You go into the exam station where you are told that you are in the ER and a gentleman introduces himself as a 35 yo man who started having pain in his left shoulder. He was unable to move the shoulder in an outward and backward directions.

He does not remember any injury to the shoulder. He also does not take any medications. He remembers having a bad sore throat a few weeks ago that he got some Amoxicillin for. He went to his GP after that as he developed a rash from the antibiotic. He does not remember being allergic to penicillin before but now his GP told him that he could not take penicillin anymore.

He travels in the New York subway to work everyday but could not travel that day as he felt unwell and instead came to the Emergency room where he meets you.

He is lying in bed where he was asked to sit - shortly after he walked into the triage room.

The differential diagnoses to be considered should include 1. Supraspinatus tendinitis (because it is common and has pain upon shoulder abduction), 2. Frozen shoulder(as the range of motion is restricted in more than one axis), 3. Splenic rupture (as the patient had an URI that upon receiving Amoxicillin gave the patient a rash - something that happens in patients with Infectious mono and in IM patients have a soft spleen and it can easily rupture and one of the signs of it is pain in the shoulder - particularly when the patient lies down), 4. serum sickness (considering the patient had a reaction to the penicillin), 5. bicipital tendinitis (patients typically complain about pain when they try to flex the shoulder) and 6. acromio-clavicular joint inflammation (as it too can have pain in the joint upon movement of the shoulder in multiple directions). 7. Causes of mono-articular arthritis should be kept in mind too and include - Gonococcus, Septic arthritis, Gout & hemarthrosis.

For the first diagnosis, one should consider asking the following questions: does it hurt to move your shoulder upwards from the side? If the patient shows you just an absolutely diminished range of motion (less than 10 degrees) consider septic arthritis. If on the other hand, the patient can take the arm through a full range of motion without significant impairment, consider a non infective cause.

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