A 52-year-old woman with type 2 diabetes mellitus presents 3 weeks after a closed fracture of the proximal humerus treated conservatively with a sling. She reports progressive swelling of the shoulder, stiffness, and severe pain disproportionate to the fracture severity. On examination, the shoulder is swollen, warm, and tender. Active and passive range of motion are severely restricted in all planes. X-ray shows no displacement of the fracture. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Complex Regional Pain Syndrome (CRPS Type 1) ### Key Diagnostic Features Present **High-Yield:** CRPS Type 1 (formerly reflex sympathetic dystrophy) is a post-traumatic pain syndrome that develops after fracture or soft tissue injury WITHOUT confirmed nerve injury. ### Budapest Criteria for CRPS Diagnosis The patient meets diagnostic criteria: | Criterion | Present in Case | Details | |-----------|-----------------|----------| | **Initiating event** | Yes | Proximal humerus fracture | | **Continuous pain** | Yes | Progressive pain 3 weeks post-injury | | **Pain disproportionate to injury** | Yes | Severe pain despite stable fracture | | **Edema** | Yes | Progressive shoulder swelling | | **Skin changes** | Implied | Swelling, warmth | | **Motor dysfunction** | Yes | Severe restriction of ROM | | **Symptoms in multiple body regions** | Yes | Shoulder involvement | | **Temporal progression** | Yes | Worsening over 3 weeks | **Key Point:** CRPS Type 1 occurs WITHOUT documented nerve injury; CRPS Type 2 occurs AFTER confirmed nerve injury. ### Why This Patient Is High-Risk **Mnemonic: DIABETES** — Risk factors for CRPS: - **D**iabetes mellitus ✓ (present in this case) - **I**mmobilization (sling use) ✓ - **A**ge >50 years ✓ - **B**one fracture ✓ - **E**arly aggressive rehabilitation (sometimes) - **T**rauma severity - **E**xcessive pain - **S**tress ### Pathophysiology ```mermaid flowchart TD A[Fracture/Trauma]:::outcome --> B[Inflammatory cascade + neurogenic inflammation]:::action B --> C[Sympathetic nervous system sensitization]:::action C --> D[Peripheral and central sensitization]:::action D --> E[Persistent pain disproportionate to injury]:::outcome E --> F[Edema, vasomotor changes, motor dysfunction]:::outcome F --> G[CRPS Type 1]:::outcome ``` **Clinical Pearl:** The hallmark is **pain out of proportion** combined with **multi-system involvement** (sensory, motor, autonomic, trophic changes). Early recognition and aggressive physiotherapy are crucial to prevent chronicity. ### Distinguishing Features | Feature | CRPS Type 1 | Adhesive Capsulitis | Septic Arthritis | AVN | |---------|------------|-------------------|-----------------|-----| | **Onset** | Days to weeks | Weeks to months | Acute (days) | Months to years | | **Pain severity** | Severe, disproportionate | Moderate, proportionate | Severe + fever | Progressive | | **Swelling** | Yes, edema | Minimal | Yes + effusion | No early swelling | | **Warmth** | Yes (vasomotor) | No | Yes (infection) | No | | **ROM restriction** | All planes | Capsular pattern | All planes | Gradually progressive | | **Systemic signs** | No | No | Yes (fever, WBC↑) | No | | **Imaging** | Normal/osteopenia | Normal | Effusion, joint space loss | Subchondral lucency | **Warning:** Do NOT confuse adhesive capsulitis (frozen shoulder), which develops insidiously over months with gradual ROM loss. CRPS is acute-onset with severe pain and multi-system signs within weeks. ## Why Other Options Are Incorrect **Adhesive capsulitis** typically develops over months (not 3 weeks) with gradual, progressive stiffness and pain proportionate to the condition. There is no vasomotor instability (warmth, swelling) or disproportionate pain. **Septic arthritis** would present with fever, elevated WBC, joint effusion on imaging, and positive cultures. The shoulder is not acutely infected; the fracture is stable and uncomplicated. **Avascular necrosis** develops months to years after injury (especially with femoral neck or proximal humerus fractures). At 3 weeks, the patient would not yet show radiographic evidence, and the presentation would be different (progressive loss of ROM without acute vasomotor signs).