T4
Total and Free T3
Thyroid Binding Globulin (TBG)
Auto-antibodies (anti-TPO, anti-microsomal, anti-Tg)
Thyroid ultrasound
ECG - bradycardia, low voltage
VBG - hypercapnia from hypoventilation, possibly compensated if chronic

Categorization

Type	Cause	TSH	FT4
Primary	Failure of thyroid	Elevated	Low
Secondary	Failure of pituitary	Low	Low
Tertiary	Failure of hypothalamus

Management

Depends on etiology
- Consider starting levothyroxine daily
  - Caution as daily doses too high may lead to thyroid storm

Disposition

Most hypothyroidism is treated as an outpatient
Admit and treat severe hypothyroidism or myxedema coma

See Also

References

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