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Complex Regional Pain Syndrome

March 10, 2016  |  Posted by: Sam Menteith

Complex Regional Pain Syndrome (CRPS) is a chronic progressive medical condition characterised by severe pain, often accompanied by sensory and motor neurological abnormalities, swelling and changes in the skin and frequently complicated by mood disorder, significant loss of function and subsequent disability.

What is it?
The term complex regional pain syndrome (CRPS) was devised to replace out-dated terminology (such as Reflex Sympathetic Dystrophy) for a condition characterised by spontaneous or stimulus-induced pain that is disproportional to the provoking event and accompanied by many neurological disturbances (autonomic, sensory and motor) in variable combinations. The term ‘Reflex Sympathetic Dystrophy’ was based on the theory that sympathetic overactivity was involved in the condition’s functional development. However, misuse of the term and doubts about its underlying cause, led to the present diagnostic term naming. CRPS has been subdivided into type I and type II. CRPS I encompass disorders without a nerve injury; while CRPS II occurs after damage to a peripheral nerve.

Cause of CRPS
The cause of CRPS is unknown. Precipitating factors include injury (sometimes apparently trivial injury) and most commonly fractures, sprains, and surgery, but also include injections, local infections, burns, frostbites, pregnancy, stroke or myocardial infarction. The exact nature and combination of symptoms of CRPS and their severity are not related to the severity of trauma. The median nerve and the sciatic trunk are involved in ~60% of upper and lower extremity CRPS type II. More than 10% of patients may not recall any precipitating event or demonstrable injury to the original site. In CRPS surgery and other medical procedures used in the treatment of the original injury may contribute to the progression of the syndrome.

Numerous pathophysiological events have been incriminated in development of CRPS, including inflammation, autoimmune responses, abnormal cytokine production, sympathetic-sensory disorders, altered blood flow and central cortical reorganisation or plasticity.

It is likely that some patients with CRPS have abnormal pain systems which respond in a dysfunctional way to pain stimuli. In susceptible people uninhibited do so called ‘wind-up’ of pain circuits in the spinal cord and the brain described as ‘central sensitisation’ results in chronic pain and distress and commonly leads to dysfunctional mood and behaviour.

CRPS can affect a person of any age. The mean age at diagnosis is 42. It is three times more frequent in females than males. It has been estimated that CRPS may occur in approximately 2-5% of those with peripheral nerve injury. It is common in patients with hemiplegia (paralysis of one side of the body). Population-based studies have established the incidence of CRPS (about 20/100 000), and distinct risk factors for CRPS. Although most patients recover within 12 months, CRPS may result in severe chronic pain for some.

The symptoms (pain, sensory, autonomic, trophic and motor symptoms) of CRPS initially manifest near the site of an injury and usually spread distally beyond the original area. Symptoms may spread to involve the entire limb and, commonly, the opposite limb, and to the neck and head, and occasionally the whole body. Frequently CRPS is complicated by sleep, mood and behavioural disturbance.

The major characteristic of CRPS is pain that is out of proportion in both intensity and duration to the original injury or trauma and not limited to a single nerve territory. It can be spontaneous and continuous, episodic or undulating or arise in response to physical and often also emotional stimuli. Patients with CRPS type II almost invariably describe their pain as burning.

The majority of adult patients with CRPS exhibit combinations of sensory loss and gain. The most frequent pattern consists of increased sensitivity to painful stimuli and decreased perception of non-painful stimuli.

The most common symptoms are burning and electrical like shooting pains. Other manifestations may include: abnormal sensory perception (normal stimuli may cause pain), muscle spasms, local swelling, increased sweating, changes in skin temperature and colour, softening and thinning of bones, joint tenderness or stiffness, restricted or painful movement, and changes in the nails, dry skin, and rapid shedding of skin.

Patients with CRPS may also display referred sensations, i.e., the referral of somatosensory feelings to areas that are adjacent in the cortical brain map, or mislocalisation of tactile stimuli and a variety of other sensory abnormalities including the perception of pain or odd sensations when watching a mirror image of the unaffected limb being stimulated by light touch or pressure in a region that corresponds to an area of allodynia or paresthesia on the painful extremity (dysynchiria). Perception of a stimulus in both the affected and unaffected extremities when the stimulus is applied to the healthy limb in a region corresponding to an area of paresthesia (synchyria). A unilateral tactile stimulus is perceived only in the analogous location on the opposite extremity (allochiria). Simultaneous bilateral tactile stimulation is perceived in only one limb (sensory extinction).

A vast majority of patients with CRPS have some sort of motor disturbance, most commonly weakness or limited active range of motion. Tendon reflexes are frequently exaggerated. Severe movement disorders such as muscle spasms, myoclonus, and dystonia and/or postural tremors have been reported.

Symptoms of CRPS vary in severity and duration. Moving or touching the limb is often intolerable and pain may be magnified by emotional stress. Eventually the joints may well become stiff from disuse, and the skin, muscles and bone become wasted and thinned.

There is no diagnostic test for CRPS. The diagnosis of CRPS is based on the history and clinical examination. Investigations (radiology, nerve conduction studies, bone scans) are used to exclude other diagnoses.

Consensus-based diagnostic criteria for CRPS have been much debated due to the obscure nature of CRPS, absence of definitive objective tests to confirm its existence and lack of a strong evidence base. The result is over or under diagnosis of the condition depending on the choice of diagnostic criteria. Currently the Budapest clinical criteria are the most widely accepted for diagnosis of CRPS. Although these criteria have been adopted by the AMA Guides 6th edition the highly controversial use of the impractical and widely criticised CRPS diagnostic criteria in the 5th edition made it almost impossible to diagnose the condition for medicolegal doctors working in those jurisdictions that rely on the AMA 5th edition for the purposes of rating permanent impairment.

Early recognition and prompt treatment of pain and complicating factors, including mood disturbance, provide the greatest opportunity for recovery. The general strategy in CRPS treatment is often intensive and multidisciplinary, using different types of medications combined with physical therapies.

Physicians use a variety of drugs to treat CRPS, including antidepressants, nonsteroidal anti-inflammatories and anticonvulsants, as well as opioids, local nerve blocks and ketamine. These drugs have a high capacity for side effects and frequently cause drowsiness, poor concentration and impair mood and motivation.

Physical and occupational therapy works best for most patients, especially goal directed therapy, where the patient begins from an initial point, regardless of how minimal, and then endeavours to increase activity each week. People with CRPS often avoid using or touching the affected limb, with this inactivity exacerbating the disease and perpetuating the pain cycle. Thus, therapy is usually directed at facilitating the patient’s engagement in physical therapy, movement and stimulation of the affected areas.

Neurostimulation (spinal cord stimulator) might be surgically implanted to reduce the pain by directly stimulating the spinal cord. Implantable drug pumps may also be used to deliver pain medication directly to the cerebrospinal fluid – allowing powerful opioids to be used in much smaller doses than when taken orally. Surgical, chemical, or radiofrequency sympathectomy – interruption of the affected portion of the sympathetic nervous system – have been used as a last resort in patients. However, there is little evidence that these permanent interventions alter the outcomes for the better. EEG Biofeedback, psychotherapy, relaxation techniques and hypnosis are adjunctive treatments that may assist coping.

The prognosis is more commonly better if treatment of pain and mood disturbance is begun early, ideally within three months of the first symptoms. Delayed treatment may cause irreversible changes in bone, nerve, muscle, mood and behaviour, leading to severe disability.