31st January 2024

CRPS

Unilateral limb pain commonly presents to general practitioners, and there is a wide range of differentials. Again, the history is very important, particularly noting prior trauma or surgery. With a history of preceding notable trauma, bone or soft tissue injury, joint instability, and ligamental damage should be ruled out with imaging. 

Nerve injury 

Nerve injury can occur at the level of the spinal cord, spinal root, or peripheral nerve. Spinal cord injuries, specifically cauda equina lesions, present with bilateral symptoms. Nerve entrapment at the lumbar spinal root classically causes radicular pain from the back to the legs, sensory disturbances, and weakness. Peripheral nerve entrapment or injury also causes pain, sensory disturbance, and weakness. Clinical examination is key as CRPS does not affect specific dermatomes, myotomes and the specific distribution of peripheral nerves as seen in these conditions. 

Peripheral Vascular Disease (PVD)

PVD can present with similar symptoms to CRPS; however, it is classically bilateral, associated with night pain and intermittent claudication. Patients have cardiovascular risk factors such as older age, smoking, hypertension, diabetes and hypercholesterolaemia. Specifically for PVD, there are weak or absent pulses, arterial ulcers, and a positive Buerger test. A bedside ankle brachial pressure index can diagnose PVD. 

Infection 

Skin, soft tissue, bone or joint infections all present with unilateral limb pain. The lack of chronicity, fever and raised inflammatory markers differentiates this from CRPS.

Post-surgical complications

CRPS is a diagnosis of exclusion, and ongoing pathology should be excluded in post-operative patients. 

Compartment syndrome 

Compartment syndrome presents with unilateral severe pain, typically in the legs and often after trauma. Signs include swollen compartments and pain with any movement of the affected muscle. As opposed to CRPS, it is acute onset. 

Erythromelalgia

This condition is a rare neurovascular, peripheral pain disorder characterised by erythema, increased skin temperature and burning of the feet and hands, occurring periodically. Similar to CRPS, there can be reduced sweating in the affected area and swelling. Conversely to CRPS, there are triggers for erythromelalgia, including stress, heat such as hot baths, exercise, and insomnia. Erythromelalgia also tends to be bilateral and intermittent in nature, with pain-free periods.