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Hypothyrodism and Musculoskeletal Issues - 9/26/2012

posted Sep 26, 2012, 6:46 AM by Rohit Das   [ updated Dec 27, 2012, 6:48 AM by Purnema Madahar ]

I’m backkkkkkk…today’s topic centered on a presentation of hypothyroidism. This is an extremely extensive topic, and mostly an outpatient issue, so I’ll focus on some aspects of this very common disease.

Hypothyroidism is a common phenomenon, occurring in up to 2% of the general population. Subclinical hypothyroidism, defined as normal free T4 with a high TSH (either with mild symptoms or asymptomatic) is even more common, seen in 5-10% of patients (and progresses to overt hypothyroidism at a rate of about 5% per year). This number gets even higher in elderly woman. Hypothyroidism is also much more common in women, 5-8 fold to be specific.

  • Hypothyroidism can have a very variable presentation, ranging from completely asymptomatic to myxedema coma in the appropriate setting. There are some particularly predictive findings to make the blood tests we send more accurate…specifically:
  • Cool, dry, or coarse skin has a +LR of 3-4. Hypothyroid speech (characterized as slow rate/rhythm, low-pitched and nasal, as if the patient had a cold) is also very predictive, with a +LR of ~5. Bradycardia has a +LR of ~4. Finally, delayed ankle reflexes is also helpful, with a +LR of around 3-4.
  • The most common cause of hypothyroidism, by far, is chronic autoimmune (i.e., Hashimoto’s) thyroiditis, which represents 60-70% of cases. Another common causes is us, via surgery, radiation or radioiodine treatment. Certain drugs can also cause hypothyroidism, including amiodarone and lithium.
  • Treatment, for the most part, is simple – T4 replacement at a dose of 1.6 mcg/kg/day. Though, the required dose can vary from 50-200 mcg/day; patients with Hashimoto’s generally need less replacement as compared to those who have an iatrogenic etiology.

Now – a word of thyroid-related muscle manifestations. The patient presented today had classic symptoms for hypothyroidism, and also came into the hospital with a CPK of around 3000.

  • Muscle involvement and muscle related complaints are extremely common in hypothyroidism. In one series, nearly 80% of patients had neuromuscular complaints, and of those patients, almost 40% had clinical weakness on manual muscle strength testing. Not surprisingly, patients with overt/severe hypothyroidism had more significant muscular symptoms.
  • Importantly, CPK elevation in patients with overt hypothyroidism is the norm, occurring in more than 50% of patients (but usually <10-times the upper limit of normal). It also occurs in 10% of patients with subclinical hypothyroidism. There is no clear correlation with CPK levels and neuromuscular symptoms, but the data does suggest a correlation between CPK and TSH. CPK elevations also commonly occur BEFORE the clinical manifestations of hypothyroidism take over.
  • On the more severe end of the spectrum, hypothyroidism does have seem weak causal associations with a proximal myopathy presentation (similar to polymyositis) and rhabdomyolysis (usually still in the context of some trigger – vigorous exercise or statin use, for example).
  • ….All of this serves to reinforce a couple of things – hypothyroidism has a wide presenting spectrum for every organ system it effects, and secondly, for any patient presenting with muscular issues – check their TSH.

I’ve attached some review articles pertaining to the above topics, as usual.

…This will be my last daily of the month (wipe away those tears…), as I’ll be moving to Weiler later this week. I’ll to try to keep this going during in October, but the interview season will inevitably make it inconsistent. I hope you guys are learning from the daily and it has motivated at least some of you to get your reading in and solidify your fund of knowledge. A sincere thanks to those who have expressed their appreciation thus far. Until next time…KEEP ON READING!

Chronic Autoimmume Thyroiditis
Dayan et. al., NEJM 1996, Volume 335 (2): 99-107

Scott et. al., Muscle & Nerve 2002, Volume 26: 141-144

Heklmosy et. al., Endocrine Res. 2005, Volume 31 (3): 171-175
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