This case was reported in a literature article and described the occurrence of Parsonage-Turner syndrome in a 84-year-old male patient who received Influenza vaccine Quadrivalent. On an unknown date, the patient received Influenza vaccine Quadrivalent. On an unknown date, 7 days after receiving Influenza vaccine Quadrivalent, the patient experienced Parsonage-Turner syndrome, axillary nerve injury (serious criteria GSK medically significant), localized muscle weakness, shoulder pain, injected limb mobility decreased, rotator cuff injury and cervical spondylosis. On an unknown date, the outcome of the Parsonage-Turner syndrome, axillary nerve injury, localized muscle weakness, shoulder pain, injected limb mobility decreased, rotator cuff injury and cervical spondylosis were unknown. The reporter considered the Parsonage-Turner syndrome, axillary nerve injury, localized muscle weakness, shoulder pain, injected limb mobility decreased, rotator cuff injury and cervical spondylosis to be related to Influenza vaccine Quadrivalent. Additional information was provided. This case was reported in a literature article and described the occurrence of Parsonage-Turner Syndrome (PTS) in a 84-year-old male patient who was vaccinated with unspecified influenza vaccine (manufacturer unknown). The patient played golf and stayed very active physically. No information on patient's medical or family history or concomitant medication or concurrent condition was provided. On an unspecified date, the patient received injection of unspecified influenza vaccine (flu shot) in the left deltoid (administration route unspecified; dosages unknown; batch number not provided). The age of vaccination was not provided. On an unspecified date, 1 week after the vaccination, the patient described acute onset of shoulder pain and weakness. The patient had done physical therapy for about 3 months without progress. At the age of 85 years, the patient presented with complaints of left shoulder weakness after having had a flu shot in the left deltoid 1 year ago. The patient complained of inability to move his left shoulder above the horizontal plane. The patient was currently taking some herbal medications for pain relief. The patient denied any paresthesias and also any weakness in the distal upper extremity. Physical examination was unremarkable, except for reduced active range of motion of the left shoulder, and 4 out of 5 strength in the left deltoid and left shoulder external rotators. Magnetic resonance imaging (MRI) of the left shoulder showed evidence of an old rotator cuff injury. MRI of the cervical spine showed cervical spondylosis without evidence of nerve or cord impingement. Electromyography of the left upper extremity confirmed the presence of left axillary nerve and suprascapular nerve injury. Treatment was unknown. The outcome of the event was not reported. The authors commended, "We present a case of shoulder weakness due to suprascapular and axillary nerve injury following flu vaccination. Although rare, there are well documented reports of brachial neuritis or Parsonage-Turner syndrome (PTS) following vaccinations. The cause is considered to be a post-infectious reaction or a reaction secondary to a hypersensitivity response. The prognosis for clinical improvement is good, although a number of patients demonstrate residual weakness and atrophy". The authors concluded "Parsonage-Turner syndrome is a rare but distinct disorder with an abrupt onset of shoulder pain, followed by weakness and atrophy of the upper extremity musculature, and a slow recovery requiring months to years. We present a rare case of PTS following influenza vaccination. Clinicians should consider this diagnosis in patients with upper extremity weakness following vaccination."