Diagnosing Myositis and Myopathy: Exam and Testing

Matthew F. Watto, MD; Paul N. Williams, MD


February 01, 2023

This transcript has been edited for clarity.

Matthew F. Watto, MD: Welcome back to The Curbsiders. I'm Dr Matthew Watto, here with my great friend, Dr Paul Nelson Williams. Today we wanted to bring you some quick tips about diagnosing myositis and myopathy.

Paul, this is something that I did not know much about. I knew there was dermatomyositis and polymyositis. But apparently, Paul, there's a lot more. Were you aware of this?

Paul N. Williams, MD: I was in the same boat as you. I knew that I would check a couple labs. If they were abnormal, I would refer to a specialist. But I did not have nearly the framework that I do now after hearing the episode Myositis and Myopathy with Dr Lisa Christopher-Stine.

Watto: There are many subtypes of dermatomyositis, but in general, dermatomyositis holds up as we know it. Multiple clinical and serologic subtypes of polymyositis are now well defined, and they all have different features and prognoses. There is a lot more to it than what I initially thought.

In general, these are autoimmune disorders. They're rare, fortunately. They usually present with muscle weakness and there are extramuscular manifestations. There can be skin features, arthritis, and sometimes these patients have interstitial lung disease. What about some of the other clinical features? Our expert gave us some great pearls about what we should and shouldn't expect from this.

Williams: That's exactly right. She gave some nice, broad definitions and features that I found extraordinarily helpful to frame the discussion, the main point being that the predominant concern in myositis is weakness. You can see isolated weakness, or weakness with mild pain, but myositis doesn't present as an isolated pain syndrome. That is extraordinarily uncommon. If that's what you're seeing, you might be barking up the wrong tree.

Our expert also talked about how to differentiate weakness from fatigue with the "movie theater sign." If you're watching a movie and you are deep in a chair, if suddenly there is a fire, could you get out of the chair without help or would you need someone to physically drag you up? That's a good way to figure out if this is true weakness or fatigue or some combination thereof. I thought that was a really useful way to at least start thinking about and considering myositis.

Watto: Burning or really bad itching of the scalp could be dermatomyositis. She said that's a common feature of the rash and sometimes that's the symptom they complain most about. With the physical exam, this was some stuff that I was totally unaware of. You want to go through that a little bit?

Williams: I can at least go through the things that I have refined after talking to our guest. In terms of the muscle testing specifically, if you are assessing weakness of the neck or the extension and flexion of the hip, you want the patient lying down because otherwise they can recruit other muscle groups. This is a way to isolate those muscle groups. She talked about resisting away from the joints that you're actually testing. For flexion you would have the patient supine, and for extension, you would have them prone.

To test grip strength, typically I have the patient grab my fingers as hard as they can. But Dr Christopher-Stine suggests having them bend their fingers to the first palm crease (rather than making a fist) and then trying to pry them up to test for weakness. That's a much better way of assessing hand strength.

Watto: They can't cheat using the intrinsic muscles of the hand.

There is a lot of lab testing and some of it was surprising. The ANA is often positive, but anemia is not a common finding for some reason in myositis, and inflammatory markers are often normal in dermatomyositis. This was surprising to me because usually I think, Oh, inflammatory markers aren't up; this isn't autoimmune. They seem to be pretty sensitive, and most patients with something autoimmune or inflammation going on have anemia. This doesn't hold to that rule.

If you're thinking dermatomyositis specifically because there's muscle weakness and skin findings, then you have to think about age-appropriate cancer screening. Dr Christopher-Stine said she does an initial CT of the chest, abdomen, and pelvis for pretty much all her patients because they can have cancers or interstitial lung disease. She recommends for middle-aged men getting a PSA screening for prostate cancer, which is not standard practice for all our patients.

We got some really great pearls on this podcast. There's a lot of practical stuff here for us as internists, and we can't cover all of it in this short video. Click on Myositis and Myopathy if you want to hear the full episode. Until next time. I've been Dr Matthew Frank Watto.

Williams: I'm Dr Paul Nelson Williams. Thank you and goodbye.

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