January 2010
Reviewer: Jeff C. Huffman, MD
Psychobehavioral predictors of somatoform disorders in patients with suspected allergies
Background: Current diagnostic criteria/models for somatoform disorders (SFD) are generally composed of a list of somatic symptoms plus exclusion criteria (e.g., "lacking objective signs of illness"). These descriptions do not include any positive or inclusion symptoms in the "psychobehavioral" domain, such as illness conviction or perceived locus of control, though such criteria could substantially help clinicians to ascertain the presence of one of these disorders in a given patient.
Methods: The authors performed a prospective trial to correlate "psychobehavioral" characteristics with the presence of a SFD among patients who were admitted to a hospital for workup of suspected allergies (a population selected because it has a high rate of medically unexplained symptoms and the work-up for such a condition is extensive). Subjects admitted to the hospital for such a workup were approached for enrollment, and underwent (1) SCID interviews for SFD, (2) self-rated questionnaires on illness perception, disease conviction, illness behavior, health attitudes, reassurability in the medical setting, and health attitudes, and (3) additonal standard evaluations for somatization, depression, and anxiety disorders using the Patient Health Questionnaire. Upon completion of the medical workup, the lead physician in the patient’s care was asked to assert (on a 0 to 4 scale) the degree to which the patient’s workup for allergies had revealed objective disease.
Results: 215 (nearly 90% of the admitted patients over the enrollment period) consented to participation. A comparison group (N=50) consisting of patients with known allergies was also included. The vast majority completed both the interviews and self-report measures. 22.0% of work-up subjects had SFD; such patients were vastly more likely to have blinded clinicians rate their presenting symptoms as not explained by an organic etiology after completion of an extensive medical workup (75% vs. 17% in non-SFD group; p<0.001). Patients with SFD also had significantly greater scores on PHQ somatization, depression, and anxiety scales (p<0.001 on all). Regarding psychobehavioral variables, SFD patients had substantially higher scale/subscale scores in a variety of domains related to illness perception, disease conviction, illness behavior, health attitudes, reassurability in the medical setting, and health attitudes. A final predictive model of SFD combining psychobehavioral variables utilized (1) disease conviction, (2) reduced readiness to self-scan own body for symptoms, (3) decreased internal locus of control, and (4) dissatisfaction with care as the four components of a model that was able to correctly classify 90% of SFD and 88% of non-SFD cases.
Discussion: This was a carefully-performed and very interesting investigation of an understudied topic. Certainly there are some caveats regarding this study’s results. First, one would need to confirm the results in a different population compared to the (rather unusual) population of patients admitted for a full workup of allergies. Second, the multiple statistical tests performed on the many scales and subscales collected in this study is a technical limitation (if you run enough tests, you’ll find a ‘significant’ difference somewhere)—though to be fair the authors’ findings both had face validity and the differences were often vast (usually p<0.001). Finally, one could argue that patient’s who have long-undiscovered real disease would likely feel dissatisfied, have a sense that something was really wrong, and would have a limited sense of control.
However, the authors’ findings do ring very true to the clinical presentation of SFD patients—the variables that seem most valid are the strong disease conviction, external locus of control, and dissatisfaction with care. Furthermore, the ability to potentially add to existing SFD criteria some specific and clinically-meaningful characteristics of patients with SFD will be tremendously valuable in better defining and studying these disorders. One suspects that these models of psychobehavioral predictors will become even more finely honed in future studies, but these results are already useful and interesting. Of note, though the SFD patients did have higher anxiety and depression scores, these scores were not high enough to suggest that most SFD patients had an active anxiety or depressive disorder that accounted for their symptoms (for example, the mean PHQ-9 score was around eight, under the cutoff for a depressive disorder, despite the fact that it contains multiple somatic symptoms).