Summary

• Not considered to be a unique diagnostic entity in itself, but rather a sub-type specifier used to describe temporal variations in recurrent major depressive or bipolar disorders over at least a 2-year period.
• Most commonly presents with onset of depression in the autumn or winter, and full remission of symptoms in the spring or summer.
• Atypical vegetative symptoms of depression are common, such as hypersomnia, hyperphagia, and weight gain.
• Assessment is based on self-report, clinical interview, and behavioural observation.
• Light therapy, SSRIs, and serotonin-noradrenaline (norepinephrine) re-uptake inhibitors (SNRIs), either alone or in combination, are considered the initial treatment options.
• Longer-term clinical management and monitoring are typically required. Light therapy and/or bupropion (extended release) may be used as prophylactic therapy.