Atypical progress of frozen shoulder after COVID-19 vaccination: A case report

BACKGROUND: After vaccination was mandated worldwide, various adverse effects associated with the coronavirus disease 2019 (COVID-19) vaccination, including shoulder pain, have been reported. Here, we report a case of new-onset shoulder pain after BNT162b2 (Comirnaty, Pfizer-BioNTech) mRNA vaccination. CASE SUMMARY: A 50-year-old man visited our rehabilitation center with left shoulder range of motion (ROM) limitation that had persisted for more than 5 mo. The history included no specific noteworthy events, except vaccination. The pain in the patient’s left deltoid muscle appeared 1 day after the second BNT162b2 vaccination and intensified to severe pain. The patient self-administered aspirin, with which the pain subsided immediately, whereas ROM limitation persisted. At the first visit, the patient complained of dull pain and ROM restriction of the left shoulder (flexion 130°, abduction 110°, and external rotation 40°). Among the diagnostic studies conducted for the evaluation of the shoulder, magnetic resonance imaging showed a thickened coracohumeral ligament. Nerve conduction studies and needle electromyography showed no electrodiagnostic abnormalities. The patient received comprehensive rehabilitation for 7 mo and had an overall improvement in pain and ROM of the left shoulder. CONCLUSION: In this case of severe shoulder pain after COVID-19 vaccination that subsided immediately with aspirin treatment, the exact cause and mechanism of pain are unclear. However, the clinical symptoms and diagnostic workups in our report suggest the possibility that the COVID-19 vaccination triggered an immunochemical response that resulted in shoulder pathology.