Reversal of hypoaesthesia by nerve block, or placebo: a psychologically mediated sign in chronic pseudoneuropathic pain patients

Complex regional pain syndrome and functional neurological disorders - time for reconciliation

There have been many articles highlighting differences and similarities between complex regional pain syndrome (CRPS) and functional neurological disorders (FND) but until now the discussions have often been adversarial with an erroneous focus on malingering and a view of FND as 'all in the mind'. However, understanding of the nature, frequency and treatment of FND has changed dramatically in the last 10-15 years. FND is no longer assumed to be only the result of 'conversion' of psychological conflict but is understood as a complex interplay between physiological stimulus, expectation, learning and attention mediated through a Bayesian framework, with biopsychosocial predisposing, triggering and perpetuating inputs. Building on this new 'whole brain' perspective of FND, we reframe the debate about the 'psychological versus physical' basis of CRPS. We recognise how CRPS research may inform mechanistic understanding of FND and conversely, how advances in FND, especially treatment, have implications for improving understanding and management of CRPS.

Functional sensory symptoms

Functional (psychogenic) sensory symptoms are those in which the patient genuinely experiences alteration or absence of normal sensation in the absence of neurologic disease. The hallmark of functional sensory symptoms is the presence of internal inconsistency revealing a pattern of symptoms governed by abnormally focused attention. In this chapter we review the history of this area, different clinical presentations, diagnosis (including sensitivity of diagnostic tests), treatment, experimental studies, and prognosis. Altered sensation has been a feature of "hysteria" since descriptions of witchcraft in the middle ages. In the 19th century hysteric sensory stigmata were considered a hallmark of the condition. Despite this long history, relatively little attention has been paid to the topic of functional sensory disturbance, compared to functional limb weakness or functional movement disorders, with which it commonly coexists. There are recognizable clinical patterns, such as hemisensory disturbance and sensory disturbance finishing at the groin or shoulder, but in keeping with the literature on reliability of sensory signs in neurology in general, the evidence suggests that physical signs designed to make a positive diagnosis of functional sensory disorder may not be that reliable. There are sensory symptoms which are unusual but not functional (such as synesthesia and allochiria) but also functional sensory symptoms (such as complete loss of all pain) which are most unusual and probably worthy of independent study.

Nondermatomal somatosensory deficits: overview of unexplainable negative sensory phenomena in chronic pain patients

PURPOSE OF REVIEW

To review the literature and our current understanding of nondermatomal somatosensory deficits (NDSDs) associated with chronic pain in regards to their prevalence, assessment and clinical presentation, cause and pathophysiology, relationship with conversion disorder and psychological factors, as well as their treatment and prognosis.

RECENT FINDINGS

NDSDs are negative sensory deficits consisting of partial or total loss of sensation to pinprick, light touch or other cutaneous modalities. Although they had been noted more than a century ago and appear prevalent in chronic pain populations, they are poorly studied. They may be very mild or very dense, may occupy large body areas, are often highly dynamic and changeable or, to the contrary, very stable and long lasting. NDSDs may occur in the absence of biomedical pathology or coexist with structural musculoskeletal or nervous system abnormalities. They appear to be associated with psychological factors and a poor prognosis for response to treatment and return to work. Recent brain imaging studies provide a basis for understanding NDSD pathophysiology.

SUMMARY

NDSDs represent prevalent phenomena associated with chronic pain. Further, research is needed to elucidate their origin, response to treatment, and prevalence in the general population, primary care settings, and nonpain patients.

Neuropathic pain syndrome displayed by malingerers

Among 237 patients communicating chronic pain, associated with sensory-motor and "autonomic" displays, qualifying taxonomically for neuropathic pain, there were 16 shown through surveillance to be malingerers. When analyzed through neurological methods, their profile was characteristically atypical. There were no objective equivalents of peripheral or central processes impairing nerve impulse transmission. In absence of medical explanation, all 16 had been adjudicated, by default, the label complex regional pain syndrome (CRPS). The authors emphasize that CRPS patients may not only harbor unrecognized pathology ("lesion") of the nervous system (CRPS II), hypothetical central neuronal "dysfunction" (CRPS I), or conversion disorder, but may display a recognizable simulated illness without neuropsychiatric pathology.

