Swelling ECRB and ECRL muscle

[Xue Heng]

Hi, Steve!
I’m sorry that I come again.
This is a 25-year-old female, complaining forearm swelling for about 2 years.
She had no history of trauma and she was not an athlete.
She felt soreness of the same place sometimes when she playing badminton, but the soreness was not severe.
US findings included swelling of ECRB and ECRL muscle in the forearm, without increased blood signal.
I just wondered whether the hypoechoic or hyperechoic region was abnormal.
And what was the pathological process of this finding?
Thank you, Steve.

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[Stephen Bird]

Hi Xue,

Nice images,

I think they are normal.
The hypo echoic and hyper echoic area is from anisotropy and if you rock the probe a little I think the hypo echoic area will become more echogenic and the echogenic area will simultaneously become hypoechoc.

This looks like a strong, healthy muscle and they are very anisotropic when they are like this.
You say she is not an athlete but that muscle looks stronger than mine and yours!
I bet she would beat you easily at badminton.
Sometimes you can get pain with overuse as part of a delayed onset muscle soreness scenario (DOMS) and if it is bad enough it can progress to rhabdomyolysis. But I don’t see any changes suggestive of this. I would expect the muscle to be more echogenic if this was the case.
These muscles are innervated by the posterior interosseous nerve (PIN). You have shown the PIN beautiful in your video and you can see it entering the supinator at the arcade of Frohse. The PIN is fairly big in size but this can be normal.
I would so a resisted supination test and look for compression of the PIN at the arcade of Frohse.
It is possible this is the cause of the pain (radial tunnel syndrome). It is not a common diagnosis in my experience but worth considering.
What was the comparison with the other side like?
It may be the muscles are bigger as it is the dominant arm and badminton uses such a lot of forearm strength.

Did the muscle feel firm clinically compared to the other side?

Steve

[Xue Heng]

Hi, Steve! Thank you again for your meticulous answer.
Yes, it seems anisotropy is the most probable reason for this phenomenon.
I did not consider the possibility of radial tunnel syndrome, but I just inadvertently scanned the PIN entering the supinator at the arcade of Frohse.
I’m sorry I did not compare the echo of the muscle to the other side.
And I guess the affected muscle did not feel firm clinically compared to the other side.
Thank you, Steve. I admit anisotropy is everywhere in MSK ultrasound.
I know it is most obvious in tendon and ligament, but I’m unaware of the fact that it could affect the echo of muscle as well.

[Stephen Bird]

Indeed, anisotropy is everywhere,

You see it is tendons, ligaments, nerves and indeed in muscle.

You even see it in paediatric kidneys and other organs as well.

Nice work Xue.

Steve

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