Case of the Month #37: Complex Regional Pain Syndrome by Dr Sunil Dasari

What is Complex Regional Pain Syndrome (CRPS)?

Complex regional pain syndrome (CRPS) is a syndrome characterised by a non-dermatomal distribution, severe, continuous pain in the affected limb and is associated with sensory, motor, vasomotor, sudomotor and trophic disturbances¹.
When there is tissue damage like after trauma or surgery, we experience pain which will subside once the healing process is completed without many features of autonomic dysfunction. In CRPS we see that the pain is not only disproportionate to the injury, but also  associated with changes related to autonomic dysfunction.
CRPS is mostly precipitated after trauma or surgery. Upper limbs are more commonly affected  than lower limbs¹. The incidence is 5-26 per 100000². CRPS can occur in anyone at any age, with the mean age of diagnosis peaking at 40-50 years². It is reported 3-4 times more in females than in males². Less than 10 percent of patients with CRPS report no casual injury or trauma².
Two types are described: type 1, where there is no distinct demonstrable nerve lesion, and type 2, where a demonstrable nerve lesion is present.
The available evidence suggests that transient CRPS is common after limb fractures and orthopaedic operations (up to 25% of cases). The pain improves in most cases and CRPS lasting longer than a few months is an uncommon condition although even a transient episode of CRPS may give rise to long-term disability due to structural and/or functional changes³.
 

Pathophysiology

The pathophysiology is multifactorial with the most commonly accepted one being of exaggerated inflammatory response with autonomic nervous system dysfunction.
Different pathophysiology includes²:

• Hyperactivity of the sympathetic nervous system and vasomotor disturbance
• Neurogenic inflammation
• Deep-tissue microvascular pathology
• Autonomic dysregulation and small-fibre neuropathy
• Central processes: cortical reorganisation, central changes in pain processing
• Genetic predisposition: genetic factors, epigenetic factors
   

Clinical features

• Unprovoked or spontaneous pain that can be constant or fluctuate with activity.
• Excess or prolonged pain after use or contact. 
• Burning or pins and needle sensation, or as if the affected limb was being squeezed.
• Allodynia, in which light touch, normal physical contact, and use is very painful. Hyperalgesia where severe or prolonged pain after a mildly painful stimulus such as a pin prick.
• Changes in skin temperature, skin colour or swelling of the affected limb. The injured arm or leg may feel warmer or cooler than the opposite limb. Skin on the affected limb may change colour, becoming blotchy, blue, purple, grey, pale or red. These skin symptoms typically fluctuate as they indicate abnormal blood flow in the area.
• Changes in skin texture over time. Insufficient delivery of oxygen and nutrients can cause skin in the affected limb to change texture. In some cases, it becomes shiny and thin, in others thick and scaly.
• Changes in sweating and nail and hair growth. On the affected limb, hair and nails may grow abnormally rapidly, or not at all. Patches of profuse sweating or no sweating. All are under neural control and influenced by local blood circulation. 
• Stiffness in affected joints. Reduced movement leads to reduced flexibility of tendons and ligaments. Tight ligaments or tendons sometimes rub or pinch nerves to provide an internal cause of CRPS in people who do not have external injuries. 
• Wasting away muscles. In affected limbs, bones that receive signals from the damaged nerves rarely become affected. However, most patients report reduced ability to move the affected body part. This is usually due to pain and abnormalities in the sensory input that helps coordinate movements. 
• Rarely patients report abnormal movement in the affected limbs, fixed abnormal posture like dystonia, and tremors in or jerking. These can reflect secondary spread of disturbed neural activity to the brain and spinal cord. Most resolve by themselves during healing, but some people require orthopaedic surgery to lengthen contracted tendons and restore normal flexibility and position.