Complex regional pain syndrome (CRPS)
Complex regional pain syndrome (CRPS) is a chronic pain condition characterised by a ‘neuropathic’ type pain that is disproportionate in duration or degree to the usual course of any known trauma or condition such as nerve damage. As a diagnosis of exclusion, no other disease or condition should be present which might explain the symptoms or signs used to diagnose CRPS. It is seen in the pain medicolegal context in patients presenting with chronic pain in a limb, some time after the index event in question.
CRPS is a condition that provides a useful case study of the challenges surrounding classification, diagnosis, causality, treatment and effects on patients, that often arise in wider medicolegal settings.
Classification, epidemiology and aetiology
The aetiology or exact causes are unknown today. CRPS is classified into Types 1 and 2, the latter arising out of a specific nerve injury. However, this divide has no particular usefulness, given that the manifestation and treatment options are generally the same. Older terms for the condition include causalgia, reflex sympathetic dystrophy and Sudeck’s atrophy, but these are no longer used. CRPS is a rare condition, and the European incidence rate is estimated at 26/100,000 person years. It is approximately twice as frequent in females than in males, and tends to affect upper limbs more often. It also occurs in the paediatric population. While the cause is uncertain, inflammation, the immune system and sensitisation of nerves are important in its development. Studies associate increased frequency of CRPS with certain genes, implying a genetic / hereditary factor in CRPS.
The most common precipitating events leading to CRPS are trauma and surgery, but in some cases no specific injury can be identified. It has also been noted to arise from trivial injuries such as needlestick injuries and sprains. Orthopaedics thus probably see the highest numbers of CRPS in the initial stages, given that it can occur with any trauma or surgery. It often arises insidiously, with an evolving presentation over time; and thus a high index of suspicion is required for its diagnosis.
Symptoms, signs and diagnosis
The records after an index accident may give clues as to when CRPS started, or whether it was present at all. The symptoms (what the patient states in their history of complaints) of CRPS are variable, and lie on a spectrum of severity in different patients.
The pain is normally described in ‘neuropathic’ terms, including burning, stabbing, electrical and pins and needles. The patient may also experience swelling, changes in sweating, and skin temperature, either hot or cold. The skin can undergo colour changes such as bluish mottling or redness. Other changes include skin texture, nails and hair growth, spasms, tremors and dystonia.
The diagnosis of CRPS is clinical, and no laboratory or radiological test can definitively exclude or diagnose the condition. This relies on the symptoms described above, and on establishing corresponding signs (what the medical professional finds on examination). The original diagnostic criteria for CRPS adopted by the International Association for the Study of Pain (IASP) in 1994 have now been superseded in both clinical practice and research by the ‘Budapest Criteria’, which were created in 2003. These new criteria are more specific (that is to say, they yield less overdiagnosis). The stricter ‘rules’ reflect in themselves the diagnostic problems of CRPS encountered in the past. The implication here is that CRPS is too often diagnosed when not present.
On questioning a patient, it is common that many symptoms are present at some point during their course of pain; and so the criteria for symptoms are commonly fulfilled. However, a minimum number of signs on physical examination must be present – and this can rule CRPS in or out.
Bass and Yates (Ref 2), opining on CRPS in the medicolegal context, comment on the lack of inter-rater reliability in the diagnosis of CRPS. In their sample, they found many cases involving either disagreement between the treating clinician and the medicolegal expert, or a disagreement between medicolegal experts, which led to obvious problems in litigation.
As stated earlier, there is no test that can confirm or refute the diagnosis, and clinical examination might be subject to interobserver variation – especially when the clinical signs are mild. For example, a slight discolouration of a hand used as a sign for diagnosis might not be obvious, or deemed sufficient as a positive diagnostic criterion between clinicians.
There are, of course, other reasons for a range of opinion, given the clinical nature and diversity of signs in CRPS. Lazaro (Ref 4) states that most patients encountered delay in diagnosis and treatment owing to the lack of ‘typical’ objective signs of CRPS, and the patients’ symptoms were said to fluctuate at different times of the day.
