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Hyperthyroidism - 8/15/2012

posted Aug 15, 2012, 2:06 PM by Rohit Das   [ updated Dec 27, 2012, 7:11 AM by Purnema Madahar ]

This week has so far been pretty heavy on quality Endocrine learning, and today was no exception. Chief of Service with Dr. Surks today was dedicated to hyperthyroidism, specifically around a patient admitted with 3-4 months of weight loss, increased appetite who was ultimately diagnosed with Grave’s Disease. So let’s talk about when the thyroid works too much and breaks duty hour regulations…  

  • Hyperthyroidism is not a terribly common illness – it has a prevalence of 1.3%, and is much more common in women as compared to men (about a 5:1 ratio). The prevalence increases to 4-5% in elderly women.         
  • Of the potential etiologies, Grave’s Disease is by far the most common (pre-test probabilities people…), and represents 50-80% of presenting cases. There are several other much less common causes – on the attached 2008 review article, Table 2 provides a nice review. 
  • Can we use history and physical to accurately diagnose hyperthyroidism? Absolutely. Eyelid retraction (+LR of 30), lid lag (+LR of ~20), and fine finger tremor (+LR ~10) are particular powerful POSITIVE signs. The absence of a pulse > 90 (-LR of 0.2), an enlarged thyroid (-LR of 0.1), and fine finger tremor (-LR of 0.3) are particularly powerful NEGATIVE signs.         
  • The Wayne Index (attached), which is like 50 years old, is also a very handy tool. Scoring ≥ 20 points has a +LR of around 20, and scoring < 11 points has a +LR of 0.04 – both also very powerful…       
  • Geriatric hyperthyroidism is a bit of a different disease, and the above clinical tools may not be as useful. In particular, they have less tachycardia and goiter than younger patients. More specifically, in one study, up to one-third of elderly patients with hyperthyroidism had a Wayne Index score of < 11.

Once we diagnose hyperthyroidism via the above clinical tools and then subsequent thyroid function studies, it is then important to determine the etiology. This is where a radioactive iodine uptake scan comes in:       

  • HIGH uptake scans indicate synthesis of hormone, and are consistent with Grave’s (diffuse uptake), and toxic adenoma/multinodular goiter (more localized uptake); in Grave’s disease, anti-thyroglobulin antibodies are also helpful, if positive.      
  • LOW uptake scans represent destruction of thyroid tissue with release of hormone, and consistent with thyroiditis (as Dr. Surks mentioned, probably more common than we think, as the majority is probably subclinical), amiodarone toxicity, radiation, etc. Of note, iodine loads for contrast procedures may lead to a falsely negative scan as well…

So what do we do for these patients? Well, it differs a bit dependent on the etiology, but let’s focus on Grave’s:         

  • B-blockers provide symptomatic relief, allow patients to tolerate hyperthyroidism better, and also mildly decrease T4 to T3 conversion peripherally.       
  •  Methimazole, the most commonly used anti-thyroid medication, is effective in making patients euthyroid after 4-8 weeks of therapy. Though 20-30% of patients in the U.S obtain long-term remission, the majority relapse, and ultimately require definitive therapy…which brings us to…  
  • Radioactive Iodine…there are two approaches to RAI – treat with enough iodine to make a patient euthyroid, or aim to destroy the gland completely, ultimately leading to a hypothyroid state. Though the former avoids long-term thyroxine supplementation, most of these patients will require repeated doses due to persistent subclinical or overt hyperthyroidism. Even in patients who get an ablative dose, 10-20% may need subsequent dosing (usually in patients with more severe disease).       
  • Surgery is also an option for patients with Grave’s, but generally reserved for patients with more unique situations – large goiters, patients who wish for definitive therapy, patients who do want RAI, and most importantly, patients who have a coexisting suspicious nodule.

A quick blurb on an important hyperthyroid related inpatient issue – thyroid storm (review article attached). Though relatively rare, it is life-threatening, and carries a significant mortality (10-15%)       

  • The most common etiology is again, Grave’s Disease, but usually there is some associated precipitating, stress-inducing factor – surgery, infection, trauma, giving birth are some common scenarios.         
  • Diagnosis is clinical, and Table 1 of the attached review article provides one of the more commonly used diagnostic criteria scheme. Generally speaking, the symptoms are mainly a marked exacerbation of general hyperthyroid symptoms.       
  • Treatment is multimodal, with a step by step approach, involving B-blockers, agents to block synthesis of hormones, iodine to prevent release of hormone, and finally systemic steroids – well, because, steroids make everyone feel better.

So, I think we’ve covered hyperthyroid and their para-friends well this week. Please make sure to at least read the review articles to drive the key clinical points home! Until tomorrow!

                                                                                                                                           

Grave's Disease
Brent, NEJM 2008 Volume 358: 2594-605

Nayak et. al., Endocrin Metab Clin Am 2006, Volume 35: 663-686

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