Tasty Morsels of EM 044 – Thyrotoxicosis Factitia

18 Jan

As always, this is from the ever expanding google doc on bits and bobs I read and learn from and transfer here for all our learning pleasure.

This was something I wasn’t even aware existed but worth considering.

Classic symptoms of hyperthyroidism

  • tachycardia
    • usually sinus
    • a fib common too
  • sweating/feeling warm
  • poor sleep
  • weight loss
  • possible fine tremor
  • eye signs (Graves only)

Causes of these symptoms

  • usually Graves disease in the west
  • toxic multinodular goitre in areas of iodine deficiency
  • thyroiditis
  • the odd tumour here and there
  • the odd drug here and there (amiodarone and lithium being the big ones)
  • exogenous thyroid hormone use (rejoicing in the name thyrotoxicosis factitia)

The (very) basic physiology

  • Thyroid Stimulating Hormone (TSH) causes thyroid to produce more thyroid hormones
    • controlled by the axis of evil, hypothalamic-pituitary-thyroid axis
  • The hormones are:
    • T3 (triiodo- thyronine)
    • T4 (thyroxine)
  • Most T3 comes from conversion of T4 to T3 peripherally (liver and muscle mainly)
  • T3 is more biologically active
  • In most hospitals I’ve worked T3 isn’t measured routinely

Thyroid hormones can be taken surreptitiously in a few situations

  • reported outbreaks of hamburger thyrotoxicosis from ground beef from the neck of the animal
  • ingestion of various weight loss products that can contain either T3 or T4
    • note if it’s T3 causing the symptoms then T4 may be normal but the TSH should be suppressed. If your lab doesn’t normally measure T3 then it’s worth thinking about (a very smart biochemist had to explain all this to me)

The differentiating feature is probably the eye signs. Graves is the commonest cause of thyrotoxicosis in the west so if you see someone with classic hyperthyroidism and no eye signs then it’s always worth asking them about various supplements they may be taking.

References:

  • Rosens 8th Chap 128
  • UpToDate: Exogenous hyperthyroidism
    • An outbreak of thyrotoxicosis caused by the consumption of bovine thyroid gland in ground beef. Hedberg CW, N Engl J Med. 1987;316(16):993.

 

 

 

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