Can hypothyroidism be associated with hypertension?

Short answer: Yes! Just as hyperthyroidism, hypothyroidism is also associated with hypertension (1-5). Compared to normal subjects, patients with hypothyroidism have a 3-fold increased prevalence of hypertension, usually diastolic (2). In fact, hypothyroidism has been identified as a cause of hypertension in 3% of patients with high blood pressure and is the most common cause of secondary hypertension after renovascular hypertension (1-3).

 
High systemic vascular resistance and increased arterial stiffness are among the important mechanisms explaining hypothyroid-induced hypertension (1). High systemic vascular resistance is thought to be due to the absence of the vasodilator effects of T3 on vascular smooth muscle and decreased response to beta-adrenergic stimulation, which in turn leads to increased alpha-adrenergic responses. Increased arterial stiffness may also contribute due to the myxedema involvement of the arterial wall. Other potential factors include free water retention due to an inappropriate secretion of anti-diuretic hormone (ADH) and obesity in hypothyroid patients (1,4).

 
Similar to its prevalence in hypothyroidism, hypertension is about 3-fold higher in patients with overt hyperthyroidism compared to normal subjects (1). However, in contrast to hypothyroid patients, the hypertension in hyperthyroidism is primarily “cardiogenic”, where the increased blood pressure levels are mainly maintained by the increased cardiac output due to high stroke volume and heart rate (1).

 
Thus, both hypothyroidism and hyperthyroidism can be associated with hypertension!

 
Bonus pearl: Did you know that hypertension due to hypothyroidism is typically associated with a low-renin state, is particularly sensitive to salt intake, and may not respond as well to angiotensin -converting enzyme inhibitors (1)?

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References
1. Mazza A, Beltramello G, Armigliato M, et al. Arterial hypertension and thyroid disorders: what is important to know in clinical practice? Annales d’Endocrinologie 2011;72:296-303. https://www.sciencedirect.com/science/article/abs/pii/S0003426611000886
2. Dernellis J, Panaretou M. Effects of thyroid replacement therapy on arterial blood pressure in patients with hypertension and hypothyroidism 2002; Am Heart J 2002;143:718-24. https://www.ncbi.nlm.nih.gov/pubmed/11923811
3. Anderson GH, Blakeman N, Steeten DHP. The effect of age on prevalence of secondary forms of hypertension in 4429 consecutively referred patients. J Hypertension 1994;12:609-15. https://insights.ovid.com/hypertension/jhype/1994/05/000/effect-age-prevalence-secondary-forms-hypertension/15/00004872
4. Saito I, ITO K, Saruta T. Hypothyroidism as a cause of hypertension. Hypertension 1983;5:112-15. https://www.ahajournals.org/doi/10.1161/01.hyp.5.1.112
5. Chaker L, Bianco AC, Jonklaas J, et al. Hypothyroidism. Lancet 2017;390:1550-62. https://www.ncbi.nlm.nih.gov/pubmed/28336049

Can hypothyroidism be associated with hypertension?

Despite taking higher doses of warfarin, my patient’s INR won’t budge. What am I missing?

Poor compliance is probably the most common and least “exciting” explanation for low INRs despite seemingly adequate or high warfarin doses.  Otherwise, consider the following: 

Increased vitamin K intake: Since warfarin acts by inhibiting vitamin K recycling by VKORC1 (Vitamin K epOxide Reductase Complex), find out if your patient takes multivitamins or loves foods or products rich in vitamin K, ranging from leafy green vegetables to nutritional supplements( eg, Ensure) and even chewing tobacco!1 

Drug interactions: Warfarin is notorious for interacting with many drugs, although its effect is more often enhanced than counteracted. Run the patient’s med list and look for “counteractors” of warfarin,  including carbamazepine, phenobarbital, phenytoin, rifampin, and dexamethasone.2 

Hypothyroidism: Thyroid hormone seems to be necessary for efficient clearance of the vitamin K-dependent clotting factors (II, VII, IX, and X). Thus, larger doses of warfarin may be needed when patients are hypothyroid.3 

Hyperlipidemia and obesity: High lipid levels may allow for high vitamin K levels (since it’s lipid-soluble and carried in VLDL), especially at the start of therapy.4,5 

What if the INR is falsely low? This is usually not the problem although one major trial took a lot of heat for using a point of care INR device that gave low readings in anemic patients.6  When in doubt, check a chromogenic factor Xa test to confirm; 20-30% activity correlates with a true INR of 2-3.7

