Synopsis
Recognise recurrent seasonal pattern and chronic depressive course through longitudinal evidence, exclude bipolar, sleep and physical causes, treat current severity using established depression care and build prevention around predictable timing and residual impairment.
- A seasonal pattern requires repeated temporal relationship between depressive episodes and a particular season, with remission or marked change outside that period; one difficult winter is insufficient.
- Map several years of mood, sleep, appetite, energy, function, treatment and activation against seasons, work patterns, anniversaries and social changes.
- Assess current severity, psychosis, suicide, function and dependants exactly as for other depression and do not wait for daylight or season to change.
- Screen bipolarity, especially opposite-season activation, reduced sleep need and antidepressant or light-related mood elevation.
- Persistent depressive illness involves a chronic low-mood course with ongoing cognitive, biological and functional effects, sometimes with superimposed major episodes.
- Exclude or treat thyroid disease, sleep disorder, pain, substances, medicines and social adversity according to history and examination.
- Use established psychological and antidepressant options for current severity and preference; chronicity may require rehabilitation and specialist review rather than therapeutic pessimism.
- Evidence for light therapy is uncertain; discuss quality, UV filtering, timing, adverse effects and clinical review rather than presenting a commercial lamp as established replacement care.
- Begin relapse-prevention work before the person's usual season where the pattern is established, using warning signs, routines, treatment access and a plan for rapid escalation.
Key red flags
Seasonally recurrent depression can still become severe, psychotic or suicidal and needs the same immediate risk formulation as non-seasonal episodes.
Spring or summer activation, reduced sleep need, episodic overspending or antidepressant-induced elevation suggests a bipolar seasonal course rather than unipolar depression.
Persistent fatigue and hypersomnia require assessment for sleep apnoea, thyroid disease, anaemia, pain, medicines and substance use rather than automatic seasonal attribution.
Longstanding low mood can normalise major functional impairment, self-neglect and abuse in both patient and clinician accounts.
Light boxes can cause headache, eye strain, insomnia or activation and need caution with eye disease, photosensitising medicines and bipolar vulnerability.
Investigation priorities
Establish repeated onset, remission, severity, treatment response and alternative recurring explanations.
Verify adequacy, adverse effects, preferred options, seasonal timing and previous relapse signals.
Management branches
Depressive symptoms appear to recur or worsen seasonally.
- Map several years of episodes, remission, function, treatment, sleep, work, social events and opposite-season activation.
- Assess current depression, suicide, psychosis and dependants and investigate bipolar, sleep and physical alternatives.
- Communicate whether seasonality is established, possible or unconfirmed and treat current needs without waiting for further cycles.