CHAPTER 81 Pain Dysfunction Syndrome

INTRODUCTION

Previous chapters of this book have dealt largely with the management of specific traumatic conditions and surgical reconstructive principles involved in the treatment of disorders of the elbow articulation. Necessarily, inferred but often understated in the discussion of these subjects is the inherent and inseparable consequence of some degree of pain experienced by normal individuals. Pain is defined as the perception of an unpleasant sensation that is generally localized to a specific anatomic region in response to a noxious stimulus (trigger) capable of producing potential or actual tissue damage.^19,^59,⁷³ Although unpleasant, the perception of acute pain serves an important physiologic function because it elicits a protective behavioral response outwardly noted as retraction from the noxious stimulus, followed by a transitory period of protection and guarding of the injured part.³⁷ Inseparable from the experience of acute pain is an individually variable emotional response that is dependent on the physiologic, psy-chological, cultural, and socioeconomic state of the person.^3,^29,¹⁴¹

Both postoperative pain and the temporary residual pain of recent injury are physiologic (functional) variants of acute pain.^63,¹⁴¹ Orthopedic surgeons generally have considerable clinical experience in dealing with a normal acute pain response and its variants by proceeding first with proper care of the injured part, administration of appropriate analgesics, and offering of emotional support and counseling. However, if during the course of initial treatment or the rehabilitation period a patient’s complaint of reported pain is judged to be extreme with respect to the known degree of tissue damage, or if the pain is abnormally prolonged, or the location and quality are poorly defined or nonspecific, then the possibility of a dysfunctional pain disorder must be considered when all plausible functional causes (e.g., compartment syndrome) have been eliminated.⁸⁹ The presentation of a patient’s dysfunctional pain response is most assuredly an unwelcome and worrisome complication, and often poses considerable challenges to the subsequent successful treatment and resolution of the presenting musculoskeletal problem. Moreover, following the recognition of dysfunctional pain, there is often a reasonable degree of consternation and possible indecision regarding the implementation of appropriate measures of management. Reasons for such indecision are well founded, because often the historical details, nature, and presentation of any patient’s dysfunctional pain pattern are individually variable, and clinical expertise is difficult to achieve in normal practice. Furthermore, until relatively recently, the amount of clinically relevant information on abnormal pain disorders within the musculoskeletal literature has been sparse, most often made up of anecdotal case studies.²⁹ The more detailed descriptive reports that are present in the literature have unfortunately been collectively categorized under a confusing array of terms (Box 81-1).

HISTORICAL PERSPECTIVE

The first of the terms in Box 81-1, causalgia (Gk., “burning”), was initially defined by S. Weir Mitchell, a Union surgeon during the Civil War.⁹⁶ Mitchell eloquently described a syndrome characterized by the onset of unrelenting intense, often burning, pain of an affected extremity, hypersensitivity, vasomotor disturbances, and the overzealous guarding of the injured part. Mitchell also described the consistent and profound psychological changes noted in affected patients, most of whom had sustained direct rifle ball wounds to major peripheral nerves of the upper extremity.^1,^2,^96,^124,¹⁴² After the war, Mitchell, Bernard, Leriche, and other noted physicians of the time, continued investigation of this and related pain disorders, primarily focused on the pathophysiologic basis for the observed autonomic nervous system disturbances, whereas other resear-chers proposed theories for a psychogenic basis of causalgia.^*

Most of the early investigative information from the study of causalgia and related disorders was derived from the evaluation of patients who had often sustained major injuries to the involved extremity. In 1953, Bonica proposed the term reflex sympathetic dystrophy (RSD) to define an abnormal pain syndrome clinically similar to causalgia that required sympathetic autonomic dysfunction as a major feature but was associated with an extremely varied range of etiologic factors.^1,^10,^115,¹³⁵ Associated events included both major and minor trauma, multiple types of surgical procedures, and repetitive occupational activities, and a collection of physiologically unrelated systemic diseases and idiopathic case examples.^1,^2,^10,^11,^109,^115,¹¹⁸