If none of these explanations fit the bill, consider genetic testing for warfarin resistance.8,9

Bonus Pearl: Did you know that use of warfarin (introduced in 1948 as a rodenticide) has already led to some selective pressure for VKORC1 mutations in exposed rat populations.10

References

  1. Kuykendall JR, et al. Possible warfarin failure due to interaction with smokeless tobacco. Ann Pharmacother. 2004 Apr;38(4):595-7. https://www.ncbi.nlm.nih.gov/pubmed/14766993
  2. Zhou SF, et al. Substrates, inducers, inhibitors and structure-activity relationships of human Cytochrome P450 2C9 and implications in drug development. Curr Med Chem. 2009;16(27):3480-675. https://www.ncbi.nlm.nih.gov/pubmed/19515014
  3. Bucerius J, et al. Impact of short-term hypothyroidism on systemic anticoagulation in patients with thyroid cancer and coumarin therapy. Thyroid. 2006 Apr;16(4):369-74. https://www.ncbi.nlm.nih.gov/pubmed/16646683
  4. Robinson A, et al. Lipids and warfarin requirements. Thromb Haemost. 1990;63:148–149. https://www.ncbi.nlm.nih.gov/pubmed/16646683
  5. Wallace JL, et al. Comparison of initial warfarin response in obese patients versus non-obese patients. J Thromb Thrombolysis. 2013 Jul;36(1):96-101. https://www.ncbi.nlm.nih.gov/pubmed/23015280
  6. Cohen D. Rivaroxaban: can we trust the evidence? BMJ 2016;352:i575. https://www.bmj.com/content/352/bmj.i575/rapid-responses
  7. Sanfelippo MJ, et al. Use of Chromogenic Assay of Factor X to Accept or Reject INR Results in Warfarin Treated Patients. Clin Med Res. 2009 Sep; 7(3): 103–105. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2757431/
  8. Rost S, et al. Mutations in VKORC1 cause warfarin resistance and multiple coagulation factor deficiency type 2. Nature. 2004;427:537–41. https://www.ncbi.nlm.nih.gov/pubmed/14765194
  9. Schwarz UI, et al. Genetic determinants of response to warfarin during initial anticoagulation. N Engl J Med. 2008 Mar 6;358(10):999-1008. https://www.ncbi.nlm.nih.gov/pubmed/18322281
  10. Rost S, et al. Novel mutations in the VKORC1 gene of wild rats and mice–a response to 50 years of selection pressure by warfarin? BMC Genet. 2009 Feb 6;10:4. https://bmcgenet.biomedcentral.com/articles/10.1186/1471-2156-10-4

Contributed by Nicholas B Bodnar, Harvard Medical School student, Boston, MA.

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Despite taking higher doses of warfarin, my patient’s INR won’t budge. What am I missing?

Why doesn’t excessive ingestion of carrots cause yellow discoloration of the sclera?

Great question! “Carotenoderma” refers to the yellow discoloration of the skin caused by increased serum carotenoids1.  Carotenoids are absorbed by passive diffusion from the gastrointestinal tract which are partially metabolized in the intestinal mucosa and liver to vitamin A, and then transported in the plasma into the intercellular lipids of stratum corneum of the skin which has a high affinity for carotene1,2.

The maximal accumulation of carotenoids occurs in areas with an abundance of sweat glands (eg, the palms, soles, nasolabial folds). In the absence of strateum corneum, the sclera is spared!

Of note, there are many causes of carotenoderma besides excessive ingestion of carrots.  Among foods, increased ingestion of tomatoes, tangerines, red palm oil, and squash may also be responsible1,2

Systemic diseases associated with increase in serum carotenoids (possibly related to decreased conversion to vitamin A, hyperlipidemia, or other factors) include hypothyroidism, diabetes mellitus, anorexia nervosa, nephrotic syndrome, and liver disease.

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References 

  1. Horev L, Ramot Y, Klapholz L. Yellow feet in a patient with breast and thyroid carcinoma, due to oral intake of turmeric. Drug Saf-Case Rep 2015;2:4.https://link.springer.com/article/10.1007/s40800-015-0006-4
  2. Maharshak N, Shapiro J, Trau H. Carotenoderma-a review of the literature. Int J Dermatol 2003;42:178-181. http://onlinelibrary.wiley.com/doi/10.1046/j.1365-4362.2003.01657.x/epdf

 

Contributed by Clara Yang, Medical Student, Harvard Medical School

 

Why doesn’t excessive ingestion of carrots cause yellow discoloration of the sclera?