Disclosures: Marla A. Petriello, DO: No financial relationships or conflicts of interest

Case Description: The patient presented with two months of severe left shoulder pain and weakness immediately following receipt of the intra-muscular influenza vaccine in the same arm. The pain was primarily located over the deltoid. The pain was worse with shoulder abduction and improved with rest. The patient reported weakness primarily in shoulder abduction.

Setting: Outpatient physiatry clinic

Patient: 25 year old right handed female with no significant past medical history Assessment/

Results: On physical exam of the left arm, there was noted subtle flattening of the left deltoid compared to the right. Strength was 3/5 shoulder abduction, elbow flexion 4/5, elbow extension 4/5, wrist extensors 4/5, grip 5/5. Motor exam was limited by pain. Sensation to light touch was intact throughout the left upper extremity. EMG/NCS evaluation was completed. NCS testing was unrevealing. EMG needle evaluation of the left deltoid showed decreased insertional activity and reduced recruitment, and all remaining muscles showed no evidence of electrical instability. These findings were consistent with left axillary nerve mononeuropathy.

Discussion: This patient presented with severe left shoulder pain and associated weakness after receiving the influenza vaccine in the same arm. History, physical exam, and EMG findings indicated a diagnosis of left axillary nerve mononeuropathy, with the less likely possibility is an acute brachial neuritis isolated to the axillary nerve. Due to the anatomy of the axillary nerve with branches both superficial and deep to the deltoid muscle, it is likely that the injury occurred during the intramuscular injection of the influenza vaccine.

Conclusion: This case demonstrates the possible risk of direct axillary nerve injury with intramuscular injection into the deltoid.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/axillary-mononeuropathy-after-the-flu-shot-a-case-report/