Most common functional mental illness characterised by a pervasive lowering of mood, reduced enjoyment and negative patterns of thinking – may be experienced by up to 30% of the population during their lives. Assumed to be high incidence of underdiagnosis and undertreatment.

1) Unipolar – episode of depression only
Bipolar – tends to upswings and downswings of mood
2) Severe

Unclear. Family history can be positive. Neurochemical and neuroendocrine mechanisms may play a role. Monoamine hypothesis – suggests that depression is due to a functional deficiency of monoamine neurotransmitters (norepinephrine and serotonin). Adverse life events and circumstances increase risk. Some medications increase risk for depression – amphetamines, antineoplastic agents, Parkinsonism agents, barbiturates, benzodiazepines, digoxin

Clinical features:
Depressed mood, loss of pleasure or interest in usual activities, feelings of sadness, hopelessness, apathy, despair, lack of enjoyment from everyday activities, sleep pattern changes, withdrawal from friends, reduced appetite/weight loss, reduced libido, pessimistic thoughts about self, the world and the future, cognitive function may be impairs (reduced attention and/or concentration)

Differential diagnosis – normal sadness (eg bereavement)

• Risk assessment (eg for suicide, self-neglect
• Drugs (tricyclic antidepressants (TCA’s); selective serotonin reuptake inhibitors (SSRI’s); monoamine oxidase inhibitors (MAOI’s); lithium)
• ECT – electroconvulsive therapy (indicated for severely depressed; those at risk of starvation from loss of appetite; failure to respond to drugs)
• Psychotherapy (supportive)

Most single episodes last up to 8 months – 20% last up to 2 years; 50% have recurrences.
Poorer outcome is related to younger age of onset, severity of initial symptoms and the presence of co-morbidity (psychiatric or physical).

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