Table 2 New strategies for deriving diagnostic categories and worked examples for major depression

1. Abandon the artificial distinction between brain (neurological) and psychiatric or psychological (mental) disorders

1. Focus clinical attention on the broad affective, cognitive, motor and sleep or circadian aspects of significant depressive disorders [58–61, 72, 106];

2. Encourage systematic cross-sectional and longitudinal structural brain imaging across the various phases of early- and late-onset depressive disorders [78, 83].

2. Avoid the use of single categorical states (for example, major depression, schizophrenia, bipolar disorder) that describe heterogeneous groups

Only use major depression in association with specific descriptors including early- versus late-onset, preceded by childhood anxiety; comorbid with alcohol or other substance misuse, significant circadian disturbance, psychotic features, significant psychomotor disturbance or other discrete melancholic features [61, 63–65, 78, 84, 107–110].

3. Promote pathways to illness models that have a strong basis in longitudinal epidemiology and related risk factor or neuroscience research

Promote categories such as depression preceded by childhood anxiety; childhood traumatic events; depression associated with significant circadian disturbance; depression associated with psychomotor change; depression following a clear manic episode [61].

4. Incorporate age-of-onset and stage-of-illness concepts into all diagnostic processes

1. For depression, the first age of a clear depressive syndrome would be recorded, as well as the first clear episode of sufficient severity to justify intervention [66, 111, 112];

2. For depression, the clear pattern of remission, relapse or recovery would be recorded for all patients [113].

5. Reduce the concept of comorbidity to the co-occurrence of genuinely independent conditions

1. Depression occurring in association with documented diabetes or cardiovascular disease [114–119];

2. Rejecting the notion of anxiety and depression representing comorbid conditions, as distinct from linked developmental phenotypes [61].

6. Place greater importance on the significance of response to specific treatments

1. Patients with anxiety and depression who fail to respond in the acute phase to CBT but do respond to an SSRI or SNRI can be considered to be in a different category [103, 104, 113];

2. Patients with psychomotor change or cognitive impairment who do not respond to SSRI or SNRI but do respond to physical treatments such as electroconvulsive therapy can be considered as a different category [64, 120];

3. Patients with sleep or circadian disturbance who fail to respond to respond to CBT or SSRI or SNRI but do respond to behavioral or pharmacological management that targets the circadian system can be considered to be in a different category [121–124].