What could be the diagnosis for severe pain when moving my arm across my chest or behind my back?

Shoulder Impingement Syndrome or Rotator Cuff Tendinopathy

The most likely diagnosis is shoulder impingement syndrome or rotator cuff-related shoulder pain (RCRSP), which characteristically causes severe pain with cross-body adduction (arm across chest) and internal rotation (arm behind back) movements. 1

Key Diagnostic Features

Pain with specific movements is pathognomonic for rotator cuff disorders:

• Cross-body adduction test (moving arm across anterior chest) reproduces pain in subacromial impingement and acromioclavicular joint pathology 1
• Internal rotation behind back (reaching behind to touch opposite shoulder blade) stresses the rotator cuff tendons and subacromial space 2
• Overhead activities typically worsen symptoms in rotator cuff tendinopathy 1

Clinical Examination Findings to Confirm Diagnosis

The following examination maneuvers help establish the diagnosis:

• Empty can test (resisted abduction at 90 degrees with thumbs down) demonstrates weakness and pain in supraspinatus tendinopathy 1
• External rotation weakness against resistance suggests infraspinatus/teres minor involvement 1
• Positive impingement sign (pain with passive forward flexion to 180 degrees) indicates subacromial impingement 1, 3
• Painful arc between 60-120 degrees of abduction is characteristic 2

Differential Diagnosis to Consider

Acromioclavicular (AC) joint osteoarthritis presents similarly but has distinct features:

• Superior shoulder pain with point tenderness directly over AC joint 1
• Positive cross-body adduction test (your primary symptom) 1
• Pain localized to the top of the shoulder rather than lateral deltoid region 1

Adhesive capsulitis (frozen shoulder) must be excluded:

• Presents with diffuse shoulder pain and restricted passive range of motion in all planes 1
• Associated with diabetes and thyroid disorders 1
• If passive motion is preserved, adhesive capsulitis is unlikely 1

Critical Red Flags Requiring Urgent Evaluation

While musculoskeletal causes are most likely, immediately exclude cardiac causes if:

• Pain radiates to jaw, neck, or left arm with associated diaphoresis, nausea, or dyspnea 4, 5
• Patient has cardiovascular risk factors (diabetes, hypertension, age >50 years) 4
• Pain occurs at rest or with minimal exertion 4
• Positional chest pain is usually nonischemic, but cardiac causes must still be excluded in high-risk patients 4

Diagnostic Algorithm

Follow this systematic approach:

1. Reproduce the pain with cross-body adduction and internal rotation maneuvers to confirm shoulder origin 1

2. Assess active versus passive range of motion - if passive motion is restricted equally, consider adhesive capsulitis; if only active motion is limited, rotator cuff pathology is more likely 1

3. Perform rotator cuff strength testing - weakness on empty can test and external rotation suggests rotator cuff tear rather than simple tendinopathy 1

4. Palpate for point tenderness - AC joint tenderness suggests AC arthritis; lateral shoulder tenderness suggests rotator cuff/subacromial pathology 1

5. Order plain radiographs initially to evaluate for AC joint arthritis, calcific tendinitis, or massive rotator cuff tears with superior humeral head migration 1

6. Obtain MRI or ultrasound if diagnosis remains unclear or if rotator cuff tear is suspected based on weakness and positive clinical tests 1

Common Pitfalls to Avoid

Do not assume all shoulder pain is musculoskeletal:

• Women, elderly patients (>75 years), and diabetics frequently present with atypical cardiac symptoms including shoulder or upper extremity pain 4, 5
• Obtain ECG and cardiac troponin if any concern for acute coronary syndrome 5

Do not rely on single clinical tests:

• A clinical decision rule combining pain with overhead activity + weakness on empty can test + weakness on external rotation + positive impingement sign provides the highest diagnostic accuracy for rotator cuff tears 1

Do not overlook referred pain:

• Cervical spine disorders commonly refer pain to the shoulder region 6
• Postural problems can cause shoulder pain 6