This is an AANEM teachable moment focusing on the use of ultrasound and the workup of patients presenting to the EMG lab with shortness of breath. The case is a 48-year-old man presenting with a six-week history of sudden onset of shortness of breath that came on overnight. It is worse with lying down or when he bends over to tie his shoes. Prior to developing the shortness of breath, he initially developed severe left shoulder pain which was present constantly for about 10 days and then has since resolved. He's referred to the EMG lab after his chest x-ray showed an elevated left hemidiaphragm. Phrenic nerve conduction studies were done using two different recording techniques. One, the electrode is placed here over the diaphragm and the G2 is over the inferior costal margin. The other option is to place G1 over the xiphy sternum with G2 further down, also over the costal margin. And we stimulate the phrenic nerve supraclavicularly and then record from both of these and see which one we get the best response from. So in his case, we got a good response with technique one and this is a typical phrenic C-MAP. The response with technique two wasn't as nice, but on the left side we got no response with either technique. So we then did B-mode ultrasound where we placed the transducer, a linear transducer over the lower costal region, typically starting in the anterior axillary line. So you're trying to look through the ribs at the diaphragm here, deep to the ribs. And it's good to move around until you get the best picture, somewhere in that general vicinity. So on the right, his hemidiaphragm at rest at the end of expiration was nice and normal looking. And you measure it between this pleural covering of the diaphragm and the peritoneal covering of the diaphragm. And then the diaphragm is the dark hypo-echoic area in between those two white lines. And don't be fooled by this intermittent line that sometimes goes across the center of the diaphragm. That's some tendinous fibers that likely go on to become the central tendon. We then took a deep breath in, and his diaphragm thickened significantly, more than doubling in size. So we measured it again between those two hyper-echoic lines. And it was 0.7 centimeters with deep inspiration, which is when the diaphragm contracts. So this gave a thickening fraction of 130%. The left hemidiaphragm was very atrophic. There's this tiny little thin black line here between those two hyper-echoic layers of the peritoneum and the pleura covering the diaphragm. And it was only 0.1 centimeters at rest, and it did not thicken at all when he took a deep breath in. So it had a thickening fraction of 0%. Because of those findings, we did needle EMG of the left diaphragm, and we found two plus fibrillation potentials and only a few complex long-duration motor unit potentials with significantly reduced recruitment, consistent with severe nerve injury. So our final diagnosis was that he had a severe left phrenic neuropathy. And given this clinical scenario, the most likely diagnosis is neuralgic amyotrophy or Parsonage-Turner syndrome. And it is not uncommon for the phrenic nerve to be involved, sometimes in isolation, sometimes bilaterally. So the clinical pearls to take away from this case are that the normal thickness of the diaphragm at rest, which is at the end of expiration, so after a patient has quietly breathed out, you freeze the image and measure it, and it should be greater than about 0.14 centimeters, and that a normal diaphragm should thicken by at least 20% with deep inspiration. The thickening fraction is determined by taking the thickness at end inspiration minus thickness at end expiration, and dividing that by the thickness at end expiration times 100 to give you a percentage. We have published our normal values in this paper, and they were taken from 150 normal subjects of varying age. The other clinical pearl is that the patient should be warned of the risk of severe shortness of breath with immersion in water. Even with a unilateral phrenic neuropathy, where they may not be that symptomatic on land, if a person is to dive into deep water, they can very quickly get into significant distress if they have a unilateral phrenic neuropathy, and we also published this in Neurology in 2020. So a couple of things to take away from this case.

shortness of breath

left shoulder pain

phrenic nerve conduction studies

phrenic neuropathy

diaphragm thickness