What is the most likely diagnosis for a one‑month history of left shoulder pain (4/10) without swelling, with limited active abduction but relatively preserved passive motion?

Most Likely Diagnosis: Rotator Cuff Tendinopathy (Subacromial Impingement Syndrome)

The clinical presentation of one-month left shoulder pain with limited active abduction but relatively preserved passive motion is most consistent with rotator cuff tendinopathy/subacromial impingement syndrome. This diagnosis is strongly supported by the characteristic pattern of impaired active movement with preserved passive range of motion, which distinguishes rotator cuff pathology from adhesive capsulitis 1.

Key Diagnostic Features Supporting This Diagnosis

Movement Pattern Analysis

• The preservation of passive motion with limited active abduction is pathognomonic for rotator cuff pathology rather than capsular restriction 1, 2
• Limited active abduction specifically indicates subacromial pathology, as the supraspinatus tendon is compressed beneath the coracoacromial arch during this movement 1, 3
• Pain during abduction between 70-120 degrees (the "painful arc") reflects supraspinatus tendon impingement through the narrow subacromial space 1

Age-Specific Considerations

• For patients over 35-40 years, rotator cuff disease and degenerative changes are the predominant pathology, making this the primary diagnostic consideration 1, 2
• The one-month duration classifies this as subacute presentation, consistent with the typical evolution of rotator cuff tendinopathy 1

Critical Differential Diagnosis to Exclude

Adhesive Capsulitis (Frozen Shoulder)

• This diagnosis is effectively ruled out by the preserved passive range of motion 1, 4
• Adhesive capsulitis presents with progressive loss of both active AND passive motion, particularly external rotation and abduction 5, 4
• The positive predictive value for adhesive capsulitis requires passive glenohumeral ROM in abduction <80-90° with corresponding capsular volume <12 mL 4

Hemiplegic Shoulder Pain

• The provided stroke rehabilitation guidelines 5 are not applicable to this clinical scenario unless there is a history of stroke with hemiplegia
• Hemiplegic shoulder pain is associated with motor weakness, shoulder subluxation, and altered movement patterns following stroke 5

Essential Physical Examination Maneuvers

Perform these specific tests to confirm the diagnosis:

• Hawkins' test (forcible internal rotation with arm flexed forward at 90°): 92% sensitive for impingement 1, 6
• Neer's test (passive forward flexion with internal rotation): 88% sensitive for impingement 1, 6
• Empty can test (resisted abduction at 90° with internal rotation): assesses supraspinatus strength 1
• External rotation strength testing: weakness suggests rotator cuff involvement 1
• Assess passive range of motion carefully: preserved passive motion confirms rotator cuff pathology over adhesive capsulitis 1, 3

Recommended Diagnostic Approach

Initial Imaging

• Plain radiographs are the mainstay for initial evaluation (AP, Grashey, axillary, and/or scapular Y projections) to exclude fracture, arthritis, or massive rotator cuff tears 1
• MRI is NOT required at initial presentation when clinical findings clearly establish subacromial impingement 1

When to Obtain Advanced Imaging

• MRI without contrast becomes appropriate only if: 1
  • Symptoms persist despite 3-6 months of adequate conservative therapy
  • Clinical suspicion for full-thickness rotator cuff tear (marked strength loss >2/5)
  • Imaging needed for surgical planning
• Musculoskeletal ultrasound is an excellent alternative with 85% sensitivity and 90% specificity for rotator cuff pathology, equivalent to MRI when performed by experienced operators 1

First-Line Management Strategy

Physical therapy is the most appropriate initial intervention, with evidence showing 80% of patients achieve full recovery within 3-6 months 1.

Conservative Treatment Protocol

• Complete rest from aggravating activities until asymptomatic 5, 1
• Gentle stretching and mobilization techniques, focusing on external rotation and abduction to prevent secondary adhesive capsulitis 5, 1
• Eccentric strengthening exercises once pain-free motion is achieved, specifically recommended for tendinopathy healing 1
• Rotator cuff and scapular stabilizer strengthening as the cornerstone of rehabilitation 5, 1

Adjunctive Measures

• NSAIDs for acute pain management (acetaminophen or ibuprofen if no contraindications) 5
• Subacromial corticosteroid injections for more severe cases when pain is thought related to subacromial bursa or rotator cuff inflammation 5, 1
• Avoid overhead pulley exercises, which encourage uncontrolled abduction and can worsen rotator cuff pathology 1

Common Pitfalls to Avoid

• Do not assume this is adhesive capsulitis without documenting restricted passive motion - this is the most common diagnostic error 1, 4
• Do not order MRI prematurely - imaging is not indicated until after 3-6 months of failed conservative therapy unless there is clinical suspicion for complete tear 1
• Do not overlook scapular dyskinesis during examination, as poor scapular coordination is both cause and effect of rotator cuff pathology 1, 6
• Only 9% of patients with subacromial impingement ultimately require surgical referral after unsuccessful conservative management, so premature orthopedic referral should be avoided 1