Myxedema coma pathophysiology: Difference between revisions
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==Overview== | ==Overview== | ||
Myxedema coma occurs as a result of long-standing, | Myxedema coma occurs as a result of long-standing, un-diagnosed, or untreated [[hypothyroidism]] and is usually precipitated by a systemic illness. [[Thyroid hormone]] plays an important role in celluar [[metabolism]]. Long-standing [[hypothyroidism]] results in reduced [[metabolic rate]] and decreased [[oxygen]] consumption, which affects all [[organ systems]]. Reduced [[metabolism]] and decreased [[oxygen]] results in [[hypothermia]] and decreased drug [[metabolism]] leading to overdosing of medications particularly [[sedatives]], [[hypnotics]], and anesthetic agents and can precipitate myxedema coma. | ||
==Pathophysiology== | ==Pathophysiology== | ||
*Myxedema coma occurs as a result of long-standing, undiagnosed, or | *Myxedema coma occurs as a result of long-standing, undiagnosed, or untreated [[hypothyroidism]].<ref name="pmid28825577">{{cite journal |vauthors=Rizzo LFL, Mana DL, Bruno OD, Wartofsky L |title=[Myxedema coma] |language=Spanish; Castilian |journal=Medicina (B Aires) |volume=77 |issue=4 |pages=321–328 |year=2017 |pmid=28825577 |doi= |url=}}</ref><ref name="pmid11130234">{{cite journal |vauthors=Wall CR |title=Myxedema coma: diagnosis and treatment |journal=Am Fam Physician |volume=62 |issue=11 |pages=2485–90 |year=2000 |pmid=11130234 |doi= |url=}}</ref><ref name="pmid21941682">{{cite journal |vauthors=Mathew V, Misgar RA, Ghosh S, Mukhopadhyay P, Roychowdhury P, Pandit K, Mukhopadhyay S, Chowdhury S |title=Myxedema coma: a new look into an old crisis |journal=J Thyroid Res |volume=2011 |issue= |pages=493462 |year=2011 |pmid=21941682 |pmc=3175396 |doi=10.4061/2011/493462 |url=}}</ref><ref name="pmid17127141">{{cite journal |vauthors=Wartofsky L |title=Myxedema coma |journal=Endocrinol. Metab. Clin. North Am. |volume=35 |issue=4 |pages=687–98, vii–viii |year=2006 |pmid=17127141 |doi=10.1016/j.ecl.2006.09.003 |url=}}</ref> | ||
*Myxedema coma is usually precipitated by a systemic illness. | *Myxedema coma is usually precipitated by a systemic [[Illnesses|illness]]. | ||
===Triggers=== | ===Triggers=== | ||
*Myxedema coma can result from any of the causes of hypothyroidism, most commonly chronic autoimmune thyroiditis. | *Myxedema coma can result from any of the causes of [[hypothyroidism]], most commonly chronic [[autoimmune thyroiditis]]. | ||
*Myxedema coma can also occur in patients who had thyroidectomy or underwent radioactive iodine therapy for hyperthyroidism. | *Myxedema coma can also occur in patients who had [[thyroidectomy]] or underwent radioactive iodine therapy for [[hyperthyroidism]]. | ||
*Rare causes may include secondary hypothyroidism and medications such as lithium and amiodarone. | *Rare causes may include secondary [[hypothyroidism]] and medications such as [[lithium]] and [[amiodarone]]. | ||
===Pathogenesis=== | ===Pathogenesis=== | ||
*Thyroid hormone plays an important role in | *[[Thyroid hormone]] plays an important role in cellular [[metabolism]]. | ||
*Long-standing hypothyroidism is associated with reduced metabolic rate and decreased oxygen consumption, which affects all | *Long-standing [[hypothyroidism]] is associated with reduced [[metabolic rate]] and decreased [[oxygen]] consumption, which affects all [[organ systems]]. | ||
*Reduced metabolism results in hypothermia. | *Reduced metabolism results in [[hypothermia]]. | ||
*Reduced metabolism and decreased oxygen also results in decreased drug metabolism leading to overdosing of medications particularly sedatives, hypnotics, and anesthetic agents; this can precipitate myxedema coma. | *Reduced metabolism and decreased oxygen also results in decreased drug metabolism leading to overdosing of medications particularly sedatives, hypnotics, and anesthetic agents; this can precipitate myxedema coma. | ||
