Disorders of the mood are often called affective disorders, since affect is the external display of mood or emotion which is, however, felt internally. Mood disorders are defined as mixtures of symptoms packaged into syndromes. These syndromes are consensus statements from committees writing the nosologies of psychiatric disorders for the Diagnostic and Statistical Manual of Mental Disorders (DSM) of the American Psychiatric Association (Table 1).
Diagnosis both in clinical practice and in clinical research studies is based on these sets of specific signs and symptoms. These criteria have helped distinguish various mood disorders that may have different causes and that certainly require different clinical management. The most common and readily recognised mood disorder is major depression as a single episode or recurrent episodes. Dysthymia is a less severe but often longer-lasting form of depression, i.e. over two years in duration and often unremitting. Another type of mood disorder is bipolar disease, which is characterised by the occurrence of manic episodes besides depression.
There are no pathognomonic markers of depression, although this is an area of active research (Duffy A., 2000, Can. J. Psychiatr., 45:340-348).
TABLE 1Diagnostic criteria for major depressive disorder*A.The patient has depressed mood (e.g., sad or empty feeling) or lossof interest or pleasure most of the time for 2 or more weeks plus 4or more of the following symptomsSleepInsomnia or hypersomnia nearly every dayInterestMarkedly diminished interest or pleasure innearly all activities most of the timeGuiltExcessive or inappropriate feelings of guiltor worthlessness most of the timeEnergyLoss of energy or fatigue most of the timeConcentrationDiminished ability to think or concentrate;indecisiveness most of the timeAppetiteIncrease or decrease in appetitePsychomotorObserved psychomotor agitation/retardationSuicideRecurrent thoughts of death/suicidal ideationB.The symptoms do not meet criteria for a mixed episode (majordepressive episode and manic episode)C.The symptoms cause clinically significant distress or impairment insocial, occupational, or other important areas of functioningD.The symptoms are not due to the direct physiological effects of asubstance (e.g., a drug of abuse, a medication) or a general medicalconditionE.The symptoms are not better accounted for by bereavement*Adapted from the Diagnostic and Statistical Manual of Mental Disorders, 4th editon.’
Depressive disorders are associated with poor work productivity, as indicated by a 3-fold increase in the number of sick days in the month preceding the illness for workers with a depressive illness compared with coworkers who did not have such an illness (Parikh, S. V. et al., 1996, J. Affect. Disord. 38:57-65; Kessler, R. C. et al., 1999, Health Aff. 18:163-171).
Depressive illnesses also affect family members and caregivers (Denihan, A. et al., 1998, Int. J. Geriatr. Psychiatr. 13:691-694), and there is increasing evidence that children of women with depression have increased rates of problems in school and with behaviour, and have lower levels of social competence and self-esteem than their classmates with mothers who do not have depression (Goodman, S. H. and Gotlib, I. H., 1999, Psychol. Rev. 106:458-490). Depression is the leading cause of disability and premature death among people aged 18 to 44 years, and it is expected to be the second leading cause of disability for people of all ages by 2020 (Murray, C. J. and Lopez, A. D., 1997, The Lancet 349:1498-1504; Gredon, J. F., 2001, J. Clin. Psychiatr. 62:26-31).
Depressive illnesses have also been shown to be associated with increased rates of death and disability from cardiovascular disease (e.g. Pratt, L. A. et al., 1996, Circulation 94:3123-3129, Bush, D. E. et al., 2001, Am. J. Cardiol. 88:337-341). Among 1551 study subjects without a history of heart disease who were followed for 13 years, the odds ratio for acute myocardial infarction among the subjects who had a major depressive episode was 4.5 times higher than among those who did not have a depressive episode. Among consecutive patients admitted to hospital with an acute myocardial infarction who had their mood measured with a standard depression rating scale, even those with minimal symptoms of depression had evidence of higher subsequent risk of death following their infarction and over the next 4 months. This risk was independent of other major risk factors, including age, ventricular ejection fraction and the presence of diabetes mellitus.
Surprisingly, for such a common disease there is little agreement on the association between age and onset. This is due to the fact that research is hampered by the absence of an unambiguous and universally agreed on set of diagnostic criteria and the fact that many of the studies have included patients already in the medical care system. It is well known that many people who meet the diagnostic criteria for depression do not seek treatment.
Despite its high prevalence, only one-third of all patients with depression receive adequate treatment (Judd, L. L. et al., 1996, Am. J. Psychiatry 153:1411-1417). The following are 4 common clinical errors that lead to diagnostic or treatment failures associated with depressive disorders:                Insufficient questioning. Diagnostic failures occur when the patient is not asked questions that may elicit the symptoms of a mood disorder despite what should be a high index of suspicion based on its prevalence. The mnemonic “SIGECAPS” (sleep, interest, guilt, energy, concentration, appetite, psychomotor, suicide) (Table 1) may be a useful clinical adjunct (i.e., 4 or more SIGECAPS for major depression, 2 or 3 SIGECAPS for dysthymia).        Failure to consult a family member. Owing to the cognitive distortions associated with the disease, it is not unusual for patients to minimize or exaggerate their symptoms. Thus, in patients who are relatively new to one's practice, it is risky at best to make (or exclude) a diagnosis of depression without collateral information from a relative, such as a spouse or parent.        Acceptance of a diagnosis of a mood disorder despite lack of diagnostic criteria (e.g., starting treatment for depression when only a “depressed mood” is present without the concomitant mental and physical symptoms [i.e., SIGECAPS]).        Exclusion of a diagnosis or failure to start treatment for depression despite the associated symptom complex (e.g., “Of course you're depressed. Who wouldn't be depressed if these events were occurring in their life?” In other words, “explaining” the diagnosis rather than considering treatment options).        
These clinical errors, coupled with the stigma associated with psychiatric conditions (Sirey, J. A. et al., 2001, Psychiatr. Serv. 52:1615-1620), result in the underdiagnosis of major mood disorders.
Another major hypothesis in the field of psychotherapy at present, is that recognition and treatment of both unipolar and bipolar depressions, causing all symptoms to remit for long periods of time, might prevent progression of the disease to more difficult states, emphasising that early recognition of mood disorder subtype is of great importance.
Taken all these data together, it is clear that there exists a major need for a reliable diagnosis of depression, or, alternatively, an assay that can confirm a diagnosis on basis of the SIGECAPS criteria.