690 - Post-Influenza Vaccination Subacromial Bursitis in a Patient with Chronic Rotator Cuff Tendinosis: A Case Report

Case Diagnosis: Subacromial Bursitis Induced by Improper Influenza Vaccination Technique in a Patient with Chronic Rotator Cuff Tendinosis

Case Description: A 43-year-old female with a history of repetitive right shoulder dislocations and rotator cuff tendinopathy developed severe right shoulder pain and restricted motion following influenza vaccination. She reported the injection was administered high on the deltoid. The pain was localized to the right shoulder, exacerbated by overhead activities, and refractory to NSAIDs and physical therapy. Physical examination revealed subacromial tenderness and a positive Hawkins-Kennedy test. Point-of-care ultrasound confirmed subacromial bursitis without evidence of rotator cuff tear, prompting treatment with ultrasound-guided subacromial bursal corticosteroid injection via a lateral approach. The treatment resulted in immediate pain reduction. One-month follow-up demonstrated resolution of symptoms and full return to activities without limitations.

Discussions: Subacromial bursitis is an uncommon adverse effect following vaccination, with few cases reported in the literature. The pathophysiology may involve an excessive immune-mediated inflammatory response compounded by mechanical injury from improper injection technique. In this case, the vaccine injection may have been administered too superiorly and deeply, compromising the subacromial space and reaching the inferolaterally extending bursa. Risk factors for shoulder injuries related to vaccine administration (SIRVA) include female gender, minimal deltoid muscle mass, and prior shoulder injury. Physiatrists should maintain a broad differential when evaluating acute on chronic shoulder pain and take relevant history regarding recent vaccinations. Individuals at higher risk for SIRVA may benefit from additional counseling and closer follow-up post-vaccination. Future research could determine if existing rotator cuff tendinopathy increases risk of subacromial bursitis following vaccination.

Conclusions: This case highlights subacromial bursitis as a potential complication of influenza vaccination, emphasizing the importance of proper technique to prevent SIRVA and the effectiveness of ultrasound-guided steroid injections. Physiatrists should include SIRVA in the differential when evaluating worsening shoulder pain in patients with pre-existing shoulder conditions.