DEFINITION AND TERMINOLOGY

It is perhaps largely due to the confusing diversity of precipitating etiologic factors proposed by Bonica, as well as his prominent role in research in this area and the lack of any reproducible laboratory models to explain either a pathophysiologic relationship or the relative importance of these factors to the clinical development of RSD, that the term has been badly misused in the literature.^2,^4,^29,^120,¹⁴¹ Indeed, the term RSD has unfortunately evolved both in general clinical correspondence and in the medical literature to stand as a generic term for the presentation of any abnormal pain presentation or prolonged extremity dysfunction whether or not autonomic dysfunction exists.²⁹ The unfortunate end result of the continued clinical confusion and the generic use of the term RSD with respect to treatment implementation is that currently no consistent agreement exists regarding diagnostic criteria, natural history, and psychological factors involved in the syndromes listed in Box 81-1. These unresolved issues have often resulted in arbitrary clinical evaluation and anecdotal treatment protocols.^29,¹⁴¹ More recently, several authors have stressed the importance of distinguishing whether the sympathetic nervous system is involved by subcategorizing abnormal pain syndromes as sympathetically maintained pain or as sympathetically independent pain.^94,¹¹⁴

When a critical review of the literature is undertaken comparing the diagnostic criteria of each of the syndromes listed in Box 81-1 irrespective of the proposed etiologies or pathophysiologic factors, all clearly have two common denominators: an abnormal pain response and dysfunction of the affected extremity.^3,²⁹ From the recognition of this commonality of abnormal pain and extremity dysfunction among all the various pain syndromes and with the intent to rectify the perpetuation of the use of RSD as a generic label, Dobyns²⁹ and Amadio³ have recently recommended a more general term, pain dysfunction syndrome (PDS), to define such disorders. The use of the term PDS has several advantages. First, it is both clinically descriptive and sufficiently broad so as to encompass the diversity of possible precipitating factors and removes the contingency that sympathetic nervous system dysfunction exists in all cases of an abnormal pain presentation, which was necessarily implicit in the generic use of the term RSD.²⁹

By using PDS as a clinically descriptive label, the treating physician may then proceed without any nosologic hindrances to objectively differentiate, order, and subcategorize all the involved factors of a PDS into specific components.²⁹ These components include the physiologic characteristics of the injury and other sources of pain, any psychological manifestations, and the presence or absence of autonomic dysfunction.³ By proceeding in this logical fashion, the design of an effective and nonarbitrary treatment protocol can then be implemented (Fig. 81-1).

FIGURE 81-1 Treatment protocol for pain dysfunction syndrome.

PHYSIOLOGY AND PATHOPHYSIOLOGY OF PAIN

Before any further meaningful discussion on the clinical aspects of an abnormal pain response as a component of PDS can proceed, it is necessary to have an understanding of normal pain physiology. The sensation of normal acute pain begins with the interaction of a physical trigger (mechanical, thermal, and chemical) on a region of the body. Peripheral sensory nociceptors and mechanoreceptors are activated by the triggering event and transduce the physical energy into an electrochemical stimulus, which is then relayed proximally along the peripheral nerve via myelinated (Ad and Ab) and unmyelinated (C) fibers to synapse on wide dynamic range neurons of the dorsal horn of the spinal cord.^4,^53,^81,^93,^114,^136,^140,¹⁴¹ Further proximal propagation of the stimulus is then transmitted through the spinothalamic and spinoreticular pain pathways to central pain centers, which are located primarily within the midbrain, thalamus, and frontal cortex.^37,¹⁴⁰ Modulation of nociceptive stimulation occurs via central descending pathways and peripheral chemical factors.¹⁴ At the site of injury, should the physical trigger be of sufficient magnitude to produce tissue damage, local chemical modulators (hydrogen, potassium, bradykinin, serotonin, prostaglandins,¹⁶ substance P) are released from the damaged cells, which further activate and sensitize the peripheral receptors and focally produce the characteristic signs of edema, vasodilation, hyperpathia, and allodynia.^111,¹⁴¹ Provided that no ongoing or irreversible tissue damage occurs, both the cognitive perception of pain and the physiologic signs and symptoms of the acute pain dystrophic response subside.^37,^53,¹⁴⁰

The failure of any feature of the acute pain dystrophic response to resolve normally becomes a matter of clinical concern. In some cases, the abnormal persistence of pain may have a functional etiology, as when an unrecognized infection, synovial inflammation, ischemia, or nerve entrapment exists.³ Systemic factors such as rheumatologic disorders, endocrine or metabolic disorders (e.g., diabetic neuropathy), and the collagen vascular diseases can alter normal pain sensation as well as prolong the natural resolution process.^3,^26,^27,³⁷ When all functional causes have been excluded, of particular concern is any reported change in the intensity, quality, and location of the pain sensation and the persistence or dissemination of focal edema, color changes, and thermoregulatory adaptations that are seen initially as part of the acute pain dystrophic response.

