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
- Hypoglycemia (neonates)
- Toxicologic
- Infectious/Postinfectious
- Other
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
- Consider starting levothyroxine daily
Disposition
- Most hypothyroidism is treated as an outpatient
- Admit and treat severe hypothyroidism or myxedema coma
See Also
- Myxedema coma
- Thyroid (Main)
References
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