Depression in adults

Depression can describe both a mood and an illness.

Major depressive disorder is a clinical syndrome involving mood, neurovegetative functions, cognition, and behaviour.

Depressive disorders are very common and are among the leading causes of disability and excess mortality worldwide.

Risk factors include prior depression and a family history of depression. A history of adverse childhood experiences, recent bereavement, stress, or medical illness may contribute.

For screening and diagnosis, self-rating forms are helpful, but clinical diagnosis is essential. Positive screening should trigger full history, mental status examination, treatment, and follow-up.

Most patients respond well to treatment with medication, psychological therapy, or a combination of both. Watchful waiting may be a suitable approach for some people with milder symptoms. Treatment is personalised, and takes into account patient choice, previous treatment history, treatment availability, severity of depressive symptoms, and psychiatric comorbidities.

Suicidal ideation can occur before and peak during treatment, so early and careful follow-up is advised.

Depressive disorders are typically characterised by persistent low mood, loss of interest and enjoyment, neurovegetative disturbance, and reduced energy, causing varying levels of social and occupational dysfunction. Depressive symptoms include depressed mood, anhedonia, weight changes, libido changes, sleep disturbance, psychomotor problems, low energy, excessive guilt, poor concentration, and suicidal ideation. In some cases the mood is not sad, but anxious or irritable or flat.[1]American Psychiatric Association. Diagnostic and statistical manual of mental disorders, 5th ed., text revision (DSM-5-TR). Washington, DC: American Psychiatric Publishing; 2022.

Both International Classification of Diseases (ICD)-11 and Diagnostic and statistical manual of mental disorders, fifth edition, text revision (DSM-5-TR) define ‘mild’, ‘moderate’, and ‘severe’ depression based on the number and intensity of symptoms, and on the degree of functional impairment.[1]American Psychiatric Association. Diagnostic and statistical manual of mental disorders, 5th ed., text revision (DSM-5-TR). Washington, DC: American Psychiatric Publishing; 2022.[2]World Health Organization. ICD-11 for mortality and morbidity statistics. Jan 2024 [internet publication]. https://icd.who.int/browse/2024-01/mms/en ​​​ However within clinical practice as well as within clinical trials, there is variability in how different levels of severity of depression are defined.[3]Zimmerman M, Morgan TA, Stanton K. The severity of psychiatric disorders. World Psychiatry. 2018 Oct;17(3):258-75. https://onlinelibrary.wiley.com/doi/10.1002/wps.20569 http://www.ncbi.nlm.nih.gov/pubmed/30192110?tool=bestpractice.com ​ Globally, the most widely used tool for assessing severity of depression in clinical practice is the 9-item version of the Patient Health Questionnaire (PHQ-9), which is based on DSM criteria; scores may be used to characterise severity of depression, and to assess treatment response.​[4]Kroenke K, Spitzer RL, Williams JB. The PHQ-9: validity of a brief depression severity measure. J Gen Intern Med. 2001 Sep;16(9):606-13. http://www.ncbi.nlm.nih.gov/pubmed/11556941?tool=bestpractice.com

There is no subthreshold (minor) depression diagnosis in DSM-5-TR, but the label has sometimes been applied to diagnose a patient with two to four depressive symptoms, including depressed mood or anhedonia, lasting longer than 2 weeks.[5]Kessler RC, Zhao S, Blazer DG, et al. Prevalence, correlates, and course of minor depression and major depression in the National Comorbidity Survey. J Affect Disord. 1997 Aug;45(1-2):19-30. http://www.ncbi.nlm.nih.gov/pubmed/9268772?tool=bestpractice.com [6]Kendler KS, Gardner CO Jr. Boundaries of major depression: an evaluation of DSM-IV criteria. Am J Psychiatry. 1998 Feb;155(2):172-7. https://psychiatryonline.org/doi/10.1176/ajp.155.2.172 http://www.ncbi.nlm.nih.gov/pubmed/9464194?tool=bestpractice.com

Persistent depressive disorder (termed ‘dysthymic disorder’ within ICD-11) is characterised by at least 2 years of a depressed mood for most of the day, for more days than not, for at least 2 years.[1]American Psychiatric Association. Diagnostic and statistical manual of mental disorders, 5th ed., text revision (DSM-5-TR). Washington, DC: American Psychiatric Publishing; 2022.[2]World Health Organization. ICD-11 for mortality and morbidity statistics. Jan 2024 [internet publication]. https://icd.who.int/browse/2024-01/mms/en See Persistent depressive disorder.