Special problems
The early detection of depression is much more complex and challenging than the detection of other conditions seen in the primary care physician’s office. Perhaps the most significant reason for this is how the natural history of depression differs from that of most conditions for which there are effective measures for prevention or early detection. The successful early detection of diseases or of patients at risk for adverse events has generally involved conditions that follow a continuous or progressive course and are detectable in the presymptomatic phase. Examples are cervical cancer (the Papanicolaou smear), breast cancer (clinical breast examination and mammography) and hypertension (screening for elevated blood pressure). The natural history of depression is not one of a continuous, unresolving disorder with a defined and detectable presymptomatic phase. In many cases the depression progresses continuously, becomes severe and is readily detected clinically. However, in some cases of mild and, indeed, more severe depression patients improve without specific intervention (or even recognition).
A second problem relates to the role that symptoms play in depression. The goal of early detection is to identify disorders in the presymptomatic stage. This is usually most successful when the condition has a relatively long presymptomatic stage, there are good objective confirmatory diagnostic tests and the symptoms often occur only at an advanced stage. In a sense depression has none of these three characteristics. It is diagnosed essentially on clinical grounds, the early stages are associated with symptoms (often nonspecific), and the “presymptomatic” stage (even if there is one) is not necessarily prolonged, at least relative to other conditions. Since many early symptoms of depression also occur in other conditions (both physical and psychologic) the early detection of depression becomes even more complicated. Therefore, the development of an effective, accurate instrument is extremely difficult.
As Canada becomes increasingly multicultural additional problems arise concerning the use of early detection tests. During their development most instruments are not evaluated across a variety of cultures. Because the presentation of depression and the significance of associated symptoms can vary between cultural groups the routine use of early detection instruments may be difficult for physicians who care for people of different cultural and ethnic backgrounds.
Finally, several problems remain with the detection instruments themselves. Few of those that have been more carefully developed are specific for depression. Those that do focus on depression often have important development and testing shortcomings. Several instruments have been designed to detect the early stages of psychologic distress but are not diagnostically specific for depression or do not assess its severity. In addition, with some instruments the patients’ responses cannot easily be synthesized into a clinically useful score. Many tests do not achieve the sensitivity and specificity required to be considered successful.
Conclusions
From the primary care physician’s point of view the current situation is relatively clear-cut, though far from ideal. The available evidence does not support routine screening for the early detection of depression. In fact, studies that have evaluated the effectiveness of screening instruments in clinical practice tend to argue against their use at present. None the less, depression is an extremely important and common condition and deserves careful attention from primary care clinicians. The literature indicates that important episodes of depression are being missed. Hence, the problem is far from resolved.
Future directions
Clinicians must continue to be sensitive to and aware of the early stages of depression and carefully pursue their suspicions. Further research and development is required before the widespread routine use of even the best test can be recommended as part of the periodic health examination. Work is required in instrument development, particularly in light of the natural history of depression. Other avenues and approaches to early detection must be explored. Possibly the most useful approach would be a simple “diagnostic” test physicians could use in the office if they are concerned that a patient is in the early stages of depression. This may be more efficient than routine testing of all patients. Further work to improve the identification of people at high risk should have considerable benefit as well. Because early detection instruments may have some value in the elderly population more studies to evaluate early detection and subsequent management in this age group may prove valuable.
Résumé
(French Language)
La morbidité estimative de la dépression dans l’ensemble de la population va de 3,5% à 27%. Cette maladie très pénible amène souvent le suicide. Le traitement est efficace dans la plupart des cas; cependant de graves épisodes dépressifs échappent au diagnostic. Afin de savoir si la visite médicale périodique devrait comporter la recherche systématique des symptômes précoces de dépression nous retraçons dans MEDLINE et Science Citation Index les études comparatives aléatoires de l’usage de questionnaires à cette fin. Nous retenons sept outils qui répondent à nos critères de qualité: le Beck Dépression Inventory, la Center for Epidemiologic Studies Dépression Scale, la Zung Self-Assessment Dépression Scale, le Gêneral Health Questionnaire, la Hopkins Symptom Checklist, le Mental Health Inventory et la Hospital Anxiety and Dépression Scale. Les quatre essais comparatifs aléatoires ne militent pas suffisamment pour le dépistage systématique. Le diagnostic précoce de la dépression est difficile vu le génie évolutif de la maladie, la variabilité de sa symptomatologie, la diversité culturelle du Canada et l’insuffisance des outils de dépistage. Si le médecin de première ligne doit être à l’affût de la dépression on ne peut lui recommander à cette fin l’emploi d’outils de dépistage qui ne seraient pas plus perfectionnés et fondés sur de meilleurs travaux de recherche que ceux dont on dispose actuellement.