Revise Diagnostic criteria for mood (affective) disorders for Cambridge 9990 (1.2.1)

Affective disorders, also known as mood disorders, are a category of mental health conditions characterised by a significant disturbance in a person's emotional state or mood. This disturbance can manifest as extreme sadness, as seen in major depressive disorder (MDD), or as alternating periods of depression and mania, as in bipolar disorder. To ensure consistent and reliable diagnosis, clinicians use standardised classification systems. The two most prominent systems are the Diagnostic and Statistical Manual of Mental Disorders (DSM), currently in its fifth edition (DSM-5), published by the American Psychiatric Association, and the International Classification of Diseases (ICD), now in its eleventh revision (ICD-11), produced by the World Health Organisation. These manuals provide specific criteria, including symptoms and duration, that must be met for a diagnosis to be made.

According to DSM-5, a diagnosis of Major Depressive Disorder requires the individual to experience five or more specific symptoms during the same two-week period, representing a change from previous functioning. Crucially, at least one of the symptoms must be either (1) depressed mood or (2) loss of interest or pleasure (anhedonia). The other potential symptoms include significant weight loss or gain, insomnia or hypersomnia, psychomotor agitation or retardation, fatigue or loss of energy, feelings of worthlessness or excessive guilt, diminished ability to think or concentrate, and recurrent thoughts of death or suicide. These symptoms must cause clinically significant distress or impairment in social, occupational, or other important areas of functioning and must not be attributable to a substance or another medical condition.

To better understand the wide-ranging impact of MDD, its nine diagnostic symptoms can be grouped into four categories. Affective symptoms relate to mood and emotions, such as persistent sadness, feelings of worthlessness, and anhedonia. Behavioural symptoms are observable changes in action, including social withdrawal, psychomotor retardation (slowed movement), or agitation. Cognitive symptoms concern thought processes, like diminished concentration, indecisiveness, and recurrent thoughts of death. Finally, somatic (or physical) symptoms involve the body, such as significant changes in appetite or weight, sleep disturbances (insomnia or hypersomnia), and a profound loss of energy or fatigue. Recognising these categories helps to appreciate how depression is a whole-body illness, affecting more than just a person's mood.

Despite the structured criteria, diagnosing MDD faces several challenges. One issue is reliability; different clinicians may interpret a patient's self-reported symptoms differently, potentially leading to low inter-rater reliability. Validity is another concern. The high rate of comorbidity (co-occurrence) with other disorders, such as anxiety disorders, raises questions about whether MDD is always a distinct, separate condition. Furthermore, there is significant symptom overlap between MDD and other disorders, and even with 'normal' grief or sadness, creating diagnostic ambiguity. Cultural differences in expressing distress can also affect the validity of a diagnosis, as symptoms like fatigue may be emphasised over low mood in some cultures. The categorical 'all-or-nothing' approach of DSM-5 (you either have it or you don't) is also criticised for not capturing the dimensional nature of depression.