Case Report31-year-old female patient, with a history of hypothyroidism in treatment with levothyroxine 75 mg per day, who consults for 8 days of disabling pain in her left shoulder of dorsal predominance, with irradiation to the triceps region, limiting the shoulder abduction and elbow extension, and no other symptoms.At the admission, her vital signs are interpreted as normal, and it is evident that the pain has a distribution in dermatome C5 and C6, reflex alteration in the involved limb not documented and also no loss of muscular force.Shoulder ultrasound is performed reporting free liquid in periarticular region, so simple magnetic resonance imaging in her left shoulder is carried out resulting in an increase in the signal intensity in the fluid-sensitive sequences of the supraspinous muscle and deltoids, especially in her lateral belly, findings compatible with brachial neuritis (Parsonage-Turner syndrome) (Figure 1).Subsequently, an electromyography