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Seasonal Affective Disorder (SAD)

BASICS

  • Definition: Mood episodes as part of major depressive or bipolar disorder that follow a seasonal pattern.
  • Typical Presentation: Depressive episodes most often begin in fall/winter, remit in spring/summer. Less commonly, spring-summer onset occurs.
  • Severity: Ranges from "winter blues" to disabling illness.

EPIDEMIOLOGY

  • Incidence: Up to 500,000 Americans affected each winter.
  • Prevalence: Up to 30% of primary care visits in winter report depressive symptoms.
  • Peak Age: 20s–30s, but can occur at any age.
  • Sex: Female > male (3:1).

ETIOLOGY & PATHOPHYSIOLOGY

  • Photoperiod/Circadian Hypothesis: Shorter daylight increases melatonin secretion → circadian phase shift → depression.
  • Serotonin Dysregulation: Altered serotonin clearance/secretion implicated; SSRIs effective.
  • Genetics: Family/twin studies; variants in melanopsin (OPN4), GPR50 melatonin receptor.
  • Other factors: Reduced vitamin D levels may contribute.

RISK FACTORS

  • Seasonality: Most common in January–February.
  • Environment: Working in windowless spaces; little sunlight exposure.

GENERAL PREVENTION

  • Light Therapy: Start at beginning of winter if prone to SAD.
  • Lifestyle: Maximize outdoor daylight exposure.
  • Medication: Bupropion is the only FDA-approved agent for prevention.
  • Possible Preventatives: Low-dose evening melatonin, though evidence is mixed.

COMMONLY ASSOCIATED CONDITIONS

  • Alcohol use disorder, ADHD, binge eating.

DIAGNOSIS

  • DSM-5: Add “with seasonal pattern” specifier to MDD, bipolar I, or II disorder.
  • Criteria:
  • Remission in nonseasonal months
  • Symptoms present ≥2 years
  • Seasonal episodes predominate over nonseasonal episodes
  • Screen for: Prior mania/hypomania, suicidal ideation.

HISTORY

  • MDD Symptoms: Sleep changes, anhedonia, guilt/worthlessness, fatigue, poor concentration, appetite/weight changes, psychomotor retardation, suicidality.
  • Winter SAD: Hypersomnia, hyperphagia (carbohydrate craving), weight gain, daytime fatigue.
  • Spring-Summer SAD: Insomnia, decreased appetite.
  • Collateral history may help define seasonality.

PHYSICAL EXAM

  • Exclude other organic/medical causes.

DIFFERENTIAL DIAGNOSIS

  • Endocrinopathies (hypothyroid), anemia, autoimmune, viral syndromes, substance use disorders.

DIAGNOSTIC TESTS & INTERPRETATION

  • Labs: TSH, CBC, electrolytes, glucose, 25-OH vitamin D, urine tox screen if indicated, pregnancy test (if appropriate).
  • Polysomnography: Shows increased REM sleep (not routine).
  • Imaging: Not routinely needed unless focal findings.

TREATMENT

First Line

  • SSRIs: Sertraline, paroxetine, fluoxetine, citalopram, escitalopram at standard antidepressant doses. May decrease dose in off-season.
  • Bupropion: Only FDA-approved drug for SAD prevention.
  • Light Therapy: As effective as medications; can be used alone or with meds. More efficacious when combined.
  • Melatonin: Low-dose evening administration (with morning light) may help shift circadian rhythm.

Second Line

  • Short-acting β-blockers: Used pre-dawn in resistant cases (suppresses melatonin).

Phototherapy Details

  • Intensity: ≥2,500 lux (domestic lights: 200–500 lux); 7,000–10,000 lux often used.
  • Duration: 30 min–few hours daily.
  • Timing: Best effect with morning exposure.
  • Side Effects: Eye strain, headache, possible insomnia/mania if used late in day.
  • Dawn Simulation: Gradual light increase during sleep may be as effective as standard therapy.

Additional Therapies

  • Stress Reduction: Meditation, lifestyle modifications.
  • Vitamin D: No consistent evidence for benefit (typical doses 400–800 IU/day).

Referral

  • Ophthalmology: Ocular disease before/after phototherapy.
  • Psychiatry: Nonresponse, emergence of mania, suicidal ideation.

Admission

  • Indicated for suicidal ideation or loss of function due to mood episode.

ONGOING CARE

  • Monitor weekly at treatment initiation (SSRIs/light) for response, side effects, suicidality.
  • Symptom Remission: Usually within 3–6 weeks if treated; natural remission by spring.

DIET

  • Cravings: Patients may crave carbohydrates and gain weight in winter.

PATIENT EDUCATION

  • Increase time outdoors in daylight.
  • Arrange home/work space for maximum sunlight.
  • Light therapy boxes: Use only reputable devices; blue-light LEDs may be effective alternatives.
  • Dawn simulation as alternative if standard therapy is less tolerable.

PROGNOSIS

  • Untreated, symptoms remit with spring light, recur each winter.
  • Treated, symptoms improve in 3–6 weeks.
  • Monitor for suicidal ideation and mania.

COMPLICATIONS

  • Suicidal ideation, mania (especially with SSRIs or light therapy).

ICD-10

  • F33.9 Major depressive disorder, recurrent, unspecified
  • F33.0 Major depressive disorder, recurrent, mild
  • F33.1 Major depressive disorder, recurrent, moderate

CLINICAL PEARLS

  • Ask about seasonality in all mood disorder patients.
  • SAD patients: "Sleep too much, eat too much (carbs/sweets), gain weight in winter."
  • Exclude organic/substance causes.
  • SSRIs preferred for acute/severe cases or contraindications to light therapy.
  • SSRIs can increase suicidality in some—monitor every 1–2 weeks early.
  • Light therapy boxes should be from reliable suppliers; dawn simulation is effective for some.