It has been well established both clinically and experimentally that the sympathetic nervous system can contribute to the pathogenesis of RSD and other related pain syndromes.^2,^10,^11,^77,^78,^130,¹³¹ Evidence for this has been demonstrated by the fact that regional anesthetic blockade or interruption of the sympathetic nervous system produces relief of the pain of RSD and that electrical stimulation of the sympathetic chain exacerbates the pain in many patients suspected of having a sympathetically maintained pain.³⁷ Further evidence that the sympathetic nervous system contribution to the genesis and maintenance of certain abnormal pain syndromes is indeed a pathologic process is demonstrated by the observation that in normal persons when sympathetic outflow is electrically stimulated, no painful sensation is produced, nor does regional sympathetic blockade alter normal pain sensation.³⁷ Despite these and other clinical and experimental observations, there as yet exists no definitive laboratory model that explains fully how the sympathetic nervous system alters, produces, or maintains the pain of RSD and related disorders, although numerous plausible hypotheses have been proposed.^1,^2,^33,^67,^77,^101,^111,^114,¹²⁷ Collectively, these hypotheses can be grouped into either adaptive central nervous system dysfunction processes or peripheral end organ and receptor abnormalities.¹³

CLASSIFICATION

Several classification schemes for RSD have been described in the literature.^1,⁷⁴ In general terms, the more accepted classification schemes have been based on either the natural history of signs and symptoms of the disorder or on the type and magnitude of the precipitating injury.⁷¹^–⁷⁴ ¹⁰³ Lankford’s classification, based on injury type, proposes two distinct forms of sympathetic dysfunction (Box 81-2). The first, causalgia, results from direct nerve injury and is further subcategorized into either major or minor causalgia depending on whether the injury is due to a mixed motor/sensory or a sensory nerve, respectively. Traumatic dystrophy, the second type, is similarly subcategorized into major and minor subtypes. A minor traumatic dystrophy generally results from a less severe injury such as a sprain or contusion, whereas a major traumatic dystrophy results from a more extensive injury such as a fracture.^3,^34,^73,⁷⁴ Amadio and others have pointed out that the use of this type of classification scheme can be both confusing and imprecise, because some examples of RSD have no clear traumatic etiology and some minor causalgia may prove to be more disabling than a major causalgia.³

The second type of classification scheme for RSD is based on the natural history of the clinically observed physiologic, morphologic, and functional changes observed in untreated RSD.^115,¹²⁸ The Steinbrocker classification recognizes three distinct stages: (1) the acute stage (0 to 3 months), (2) the dystrophic stage (3 to 6 months), and (3) the atrophic stage (6 months and beyond) (Table 81-1).¹²⁸ In the earlier phases, the pain is often burning and more focal than diffuse, and the associated edema, vasomotor, and thermoregulatory dysfunction are usually prevalent. In the later stages, the pain is more constant and poorly localized. Muscle atrophy, joint stiffness, or contractures may develop, along with subcutaneous fibromatous organization and cyanosis of the skin. End-stage RSD is characterized by the appearance of more permanent changes of the skin, blood vessels, and joints (ankylosis).^37,¹¹⁵ It is important to recognize that RSD is a dynamic process, and although the previously mentioned stages accurately describe the symptomatic and pathophysiologic changes in general, in any individual a considerable temporal variability may occur in the development of the characteristic signs and symptoms, and subtle and partial manifestations are generally the rule rather than the exception. Therefore, no classification scheme is wholly satisfactory.^3,³⁷ In view of this, recently (similar to Dobyns) Boas⁸ has recognized the importance of a clinically descriptive classification scheme, and the term has been proposed and is gaining wider acceptance in the literature (Box 81-3).

