Complex Regional Pain Syndrome (CRPS) is a chronic pain condition that most often affects a single limb, usually after an injury. It is characterized by pain that is out of proportion to the severity of the initial injury and is often accompanied by autonomic, sensory, motor, and trophic changes. Understanding the transition from an acute injury to the chronic, centralized state of CRPS is vital for effective interventional and rehabilitative planning.

1. Classification and Etiology

CRPS is traditionally divided into two types based on the presence of an identifiable nerve injury:

• CRPS Type I (formerly Reflex Sympathetic Dystrophy): Develops after a noxious event or immobilization (e.g., a simple fracture, sprain, or even surgery) without a documented lesion to a major nerve.
• CRPS Type II (formerly Causalgia): Develops after a confirmed injury to a major peripheral nerve (e.g., a crush injury to the tibial nerve).

2. Pathophysiology: A Multi-Mechanism Disorder

The pathogenesis of CRPS is not fully understood but involves a combination of peripheral and central processes:

• Neurogenic Inflammation: After an injury, there is an excessive release of pro-inflammatory neuropeptides (such as Substance P and Calcitonin Gene-Related Peptide) from peripheral nerve endings. This leads to the classic “warm” phase of CRPS, characterized by vasodilation, edema, and redness.
• Sympathetic Nervous System Dysfunction: The “sympathetically maintained pain” (SMP) theory suggests an abnormal coupling between the sympathetic and nociceptive systems. This can manifest as altered skin temperature, sweating (sudomotor changes), and color changes.
• Central Sensitization: Persistent nociceptive input leads to increased excitability of dorsal horn neurons. This manifests clinically as allodynia (pain from a non-painful stimulus) and hyperalgesia (increased pain from a painful stimulus).
• Cortical Reorganization: Functional MRI studies have shown that the representation of the affected limb in the primary somatosensory cortex “shrinks” or shifts, which correlates with the patient’s perceived neglect of the limb.

3. The Clinical Diagnosis: The Budapest Criteria

Because there is no “gold standard” lab test or imaging for CRPS, the diagnosis is purely clinical. The Budapest Criteria are used to provide high sensitivity and specificity.

To make a diagnosis, the patient must have:

1. Continuing pain, which is disproportionate to any inciting event.
2. Must report at least one symptom in three of the four following categories:
   • Sensory: Reports of hyperesthesia and/or allodynia.
   • Vasomotor: Reports of temperature asymmetry and/or skin color changes/asymmetry.
   • Sudomotor/Edema: Reports of edema and/or sweating changes/asymmetry.
   • Motor/Trophic: Reports of decreased range of motion and/or motor dysfunction (weakness, tremor, dystonia) and/or trophic changes (hair, nail, skin changes).
3. Must display at least one sign at the time of evaluation in two or more of the same categories.

4. Interventional Management

Interventions in CRPS are aimed at “breaking the cycle” of pain to allow for participation in physical therapy.

• Sympathetic Nerve Blocks:
  • Stellate Ganglion Block (SGB): For upper extremity symptoms. The target is the anterior tubercle of the C6 transverse process (Chassaignac’s tubercle) or the C7 level.
  • Lumbar Sympathetic Block: For lower extremity symptoms. The target is the anterolateral aspect of the L2, L3, or L4 vertebral bodies.
• Spinal Cord Stimulation (SCS): Indicated for refractory CRPS. SCS is particularly effective for the neuropathic and vasomotor components of the disease.
• Dorsal Root Ganglion (DRG) Stimulation: Newer evidence suggests that DRG stimulation may be superior to traditional SCS for focal CRPS (e.g., CRPS limited to the foot or knee) because it can target specific dermatomes more precisely.

5. Pharmacological Adjuncts

The medication strategy focuses on the various mechanisms involved:

• Neuropathic Agents: Gabapentinoids (Gabapentin/Pregabalin) and TCAs/SNRIs to address central sensitization.
• Bisphosphonates: (e.g., Alendronate, Pamidronate) have shown efficacy in the early, inflammatory stages of CRPS, particularly when there is evidence of bone marrow edema on MRI.
• Ketamine Infusions: Low-dose NMDA receptor antagonism can help “reset” the centralized pain state.
• Topical Agents: Capsaicin or Lidocaine patches for localized allodynia.

6. The “GMI” Protocol

Physical and occupational therapy are the primary treatments, not just adjuncts. The goal is functional restoration.

• Graded Motor Imagery (GMI): A three-stage process to address cortical reorganization:
  1. Laterality Training: Identifying left vs. right limbs to restore the brain’s internal map.
  2. Explicit Imagery: Mentally practicing movements without actually moving.
  3. Mirror Therapy: Using a mirror to “trick” the brain into seeing the painful limb move normally by observing the reflection of the healthy limb.
• Desensitization: Gradually exposing the limb to different textures (silk, wool, etc.) to reduce allodynia.
• Stress Loading: Specific to the hand (Scrub-and-Carry protocol), this involves weight-bearing and compression to normalize sensory input.

---

High-Yield Board “Fast Facts”

• Vitamin C: Daily administration of 500mg for 50 days following a distal radius fracture has been shown in some studies to reduce the incidence of developing CRPS.
• Triple-Phase Bone Scan: Classically shows increased periarticular uptake in the third (delayed) phase, but its absence does not rule out CRPS.
• Bone Demineralization: Long-standing CRPS can lead to Sudeck’s Atrophy (patchy osteoporosis) visible on X-ray.
• Spread: CRPS can occasionally “spread” to another limb, which can be contiguous, mirror-image, or independent.