FMRI in patients with motor conversion symptoms and controls with simulated weakness

BACKGROUND

Conversion disorder (motor type) describes weakness that is not due to recognized disease or conscious simulation but instead is thought to be a "psychogenic" phenomenon. It is a common clinical problem in neurology but its neural correlates remain poorly understood.

OBJECTIVE

To compare the neural correlates of unilateral functional weakness in conversion disorder with those in healthy controls asked to simulate unilateral weakness.

METHODS

Functional magnetic resonance imaging (fMRI) was used to examine whole brain activations during ankle plantarflexion in four patients with unilateral ankle weakness due to conversion disorder and four healthy controls simulating unilateral weakness. Group data were analyzed separately for patients and controls.

RESULTS

Both patients and controls activated the motor cortex (paracentral lobule) contralateral to the "weak" limb less strongly and more diffusely than the motor cortex contralateral to the normally moving leg. Patients with conversion disorder activated a network of areas including the putamen and lingual gyri bilaterally, left inferior frontal gyrus, left insula, and deactivated right middle frontal and orbitofrontal cortices. Controls simulating weakness, but not cases, activated the contralateral supplementary motor area.

CONCLUSIONS

Unilateral weakness in established conversion disorder is associated with a distinctive pattern of activation, which overlaps with but is different from the activation pattern associated with simulated weakness. The overall pattern suggests more complex mental activity in patients with conversion disorder than in controls.

Spectrum of cutaneous hyperalgesias/allodynias in neuropathic pain patients

OBJECTIVES

The aim of this study was to discern the pathophysio-logical bases for neuropathic hyperalgesias.

METHODS

In this study, neurological and neurophysiological evaluation of 132 consecutive hyperalgesia patients using rigorous clinical and laboratory protocols were carried out.

RESULTS

Two discrete semeiologic entities emerged: classic neurological vs atypical, fulfilling taxonomically complex regional pain syndrome (CRPS) II and I, respectively. The classic group (34.9%) exhibited sensorimotor patterns restricted to nerve distribution and documented nerve fiber dysfunction. Among them four (3.03%) had sensitization of C-nociceptors, seven (5.3%) had central release of nociceptive input, and 35 (26.52%) probable ectopic nerve impulse generation. The atypical group (65.1%) displayed weakness with interrupted effort; non-anatomical hypoesthesia and hyperalgesia; hypoesthesia or paresis reversed by placebo, or atypical abnormal movements, and physiological normality of motor and sensory pathways.

CONCLUSIONS

Spatiotemporal features of neuropathic hyperalgesia constitute key criteria for differential diagnosis between CRPS II and I and, together with other behavioral sensorimotor features, signal psychogenic pseudoneurological dysfunction vs structural neuropathology. 'Neuropathic' hyperalgesias may reflect neuropathological or psychopathological disorders.

Randomised controlled trial of gabapentin in Complex Regional Pain Syndrome type 1 [ISRCTN84121379]

Background

Complex Regional Pain Syndrome type one (CRPS I) or formerly Reflex Sympathetic Dystrophy (RSD) is a disabling syndrome, in which a painful limb is accompanied by varying symptoms. Neuropathic pain is a prominent feature of CRPS I, and is often refractory to treatment. Since gabapentin is an anticonvulsant with a proven analgesic effect in various neuropathic pain syndromes, we sought to study the efficacy of the anticonvulsant gabapentin as treatment for pain in patients with CRPS I.

Methods

We did a randomized double blind placebo controlled crossover study with two three-weeks treatment periods with gabapentin and placebo separated by a two-weeks washout period. Patients started at random with gabapentin or placebo, which was administered in identical capsules three times daily. We included 58 patients with CRPS type 1.