TABLE 81-1 Classification of Reflex Sympathetic Dystrophy by Temporal Factors (Steinbrocker)

Type	Duration (months)
Acute	<3
Dystrophic	3–6
Atrophic	>6

BOX 81-3 Complex Regional Pain Syndrome

Type I	Reflex sympathetic dystrophy
Type I	Abnormal pain, dysfunction of the extremity, autonomic nervous system abnormalitites, and recognizable dystrophic clinical features without direct nerve injury
Type II	Causalgia
Type II	Abnormal pain, dysfunction of the extremity, autonomic nervous system abnormalities, and recognizable dystrophic clinical features with a known nerve injury?
Type III	Other pain dysfunction syndromes

PSYCHOLOGY OF PAIN AND DYSFUNCTION

In the previous section, the sensorineural mechanisms involved in the sensation of acute pain were outlined. These mechanisms, however, do not exist in isolation. The perception of a painful stimulus always yields an affective or emotional component that is individually variable and complex.^27,^29,⁵⁰ In the treatment of patients with PDS, the psychological component of the disorder may be pronounced and may evolve into the dominant clinical feature.²⁹

The Psyche

Although it is beyond the scope of this chapter to discuss at length the multiple theories of how the psyche may produce changes on the soma, in the past, considerable clinical emphasis has been placed on the probability that there are definite psychogenic causes for some chronic pain disorders, particularly RSD.^* Supporting the notion of a psychogenic basis for these disorders (even in less overt PDS) is that commonly a considerable disparity exists between the physical examination and the patient’s degree of fear, anxiety, and the reported degree of discomfort.^37,^50,^51,¹¹⁸ In the past, patients were variously described as “hysterical,” “emotionally labile,” “dependent,” “unstable,” “depressed,” and having “vulnerable, brittle autonomic nervous systems.”^24,^30,^58,^71,^95,⁹⁹ Such descriptive psychological assessments imply that a premorbid personality or even psychoses may exist. What is clear from review of these early accounts is that these psychological assessments were largely the result of opinion rather than based on psychological testing.^50,^88,¹²⁶ Several studies on RSD and other chronic pain syndromes, however, convincingly conclude that the observed personality and behavior changes are likely the consequence of the state of prolonged suffering rather than a manifestation of a pre-existing personality or psychological disorder.^50,^118,^120,^126,^129,¹³⁹ This is not to imply that some understandable emotional and psychological disturbances can occur in any individual living with chronic pain.^29,³² ^,37 ^,41 ^,50 Most frequently reported are persistent anxiety, reactive depression, dependency, and somatic preoccupation, all of which can impede the resolution of a PDS.²⁹ ^,37

In the process of identifying the psychological components of a PDS, one must differentiate from certain bona fide psychopathologic syndromes that often have as common features decreased pain tolerance or increased pain susceptibility or both; these are somatization disorder, conversion disorder, malingering, and factitious injury disorder.^3,^4,^29,^37,^38,⁴⁰ Patients with a somatization disorder often present with chronic pain as well as a history of recurrent multiple somatic complaints (at least 12) of long duration but for which no physical diagnosable disorder can be found.^4,^37,³⁸ These patients are convinced that they are seriously ill and are not deterred by the evidence of normal test results. The disorder is generally more common in women and usually begins during adolescence. Common complaints are chronic pain and weakness of the extremities, nausea, amnesia, shortness of breath, and fainting spells.^3,^4,³⁸

Conversion disorder, formerly called hysterical neurosis, like somatization disorder is also more common in women and usually presents with a history of chronic intermittent pain, the source of which is not medically identifiable.^4,³⁸ Other common symptoms are pseudoparalysis, nonanatomic sensory loss, and blindness.¹⁴⁵ Posturing of the hand and upper extremity is frequently observed, the persistence of which may result in contracture.^4,²⁹ Differing from somatization disorder, the onset of a conversion disorder is usually more sudden and, when identifiable, the physical manifestations of the disorder occur unconsciously in reaction to a disturbing psychological conflict.^4,^29,³⁸

Other identifiable syndromes in which complaints of pain are commonly associated include major depression (endogenous depression), hypochondriasis, factitious injury, and malingering.^4,³⁸ Major depression may be suspected by the characteristic dysphoric mood, sense of hopelessness, and vegetative symptoms (sleep alterations, poor appetite, fatigue), and often there is a preoccupation with pain, disease, and death.^4,^37,^38,^61,⁶² Hypochondriasis may be a symptom of major depression or may exist as a separate disorder characterized by a pervasive conviction that various imagined symptoms including pain are indicative of impending disease.^3,^4,^38,^61,⁶² Malingering is the conscious willful act of misrepresentation of symptoms of illness to avoid obligation or is contrived for secondary monetary gain. Factitious injury when secondary gain is identifiable represents a form of malingering.^3,⁴