Dr Steven King provided an interesting summary of complex regional pain syndrome (CRPS) in Psychiatric Times ("Complex Regional Pain Syndrome," June 2006, page 9). We felt it would be useful to provide some additional observations on the relationship between CRPS type I and psychological causes of pain. The diagnosis of CRPS type I is based on 4 criteria1: (1) a noxious event; (2) subjective symptoms of pain, etc, disproportionate to this event; (3) objective physical changes; and (4) absence of other causes (including psychological).
The difficulty we want to draw attention to relates primarily to the use of "physical disproportionality" in the diagnostic criteria of an ostensible physical condition. Studies of reflex sympathetic dystrophy, the predecessor of CRPS type I, show a high incidence of comorbid depression, anxiety, and posttraumatic stress disorder2,3; it is important that clinicians be vigilant because persons with symptoms disproportionate to a physical cause may in fact have either CRPS type I or one of the previously mentioned mental illnesses.
This not only makes the diagnosis of CRPS type I somewhat anomalous in that it effectively becomes a physical condition requiring a psychiatric assessment for diagnosis, but, as Dr King's reference to malingering reminds us, that the psychiatrist's job of deciding what proportion of a physically disproportionate pain is also disproportionate to mental illness is highly problematic. One might accept that it is possible to assess the severity of a familiar mental illness like depression and translate this to yield a proportionate relative etiologic contribution in a given pain presentation.
However, the difficulties do not end there because DSM-IV also includes a specific category of mental illness called "pain disorder," which—like CRPS type I—also involves pain that cannot be explained fully by a physiologic process or a physical disorder.4 Pain disorder was effectively introduced to capture cases in which pain is disproportionate to both physical factors and familiar mental illnesses. CRPS type I diagnostic criteria rely on excluding a diagnosis of pain disorder by criterion 4; however, there is the very real question of how to distinguish the 2 causes of "doubly" disproportionate pain from each other in practice.
DSM-IV maintains that pain disorder should be diagnosed only if "psychological factors are judged to have an important role in the onset, severity, exacerbation, or maintenance of the pain."4 Unfortunately, the utility of this depends first on the clinician's ability to distinguish psychological factors that are the cause of pain from those that are a consequence of it, and second, on adequately resolving the question of "proportionality" in relation to notoriously difficult to define emotional and other factors.
The literature on CRPS type I does not really address these issues, but therapy guidelines indicate that psychological factors may be important when pain has lasted for 2 months or more.5 This stipulative use of temporal factors to decide between physical (CRPS type I) and psychological (implicitly somatoform) causes of pain is effectively forced on us by the aforementioned intractable problems of identifying and then deciding causality and proportionality in relation to psychological factors. Not surprisingly, this is inherently problematic. In particular, it is difficult to understand why the presumed physical factors causing CRPS type I—the nature of which is by definition unknown—cannot operate beyond 2 months, or indeed why the diagnosis of pain disorder should be implicitly dependent on a temporal criterion not mentioned in DSM-IV. The crucial point, however, is that without a nontemporal, and therefore, nonarbitrary way of distinguishing pain due to CRPS type I from that due to pain disorder, the possibility will always remain open that pain attributed to the former is in fact caused by the latter.
It is tempting to think that objective changes covered by criterion 3 will help. The difficulty here, however, is that the immobilization of a limb for whatever reason can itself lead to these changes.6,7 This indicates that, strictly speaking, the only circumstances in which objective changes can be used to differentiate CRPS type I from cases of pain disorder are those in which immobilization has not occurred. To restrict the diagnosis of CRPS type I to these extremely rare cases would clearly make it virtually useless. This, coupled with the realization that the psychological causes of immobilization that present the most challenging problem (ie, factitious disorder and malingering8,9) do not even involve pain, illustrates that introducing a set of diagnostic criteria for a medically unexplained condition like CRPS type I is a good deal less problematic than applying them in practice.
Dr Turner is a consultant psychiatrist at the Bamburgh Clinic, St Nicholas Hospital, in Newcastle upon Tyne, United Kingdom. Dr Neal is a consultant psychiatrist at the Bristol Priory Hospital in Bristol, United Kingdom.
