Recognizing Somatization Disorder and Undifferentiated Somatoform Disorder as Diagnostic Possibilities
The diagnoses of somatization disorder and undifferentiated somatoform disorder are often missed in patients. To make a correct diagnosis, the diagnostician first must be willing to consider that either of these disorders could be a possibility. In determining the prevalence of these disorders, three separate populations should be considered: the general population, patients seen in primary care and general hospitals, and patients being treated in the specialty care sector.

Somatization Disorder
Somatization disorder is relatively rare in the general population, according to the results of the Epidemiologic Catchment Area (ECA) study. ECA investigators estimated that 0.13% of the general population - or about 1 person in every 1,000 - had somatization disorder. ECA investigators at Duke University, Durham, North Carolina, used a somewhat different methodology from that used at the other ECA sites and found the prevalence of the disorder in the Piedmont region of North Carolina to be approximately 0.4%. Previous estimates were in the range of 0.4%-2.0% of the population. However, these estimates from the ECA data likely underestimate the true prevalence of somatization disorder because of the limitations of the Diagnostic Interview Schedule, the instrument used to make the diagnoses in the ECA study.

Patients with somatization disorder tend to congregate in primary care and general hospital settings because they perceive themselves to be very ill, with multiple unexplained somatic complaints. Such patients frequently seek out health care providers. Estimates of the prevalence of somatization disorder among patients seen in primary care settings range from as low as 0.2% for young women ages 16-25 to as high as 6% of all patients seen in family practice or primary care settings. If the 6% figure reflects the prevalence in the general population, 2-3 of the 50 patients generally seen in primary care settings each day probably have somatization disorder. This estimate means that somatization disorder falls within the prevalence estimates for common disorders such as diabetes mellitus and urinary tract infections.

Equally high rates are reported for patients in general hospital settings. Cott (1986) estimated that 1 in 50 women admitted to a medical ward had somatization disorder. Both Woodruff (1967) and deGruy et al. (1987b) reported that 9% of the patients admitted to the medical-surgical services of general hospitals had somatization disorder. Clearly, these data indicate that somatization disorder is prevalent in primary care and general hospital settings and should be considered as a diagnostic possibility.

In the specialty care sector, patients with somatization disorder are also overrepresented. Estimates of the prevalence of somatization disorder in patients with conditions such as irritable bowel syndrome, polycystic ovary disease, and chronic pain range from 12% to as high as 28%. Similarly, women receiving non-cancer-related hysterectomies had a 27% prevalence of somatization disorder. Folks et al. (1984) found that patients with conversion symptoms had a high probability - 34% - of having somatization disorder. Katon et al. (1984) found that 6% of the patients seen in a consultation service of a teaching hospital had somatization disorder.

In psychiatric practices, somatization disorder may be both underrepresented and unrecognized. Slavney and Teitelbaum (1985) reported that 8% of the patients who were referred for psychiatric consultation with medically unexplained symptoms had somatization disorder. Prevalence rates of somatization disorder in psychiatric settings have varied widely in several small studies.

Undifferentiated Somatoform Disorder
Most of the data relating to undifferentiated somatoform disorder concern patients who are variously described as “somatizers” or patients who have somatization syndrome. The operational definition of undifferentiated somatoform disorder used for research purposes requires that 6-12 (4-12 for men) of the somatization disorder symptoms listed in DSM-III-R (American Psychiatric Association 1987) be present. Patients who somatize are only a subset of patients with undifferentiated somatoform disorder and, therefore, represent a prevalence that is lower than the total population of individuals with this disorder.

The first reported prevalence of somatizing individuals in the general population was from the Los Angeles site of the ECA study, for which a 4.4% lifetime prevalence was noted. Across all sites of the ECA study, the prevalence of patients who somatized was 11.6% of the general population.

In primary care and general hospital settings, patients who somatize are more prevalent than in the general population. Two family medicine clinics in Montreal found a prevalence of 16.6% among their patients, whereas a more recent study of Danish primary care patients found a prevalence of between 5.7% and 27.0%, depending on the diagnostic criteria used.

Convincing data concerning the prevalence of undifferentiated somatoform disorder in the specialty care sector have not been reported. However, clinical wisdom indicates that a high prevalence of undifferentiated somatoform disorder is seen in internal medicine and surgical specialty practices.