In the past, patients were hypothesised to have a psychological predisposition to develop CRPS; but the literature has rejected this suggestion (Ref 1). Goebel further states in the article that when patients do present with significant psychiatric or psychological comorbidity, it should be assumed that this was either a coincidence, or in response to having CRPS. This implies that there is no personality, psychological trait or psychiatric condition that renders one more vulnerable to develop the disease. According to Bass and Yates, as previously referred to (Ref 2), patients diagnosed with CRPS who become involved in litigation were said to have high rates of previous psychopathology, especially somatoform disorders and pain related disabilities involving opioid use.
The issues here are clearly complex: from a pain perspective, patients with previous psychological problems such as mood disorders are predisposed to further such disorders. This might occur especially in the face of stressors including any chronic pain condition such as CRPS. A psychological expert is normally helpful in opining on these issues.
Physical therapy and increased mobility / movements in the affected limb as early as possible are regarded as vital treatments if CRPS is diagnosed. This would
involve early referral to hand physiotherapy for example, and compliance with exercise is emphasised. Education regarding the disease and early referral to pain management is important.
Many treatment modalities are used for CRPS, and their efficacies can be considered medium / low in general, although some patients do respond to certain treatments with good results. Anti-neuropathic medications are employed, such as pregabalin, amitriptyline and duloxetine. Topical agents such as lidocaine patches and Capsaicin 8% have also been used. Other options include bisphosphonates, calcitonin, ketamine, and Botox; but these also have low / moderate evidence of efficacy in CRPS. In terms of pain interventions, day case injections called ‘sympathectomies’ can be performed both for upper or lower limbs. These can be followed on by radiofrequency treatments if the former are successful (electrical induced lesioning / modulating of the nerves perpetuating pain). The responses are not guaranteed, but if successful, can assist in rehabilitation. Patient selection is important for success, and is guided by variables such as pain severity and psychological factors.
Spinal cord stimulators (SCS) are electrodes implanted around the spinal cord or nerves, stimulating these structures to produce pain control. They feature in the NICE guidelines as a recommended treatment for CRPS.
SCS systems are considered a major undertaking, and require multidisciplinary assessment and regular ongoing support. Patients have to be able to manage such systems and comply with the treatment for extended periods. In addition to these, serious complications can also occur, so careful patient selection and thorough assessment is vital for its implementation and success. It is costly and suitable for a minority of CRPS patients only.
Pain Management or Functional Restoration Programs (FRP) are biopsychosocial rehabilitation programs for chronic pain, and might benefit patients with CRPS. They employ concentrated psychological, physiotherapy and occupational therapy type treatments, for example, delivered over a few weeks. These are varied and can be as inpatient (for example two weeks’ full time in hospital) or outpatients (for example two days a week over six weeks). There are also bespoke and one to one type FRPs specific to the patient’s individual requirements, rather than group programs.
Given the range of treatments available – that is, from physiotherapy to spinal cord stimulation implants – the clinician should be guided by their assessment of the patient’s characteristics, pain severity and disabilities in making recommendations.
Cowell et al (Ref 3) observe that from an orthopaedic perspective (Ref 3), transient CRPS has been reported as a relatively common occurrence early after wrist fractures (up to a third of cases). CRPS can occur within a few months of any limb injury or surgery, but the article points to overdiagnosis if diagnostic criteria were not followed.
It further states that about 80% of patients with CRPS will improve significantly within the first year after trauma, and about a third of patients consider themselves fully recovered at six years. However, up to 20% of patients will have persistent symptoms, and never fully recover. There are also descriptions of CRPS spreading to other limbs, and the course being one of remission and relapse over time. In the medicolegal context, the evolving situation of the disease can influence outcomes: the patient can improve or deteriorate over a period of time before settlement.
CRPS remains a condition which is little understood, and remains challenging to treat in the pain clinic.
The spectrum of presentation is very variable: some patients have a severe and debilitating course of the disease which causes marked disabilities and psychological distress, while some have mild symptoms and are able to live relatively normal lives.
The prognosis, treatments employed, requirements for assistance in self-care and daily activities would depend very much on the individual case, and careful study of the records available and examinations over time are important in providing an opinion in these domains.