Complex regional pain syndrome: what is it?

Have you ever had a fracture? If you have, then you are probably aware of how difficult it can be to recover. Today, we have Hannah Pickering, a neuroscientist in Sydney, who provides us with an update on complex regional pain syndrome, a poorly understood neurological disorder that may occur with limb immobilisation. Over to you, Hannah.

Complex Regional Pain Syndrome (CRPS) was formally known as causalgia, from the Greek word, kausis, -which means fire. It was later termed reflex sympathetic Dystrophy. While there is debate over the first description of the condition, Mitchell et al. (1) described the presentation of severe burning pain after tissue injury, in soldiers who had fought in the civil war. In his description, he highlighted the exaggerated nature of the pain in relation to the injury, which to date remains a primary feature of the current CRPS classification.

CRPS is a chronic neuropathic pain disorder, which occurs primarily after limb trauma and can be classified as CRPS I – when there is no nerve lesion evident, or CRPS II when a definable nerve lesion is present. A history of injury, most commonly fracture or soft tissue injury, followed by subsequent immobilisation are the most consistently associated factors with a diagnosis of CRPS (2, 3). Recent observational studies suggest that 47% of patients identify physician-imposed immobilisation (4), however, the frequency is likely to be higher, as immobilisation due to disuse and protective guarding has not yet been investigated.

CRPS is characterised by autonomic motor and sensory abnormalities. Patients can suffer an array of symptoms including burning pain, inflammation, sensory abnormalities (5), autonomic (2), trophic, and motor disturbances (2, 3). Hyperalgesia (increased pain from a stimulus that normally provokes pain) and allodynia (pain due to a stimulus that does not normally provoke pain) are frequently reported in patients suffering CRPS (2, 3, 6). Some patients also demonstrate clinical signs of oedema (2, 5).

The aetiology of CRPS to date remains unclear with a variety of possible mechanisms being evaluated. However a recent review identified three major pathophysiological pathways, namely,  abnormal inflammatory mechanisms, vasomotor dysfunction and maladaptive neuroplasticity (7) which independently or in combination, can result in CRPS. Research from Drummond and Finch, published in JNNP, raised the additional possibility of a central nervous system contribution to the amplification of pain in CRPS, which may lead to further disability and explain the condition’s resistance to treatment (8).

Interestingly, disturbances in the way one perceived their own body are frequently reported in chronic pain conditions. Mosley and colleges demonstrated that sixty-three percent of patients with CRPS identified with an expanded image of their affected limb compared to only 7% of controls (9)  Additionally, studies using magnetoencephalography (MEG) revealed that the somatosensory representation (or a map of the body surface) of the limb affected by CRPS was significantly smaller than the healthy limb(10). Furthermore, reduction in CRPS pain through physiotherapy and pharmacological intervention, was correlated with recovery from cortical representation (11). This relationship raised the possibility that S1 changes mediated the increased perceived limb size experienced by CRPS patients (10), although the mechanisms that brought about this change remain unclear.

Recent evidence suggests that chronic pain distorts the processes of motor imagery.Recognition of whether a viewed image is of a left or right side is classified as a motor imagery task. Correctly identifying laterality, involves mentally moving one’s own body part to adopt the position of a pictured body part. It depends on an working intact body schema, brain-grounded maps of the body that are used for planning executing movements and are constructed, in-part, from real-time proprioceptive input (9). Studies have shown that CRPS patients take longer to recognise images corresponding with their affected limb (12).

In terms of treatment, the primary aims are first controlling the pain, followed by rehabilitation of the affected limb. An array of treatments options are utilised , often in combination and include; physical therapy (Graded motor imagery and mirror box therapy), pharmacologic therapies, anaesthesia techniques such as nerve blocks, and more recently neuromodulation. One focus of current research targets potential effects of high frequency spinal cord stimulation as a novel treatment approach in this condition.

 

References:

1)      Mitchell SW, Morehouse GR, Keen WW. Gunshot Wounds and Other Injuries of Nerves. Vol: 100. Philadelphia: J. Lippincott and Co.; 1864: 11.

2)      Birklein F, Riedl B, Sieweke N, Weber M, Neundorfer B (2000). Neurological findings in complex regional pain syndromes–analysis of 145 cases. ActaNeurolScand101,262-269.

3)      Birklein F (2005). Complex regional pain syndrome. J Neurol 252,131-138.

4)      Allen G, Galer BS, Schwartz L (1999). Epidemiology of complex regional pain syndrome: a retrospective chart review of 134 patients. Pain.  80,539-544.

5)      Huge V, Lauchart M, Forderreuther S, Kaufhold W, Valet M, Azad SC, et al. (2008). Interaction of hyperalgesia and sensory loss in complex regional pain syndrome type I (CRPS I). PLoS One. 3,2742.

6)      Terkelsen AJ, Bach FW, Jensen TS (2008). Experimental forearm immobilization in humans induces cold and mechanical hyperalgesia. Anesthesiology. 109,297-307.

7)      Marinus J, Moseley GL, Birklein F, Baron R, Maihöfner C, Kingery WS, van Hilten JJ. (2011) Clinical features and pathophysiology of complex regional pain syndrome.Lancet Neurology. 10(7):637-48.

8)      Drummond P and Finch PM. Persistence of pain induced by startle and forehead cooling after sympathetic blockade in patients with complex regional pain syndrome. J Neurol Neurosurg Psychiatry 2004;75:98-102

9)      Moseley GL (2005). Distorted body image in complex regional pain syndrome. Neurology. 65,773.

10)   Maihofner C, Handwerker HO, Neundorfer B, Birklein F (2003). Patterns of cortical reorganization in complex regional pain syndrome. Neurology. 61,1707-1715.

11)   Maihofner C, Handwerker HO, Neundorfer B, Birklein F (2004a). Cortical reorganization during recovery from complex regional pain syndrome. Neurology. 63,693-701.

12)   Moseley GL (2004). Why do people with complex regional pain syndrome take longer to recognize their affected hand? Neurology. 62,2182-2186.