Hello everyone, my name is Marla Petrillo. I'm a PGY-3 at MedStar National Rehabilitation Hospital and today I'll be presenting axillary mononeuropathy after the flu shot case report. This was written by myself and Dr. Kat Power, one of our cancer rehabilitation attendings. So I'll start with a little bit of background. So we all know the axillary nerve, that's a big nerve in the shoulder, originates from C5 to 6, runs through the upper trunk and posterior cord of the brachial plexus, then travels down through the quadrilateral space into the axilla, goes behind the humerus, and then ends up innervating the teres minor and deltoid muscles. We most commonly see axillary neuropathy with incorrect axillary crutch use. We can also see it after hemorrhoid fractures and shoulder dislocations due to traction. So in this picture here of the axillary nerve, paying a special attention just in this case to some of the cutaneous branches which actually come superficial on the deltoid, as well as some of the branches that run deep to the deltoid muscle. So our patient is a 25 year old right-handed female, she has no significant past medical history. She presented with severe left shoulder pain and weakness for approximately two months. She developed this pain after she actually received the influenza vaccine as an IM injection into the same arm. Her pain was primarily located over the deltoid or swiss shoulder, abduction, improved with rest, but really significant amount of pain and also some subjective weakness. Her exam was pertinent for some subtle flattening of the left deltoid when compared to the right side. She also had some weakness in the arm. The motor exam was limited because of the pain, but she did have significant weakness, especially with shoulder abduction and shoulder flexion. She underwent a EMG nerve conduction study. The nerve conduction study was non-contributory, however the EMG needle study did show in the left deltoid some increase insertional activity and reduced recruitment. The rest of the study was normal. So this is a really interesting patient. You know, especially in this season, we're all going and getting our flu vaccines, most of which will be placed IM into the deltoid. Plenty of other vaccinations that, you know, we see in the hospital setting. This patient unfortunately had a complication that was consistent with axillary mononeuropathy, causing significant pain and weakness of that shoulder. So it's just important to keep in mind when we're doing these injections that there is the axillary nerve that has branches that run both deep and superficial to the deltoid muscle. In a patient that presents with this constellation of symptoms, it's important to just take a history and make sure they haven't had any injections to this area or other kind of out-of-the-box trauma. Thank you so much for listening. Have a great day.

axillary mononeuropathy

flu shot

axillary nerve

shoulder pain

influenza vaccine