This medically confirmed literature report (initial receipt 22-Jul-2014) concerns a 66-year-old female patient who had no past medical history. On an unknown date, the patient received Influenza virus vaccine (manufacturer and batch number not provided). On an unknown date, immediately after vaccination (3 hours), the patient developed left arm pain exacerbated by motion. There was a subjective decrease in range of motion. The symptoms included cool, numb, heavy sensation in her left hand, with radiation down the arm, neck, and scapular region. On an unknown date, one day following the vaccination, the patient presented at the clinic for evaluation. Despite intense clinical presentation, physical examination was normal. Her erythrocyte sedimentation rate (ESR) was mildly increased at 43mm/hr. BMI was recorded as 25.7 kg/m2 and CBC was normal. Nine days after presentation, left upper extremity venous duplex ultrasound and MRI cervical spine excluded venous thrombosis and radiculopathy. Degenerative changes were noted on cervical spine MR images. Fluid within subacromial/subdeltoid bursa and physiologic glenohumeral joint fluid was observed on the MRI. It was also noted on the MRI was oblique coronal T2-weighted fat-saturated image of the subacromial/subdeltoid bursal fluid without overlying inflammatory changes [TR/TE: 3,800/60, field of view 14, 4-mm slice thickness within 1-mm inter-slice gap]. The oblique coronal PD image showed equivocal undersurface partial thickness tear of the supraspinatus tendon [TR/TE: 4,000/40, field of view 14, 3-mm slice thickness with 1-mm inter-slice gap]. Thus, it was incidentally noted of low-grade undersurface tears in the posterior margin supraspinatus and anterior margin infraspinatus tendons. The measurement of subcutaneous fat thickness was noted to be 6.6mm on oblique coronal T1-weighted MR images. Laboratory testing did not support any infectious etiology. The patient was not actively anti-coagulated. Her differential diagnosis included- brachial plexus neuropathy and radiculopathy and coincident diagnosis included partial colectomy and osteoarthritis (OA). The patient was treated with NSAIDs and physical therapy. No medical or surgical intervention was initiated. A follow-up exam revealed a normal musculoskeletal exam. The patient had another normal musculoskeletal exam 2.5 years after the event. Outcome was reported as recovered (complete resolution in 30 days). Authors comment: A causal relationship between vaccine administration and deltoid bursitis has been formally established. It has been reported that unintentional injection of vaccine antigen into subacromial/subdeltoid bursa can trigger an inflammatory reaction. Due to variable body habitus and muscle size, the optimum point for vaccine injection may vary among individuals. An improper angle of approach of the needle or increased needle length may result in bursal or cortical penetration, particularly in those with low BMI. Shoulder injury related to vaccine administration presents with persisting and severe shoulder pain may relate to deltoid bursitis, tendonitis, rotator cuff tear, frozen shoulder, impingement syndrome, adhesive capsulitis and shoulder bursitis. Localised intrasubstance oedema like signal in deltoid muscle is most common finding.