Annotations by Anna Dickerman, MD and Michael Sharpe, MD, FAPM
ANNOTATION (Dickerman & Sharpe)
The Finding: The authors evaluated the diagnostic sensitivity and specificity of a commonly used and well-validated self-rated symptom questionnaire, the Patient Health Questionnaire (PHQ15), in identifying patients with medically unexplained somatic symptoms. Despite the fact that such symptom rating scales are being increasingly used because of assumed cost- and time-effectiveness, this study found that the scale was not a useful way to do that and advocated a standard medical assessment.
Strength and Weaknesses: Strengths of the study include its large and representative group of neurology patients in Scotland, UK. These patients received a full specialist diagnostic assessment as well as symptom assessment using the study measures. A limitation of the study is its geographical confinement to Scotland. Also, the study was performed in secondary care, whereas the measure being evaluated (PHQ15) was developed for primary care. It may be that patients attending neurology clinics have specific individual characteristics that pose diagnostic challenges and thus may limit the generalizability of the study’s findings to other patient populations.
Relevance: The characteristic of having multiple self-reported somatic complaints has previously been recommended as a helpful diagnostic clue for identifying patients with medically unexplained symptoms (Stone et al, 2005). This has led to more widespread use of self-rating symptom scales as a quick and inexpensive means of diagnosing these patients. This study confirms the common clinical assumption that patients with symptoms unexplained by disease report more symptoms. However, in this study, self-reported symptom counts actually did not perform well on an individual level to identify patients with medically unexplained symptoms and thus may not be useful as a diagnostic tool.
Objective: Somatic symptoms unexplained by disease are common in all medical settings. The process of identifying such patients requires a clinical assessment often supported by clinical tests. Such assessments are time-consuming and expensive. Consequently the observation that such patients tend to report a greater number of symptom has led to the use of self-rated somatic symptom counts as a simpler and cheaper diagnostic aid and proxy measure for epidemiological surveys. However, despite their increasing popularity there is little evidence to support their validity.
Methods: We tested the score on a commonly used self-rated symptom questionnaire- the Patient Health Questionnaire (PHQ 15) (plus enhanced iterations including an additional 10 items on specific neurological symptoms and an additional 5 items on mental state) for diagnostic sensitivity and specificity against a medical assessment (with 18 months follow-up) in a prospective cohort study of 3781 newly attending patients at neurology clinics in Scotland, UK.
Results: We found 1144/3781 new outpatients had symptoms that were unexplained by disease. The patients with symptoms unexplained by disease reported higher symptoms count scores (PHQ 15: 5.6 (95% CI 5.4 to 5.8) vs 4.2 (4.1 to 4.4) p<0.0001). However, the PHQ15 performed little better than chance in its ability to identify patients with symptoms unexplained by disease. The findings with the enhanced scales were similar.
Conclusions: Self-rated symptom count scores should not be used to identify patients with symptoms unexplained by disease.