*Even in severe hypothyroidism a balance of metabolic homeostasis is achieved through adaptive neurovascular mechanisms. However in conditions such as respiratory or urinary tract infections, cardiac, acute myocardial infarction or stroke interfere with this adaptive mechanisms by decreasing the blood volume and ventilation triggering myxedema coma. | *Even in severe hypothyroidism a balance of metabolic homeostasis is achieved through adaptive neurovascular mechanisms. However in conditions such as respiratory or urinary tract infections, cardiac, acute myocardial infarction or stroke interfere with this adaptive mechanisms by decreasing the blood volume and ventilation triggering myxedema coma. | ||
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| | | | ||
*Cardiac contractility is impaired | *Cardiac contractility is impaired | ||
**Leading to reduced stroke volume | **Leading to reduced [[stroke volume]] | ||
**Low cardiac output | **Low [[cardiac output]] | ||
**Bradycardia | **[[Bradycardia]] | ||
**Hypotension | **[[Hypotension]] | ||
*Reduced stroke volume | *Reduced stroke volume | ||
**Accumulation of fluid rich in mucopolysaccharides within the pericardial sac | **Accumulation of fluid rich in [[mucopolysaccharides]] within the pericardial sac | ||
| | | | ||
*Hypotension | *[[Hypotension]] | ||
*Narrowed pulse pressure | *Narrowed pulse pressure | ||
*Edema | *[[Edema]] | ||
*Pericardial effusions | *[[Pericardial effusions]] | ||
|- | |- | ||
|Neurologic | |Neurologic | ||
| | | | ||
*Altered brain function due to | *Altered brain function due to | ||
**Reduced oxygen delivery and consumption | **Reduced [[oxygen]] delivery and consumption | ||
**Decreased glucose utilization | **Decreased [[glucose]] utilization | ||
**Reduced cerebral blood flow. | **Reduced cerebral blood flow. | ||
| | | | ||
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| | | | ||
*Central depression of ventilatory drive | *Central depression of ventilatory drive | ||
**Hypoxia | **[[Hypoxia]] | ||
**Hypercapnia | **[[Hypercapnia]] | ||
| | | | ||
*Hypoventilation | *[[Hypoventilation]] | ||
|- | |- | ||
|Renal | |Renal | ||
| | | | ||
*Reduced glomerular filtration rate because of | *Reduced glomerular filtration rate because of | ||
**Low cardiac output | **Low [[cardiac output]] | ||
**Peripheral vasoconstriction | **Peripheral [[vasoconstriction]] | ||
**Rhabdomyolysis | **[[Rhabdomyolysis]] | ||
*Low volume stimulates | *Low volume stimulates | ||
**Antidiuretic hormone impairs water excretion leading to hyponatremia | **Antidiuretic hormone impairs water excretion leading to [[hyponatremia]] | ||
| | | | ||
* Dysuria | * [[Dysuria]] | ||
* Urinary frequency | * Urinary frequency | ||
* Nocturia | * [[Nocturia]] | ||
|- | |- | ||
|Gastrointestinal | |Gastrointestinal | ||
| | | | ||
*Mucopolysaccharide infiltration and edema results in | *[[Mucopolysaccharide]] infiltration and edema results in | ||
**Malabsorption | **[[Malabsorption]] | ||
**Gastric atony | **Gastric atony | ||
**Impaired peristalsis | **Impaired [[peristalsis]] | ||
**Paralytic ileus | **[[Paralytic ileus]] | ||
**Megacolon | **[[Megacolon]] | ||
| | | | ||
*GI bleeding | *[[Gastrointestinal bleeding|GI bleeding]] | ||
*Ascites | *[[Ascites]] | ||
*Constipation | *[[Constipation]] | ||
|- | |- | ||
|Hematologic | |Hematologic | ||
| | | | ||
*Coagulopathy | *[[Coagulopathy]] | ||
**due to decrease in production of factors V, VII, VIII, IX, and X | **due to decrease in production of factors V, VII, VIII, IX, and X | ||
*Hemorrhage and vitamin B12 deficiency | *[[Hemorrhage]] and [[vitamin B12 deficiency]] | ||
| | | | ||
*Bleeding | *[[Bleeding]] | ||
*Anemia | *[[Anemia]] | ||
|} | |} | ||
Revision as of 13:35, 18 October 2017
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]
Overview
Myxedema coma occurs as a result of long-standing, un-diagnosed, or untreated hypothyroidism and is usually precipitated by a systemic illness. Thyroid hormone plays an important role in celluar metabolism. Long-standing hypothyroidism results in reduced metabolic rate and decreased oxygen consumption, which affects all organ systems. Reduced metabolism and decreased oxygen results in hypothermia and decreased drug metabolism leading to overdosing of medications particularly sedatives, hypnotics, and anesthetic agents and can precipitate myxedema coma.