Results

Patients reported significant pain relief in favor of gabapentin in the first period. Therapy effect in the second period was less; finally resulting in no significant effect combining results of both periods. The CRPS patients had sensory deficits at baseline. We found that this sensory deficit was significantly reversed in gabapentin users in comparison to placebo users.

Conclusions

Gabapentin had a mild effect on pain in CRPS I. It significantly reduced the sensory deficit in the affected limb. A subpopulation of CRPS patients may benefit from gabapentin.

Treatment of complex regional pain syndrome type I

Reflex sympathetic dystrophy (RSD), also known as complex regional pain syndrome type I (CRPS I), is a disabling neuropathic pain syndrome. Controversy exists about the effectiveness of therapeutic interventions for the management of RSD/CRPS I. In order to ascertain appropriate therapies we conducted a review of existing randomized controlled trials of therapies for this disabling disease. Eligible trials were identified from the Cochrane, Pubmed, Embase and MEDLINE databases from 1966 through June 2000, from references in retrieved reports and from references in review articles. Twenty-six studies concerning treatment modalities were identified. Eighteen studies were randomized placebo-controlled trials and eight studies were randomized active-controlled trials. Three independent investigators reviewed articles for inclusion criteria using a 15-item checklist. Seventeen of the trials were of high quality according to the 15-item criteria. There was limited evidence for the effectiveness of these interventions because of the heterogeneity of treatment modalities. The search for trials concerning prevention of RSD/CRPS I resulted in two eligible studies. Both were of high quality and dealt with different interventions. There is limited evidence for their preventive effect.

Controversies surrounding reflex sympathetic dystrophy: a review article

The topic of reflex sympathetic dystrophy (RSD) has generated an increasingly significant volume of medical literature and controversy over the last decade. A search of PubMed, the online site of the National Library of Medicine, for papers on RSD reveals nearly 2200 articles on the topic (using algodystrophy as the search word, wherein RSD references are also included, and more older and European articles are also listed). From 1991 through 1998 inclusive there is an average of nearly 100 articles per year on the topic, which represents more than a third of all the articles referenced since 1965. In the decade of the 1980s, there is an average of 64 articles per year, 74 per year in the last half of the decade and 54 per year in the first half. Prior to the decade of the 1980s, one finds an average of 40 articles per year back to the mid-1960s. The controversy surrounding the disorder centers around the nature of the problem and whether it is a primary organic disorder or a primary psychogenic disorder associated with the accomplishment of some secondary gain. If it is the former, then clearly research should continue to determine the nature and etiology of the malfunctioning organ(s). If, on the other hand, RSD is a psychogenic disorder, then the medical community does well to focus mainly on the peripheral manifestations of the problem. In that instance, therapy should be primarily psychological and cognitive with regard to the secondary gain, and persistent organic treatments are unlikely to improve the condition in general and worsen individual cases.

Abnormal movements in complex regional pain syndrome: assessment of their nature

Abnormal movements may be a clinical feature in complex regional pain syndrome (CRPS), but their basic nature is unclear. Between August 1989 and September 1998, patients fulfilling diagnostic criteria for CRPS (I or II) and displaying abnormal movements were entered into a prospective study. Fifty-eight patients, 39 women and 19 men, met entry criteria; 47 had sustained a minor physical injury at work. The patients exhibited various combinations of dystonic spasms, coarse postural or action tremor, irregular jerks, and, in one case, choreiform movements. Patients underwent rigorous clinical and laboratory evaluation aimed at characterizing their neurological disturbance. Surprisingly, no case of CRPS II but only cases of CRPS type I displayed abnormal movements. In addition to an absence of evidence of structural nerve, spinal cord, or intracranial damage, all CRPS I patients with abnormal movements typically exhibited pseudoneurological (nonorganic) signs. In some cases, malingering was documented by secret surveillance. This study highlights abnormal movements in CRPS as constituting a key clinical feature that differentiates CRPS I from CRPS II. They are consistently of somatoform or malingered origin, signaling an underlying psychoneurological disorder responsible for the entire CRPS profile.