What is the differential diagnosis and treatment approach for a patient presenting with shoulder pain?

Differential Diagnosis of Shoulder Pain

The differential diagnosis of shoulder pain should be systematically approached based on patient age, mechanism of injury, and anatomical structures involved, with radiography as the initial imaging modality for all presentations. 1

Primary Differential Diagnoses by Age and Presentation

Traumatic Presentations

• Fractures: Proximal humerus, clavicle, or scapular fractures—evaluate with standard radiographic series including AP, Grashey, and axillary or scapular Y views 1
• Glenohumeral dislocation/instability: Most common in younger patients, requires orthogonal radiographic views to confirm; look for Hill-Sachs deformity or bony Bankart lesions 1
• Acromioclavicular joint injury: Assess with dedicated AC joint views 1

Age-Stratified Soft Tissue Pathology

• Patients <35 years: Labral tears and instability predominate—suspect when history includes recurrent subluxation, "dead arm" sensation, or mechanical symptoms 1
• Patients ≥35 years: Rotator cuff disease becomes the primary concern—look for pain with overhead activities, night pain, weakness with external rotation or abduction 1
• Biceps tendon pathology: Pain in anterior shoulder, positive Speed's or Yergason's test 1

Inflammatory/Infectious Causes

• Septic arthritis: Fever, acute onset, severe pain with any motion, elevated inflammatory markers—requires urgent arthrocentesis 1
• Osteomyelitis: Consider in immunocompromised patients or those with recent bacteremia 1

Neurologic Causes

• Cervical radiculopathy: Pain radiating from neck, dermatomal sensory changes, weakness in myotomal distribution—requires cervical spine imaging 2
• Parsonage-Turner syndrome: Acute severe shoulder pain followed by weakness, often bilateral, no musculoskeletal inflammation 3
• Suprascapular nerve entrapment: Posterior shoulder pain, infraspinatus/supraspinatus atrophy 1

Referred Pain (Critical "Red Flags")

• Pulmonary pathology: Pancoast tumor, pneumonia, pulmonary embolism—look for dyspnea, cough, fever, smoking history 4
• Cardiac ischemia: Left shoulder pain with exertional component, associated chest discomfort, cardiac risk factors 4
• Intra-abdominal pathology: Diaphragmatic irritation from cholecystitis, splenic injury, or subphrenic abscess 4, 5
• Neoplasm: Unremitting pain, night pain unrelieved by rest, constitutional symptoms, history of malignancy 1

Diagnostic Approach Algorithm

Initial Evaluation

1. Obtain radiographs first for ALL patients: Minimum 3 views including AP, Grashey, and axillary or scapular Y projections 1
2. Identify red flags requiring urgent referral: Fever with joint effusion, acute neurologic deficits, suspected cardiac/pulmonary pathology, or constitutional symptoms 1, 4

If Radiographs Show Fracture

• Order CT without contrast to characterize fracture complexity, displacement, and surgical planning 1
• Consider MRI without contrast only if assessing concurrent rotator cuff injury in patients not planned for surgical fixation 1

If Radiographs Negative or Indeterminate

For suspected instability/dislocation:

• MRI without IV contrast is the primary study—post-traumatic effusion provides natural arthrography 1
• CT without contrast may be appropriate when bone loss assessment is critical 1

For suspected labral tear:

• Age <35 years: MR arthrography is reference standard in subacute/chronic settings when joint effusion has resolved 1
• Acute trauma: MRI without contrast preferred due to hemarthrosis providing joint distention 1
• CT arthrography if MRI contraindicated 1

For suspected rotator cuff tear:

• MRI without contrast OR ultrasound are equivalent first-line studies—choice depends on local expertise 1
• MRI preferred when: large body habitus, restricted range of motion, or suspicion of concurrent labral pathology 1
• Ultrasound operator-dependent and limited for deep structures and marrow evaluation 1

For suspected septic arthritis:

• Ultrasound-guided or fluoroscopy-guided arthrocentesis is the procedure of choice—imaging is for guidance, not diagnosis 1
• MRI with and without contrast may be appropriate if clinical concern warrants after aspiration 1

If Cervical Spine Involvement Suspected

• Obtain cervical spine radiographs initially 2
• MRI cervical and thoracic spine when radiographs noncontributory or nerve root compression suspected 2

Treatment Approach by Diagnosis

Conservative Management (First-Line for Most Non-Urgent Pathology)

• NSAIDs: Ibuprofen 400-800 mg three to four times daily as first-line pharmacologic treatment 2
• Structured exercise program: Cervical/thoracic mobility, shoulder girdle strengthening, postural correction 2
• Patient education: Positioning, ergonomics, activity modification—particularly important before discharge 1, 2
• Avoid overhead pulley exercises—these can exacerbate shoulder pain 1, 2

Neuropathic Pain Component

• Neuromodulating medications (gabapentin, pregabalin) when sensory changes, allodynia, or hyperpathia present 1, 2

Interventional Options After Failed Conservative Management

• Suprascapular nerve blocks: Effective for persistent shoulder pain unresponsive to conservative measures 1, 2
• Botulinum toxin injections: Useful for severe hypertonicity or spasticity-related pain 1, 2
• Corticosteroid injections (glenohumeral or subacromial): Limited evidence, consider for localized inflammation 1, 2

Surgical Referral Indications

• Acute fractures requiring fixation 1
• Failed adequate conservative management (typically ≥3 months) 2, 6
• Progressive neurological deficits 2
• Severe restrictions in range of motion with muscle contractures 1

Critical Pitfalls to Avoid

• Do not assume imaging findings correlate with symptoms—cervical spondylosis and rotator cuff changes are common in asymptomatic individuals 2
• Do not miss referred pain sources—always assess for pulmonary, cardiac, and abdominal pathology when presentation atypical 4, 5
• Do not order MRI before radiographs—radiography must be the initial screening modality 1
• Do not use transthoracic views—these offer little diagnostic value 1
• Limit opioid use—risks outweigh benefits for chronic shoulder pain management 2
• Do not delay arthrocentesis when septic arthritis suspected—this is a surgical emergency 1