Pathophysiology
- Myxedema coma occurs as a result of long-standing, undiagnosed, or untreated hypothyroidism.[1][2][3][4]
- Myxedema coma is usually precipitated by a systemic illness.
Triggers
- Myxedema coma can result from any of the causes of hypothyroidism, most commonly chronic autoimmune thyroiditis.
- Myxedema coma can also occur in patients who had thyroidectomy or underwent radioactive iodine therapy for hyperthyroidism.
- Rare causes may include secondary hypothyroidism and medications such as lithium and amiodarone.
Pathogenesis
- Thyroid hormone plays an important role in cellular metabolism.
- Long-standing hypothyroidism is associated with reduced metabolic rate and decreased oxygen consumption, which affects all organ systems.
- Reduced metabolism results in hypothermia.
- Reduced metabolism and decreased oxygen also results in decreased drug metabolism leading to overdosing of medications particularly sedatives, hypnotics, and anesthetic agents; this can precipitate myxedema coma.
- Even in severe hypothyroidism a balance of metabolic homeostasis is achieved through adaptive neurovascular mechanisms. However in conditions such as respiratory or urinary tract infections, cardiac, acute myocardial infarction or stroke interfere with this adaptive mechanisms by decreasing the blood volume and ventilation triggering myxedema coma.
Hypothyroidism | |||||||||||||||||||||||||||||||||||
Precipitating Factor | |||||||||||||||||||||||||||||||||||
↓T4 | |||||||||||||||||||||||||||||||||||
↓ IntracellularT3 | |||||||||||||||||||||||||||||||||||
Hypothalamus | Respiratory | Cardiovascluar | Renal | ||||||||||||||||||||||||||||||||
↓ Thermogenesis | Hypercapnia Hypoxia | ↓ Inotropic Bradycardia | ↓ Volume status | ||||||||||||||||||||||||||||||||
Hypothermia | Hypoventilation | ↓ Cardiac output ↓ Blood volume | ↓ GFR ↑ ADH | ||||||||||||||||||||||||||||||||
Alteration of mental state | Cerebral anoxia | ↓Arterial pressure/shock | Hyponatremia Edema | ||||||||||||||||||||||||||||||||
Myxedema Coma | |||||||||||||||||||||||||||||||||||
The following table summarizes the various effects of reduced thyroid hormone on different organ systems
Organ System | Effect due to Decreased Thyroid Hormone | Manifestation |
---|---|---|
Cardiovascular |
|
|
Neurologic |
| |
Pulmonary |
|
|
Renal |
|
|
Gastrointestinal |
|
|
Hematologic |
|
Associated Conditions
Common conditions associated with myxedema coma include:
- Type 1 diabetes
- Addison's disease
- Pernicious anemia
- Vitiligo
- Rheumatoid arthritis
- Premature ovarian failure
References
- ↑ Rizzo L, Mana DL, Bruno OD, Wartofsky L (2017). "[Myxedema coma]". Medicina (B Aires) (in Spanish; Castilian). 77 (4): 321–328. PMID 28825577. Vancouver style error: initials (help)
- ↑ Wall CR (2000). "Myxedema coma: diagnosis and treatment". Am Fam Physician. 62 (11): 2485–90. PMID 11130234.
- ↑ Mathew V, Misgar RA, Ghosh S, Mukhopadhyay P, Roychowdhury P, Pandit K, Mukhopadhyay S, Chowdhury S (2011). "Myxedema coma: a new look into an old crisis". J Thyroid Res. 2011: 493462. doi:10.4061/2011/493462. PMC 3175396. PMID 21941682.
- ↑ Wartofsky L (2006). "Myxedema coma". Endocrinol. Metab. Clin. North Am. 35 (4): 687–98, vii–viii. doi:10.1016/j.ecl.2006.09.003. PMID 17127141.