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Evidence-Based Reviews

SAD: Is seasonal affective disorder a bipolar variant?

Patients with seasonal bipolarity require different treatment from those with unipolar SAD

Vol. 9, No. 2 / February 2010

Discuss this article

Ms. S, age 24, is referred to our team in early December by her primary care physician for “fatigue.” The patient describes going to bed and falling asleep before 9:30 these winter evenings, whereas in summer she went to bed at 11 PM. She craves bread, pasta, and sweets and reports increased appetite in winter compared with summer. Her mood is low, and she misses warm-weather activities of gardening and walking. Fatigue and difficulty concentrating are causing her problems at work and school.

Her history reveals mood elevation in spring as days become longer, with a clear change at approximately March 10 to 20. She reports “spring fever” and feeling “great” last year as soon as daylight saving time began. She slept only 3 hours a night and had a burst of ideas to expand her small business. She threw herself into her work, feeling she was making up for lost time and productivity. She also admits to making a large, misguided business investment during that time.

Upon questioning, she recalls that the previous spring she argued with her father and threw a cup of hot tea at him. When interviewed, Ms. S’s mother describes her daughter at that time as having “a very short fuse,” speaking loud and fast, staying up late at night, and looking as though she was not herself.

Seasonal affective disorder (SAD) is an umbrella term for mood disorders that follow a seasonal pattern of recurrence. Bipolar I disorder (BD I) or bipolar II disorder (BD II) with seasonal pattern (BD SP) is the DSM-IV-TR diagnosis for persons with depressive episodes in the fall or winter and mania (BD I) or hypomania (BD II) in spring or summer ( Table 1 ). 1

This article compares BD SP with major depressive disorder with seasonal pattern (MDD SP), in which depressive episodes usually occur in fall or winter and fully remit in spring or summer. 1 Rather than being categorically distinct from each other, BD SP and MDD SP may represent extreme variants on a seasonal depression continuum from unipolar to bipolar.

Table 1

DSM-IV-TR criteria for seasonal pattern specifier*


A regular pattern of major depressive episodes (MDEs) at a particular time of year (such as fall and/or winter)


Full remission or change to mania or hypomania at a particular time of year (such as spring or summer)


2 seasonal MDEs that followed the pattern described in (A) and (B) occurred in the past 2 years (and no nonseasonal MDEs)


Seasonal MDEs substantially outnumber nonseasonal MDEs across the lifespan

Cases do not meet criteria if:

  • seasonal episodes have not been present in the past 2 consecutive winters because individuals have been successfully treated or have lived or traveled in southern locations, despite the expectation that continuing treatment is needed and/or a return to northern locales would precipitate another seasonal episode
  • an obvious psychosocial stressor related to the mood change recurs on a seasonal basis (such as regular winter unemployment, holiday depression, anniversary reactions)

*Can be applied to a pattern of major depressive episodes in bipolar I disorder, bipolar II disorder, or major depressive disorder

Source: Adapted from reference 1

Overlap of MDD SP and BD SP

The seasonal pattern specifier can be applied to a diagnosis of MDD, BD I, or BD II. 1 Seasonality-focused assessments, described below, can help characterize seasonal patterns that do not meet full SP criteria but may deserve clinical attention.

Symptom presentation. MDD SP and BD SP share similar atypical depressive symptom presentations and seasonal recurrence patterns ( Box 1 ). Hypersomnia, hyperphagia, and psychomotor retardation are more prevalent in major depressive episodes of bipolar disorders and SAD than in unipolar or nonseasonal mood disorders. 2-4 Individuals with SAD also report fatigue and decreased physical activity, 3 both of which are characteristic of bipolar depressive episodes. 5

Although psychosis and psychiatric hospitalizations are more common in BD I than unipolar disorders, 6 individuals with BD SP are less likely to report psychosis than those with nonseasonal BD. 7 Another study found that BD SP patients reported a higher rate of psychiatric hospitalizations than MDD SP patients (28% vs 9.4%). 6

Recurrence pattern. Major depressive episodes are highly recurrent in both MDD and BD, with or without a seasonal pattern. Approximately 75% of individuals with MDD experience ≥1 recurrence (mean, 10.8 episodes); 8 MDD SP patients report a mean of 13.4 episodes. 9 The mean lifetime episodes in BD SP is 20.74, compared with 11.67 in nonseasonal BD. 7

Cassidy and Carroll 10 measured the frequency of mood episodes in 304 BD patients not assessed for seasonality. Manic episodes peaked in early spring, mixed episodes peaked in late summer or fall, and depressive episodes peaked in fall-winter.

Irregular rhythm. Both BD and MDD SP involve irregularities in daily or circadian rhythms, such as changes in the timing of sleep, melatonin release, and body temperature. 3,5,11 Circadian phase delays—in which internal rhythms lag behind the sleep cycle—are correlated with symptom severity in BD 12 and are implicated in the core pathology of BD 13 ( Box 2 ). In BD, life events that change social rhythms may disrupt circadian rhythms, triggering mood episodes. 5

Etiologic hypotheses for both BD and SAD propose that an external event (life stress in BD; decreased photoperiod in SAD) leads to circadian dysregulation and, in turn, mood episodes. Circadian-related hypotheses for SAD and BD are supported by evidence showing efficacy of treatments that manipulate behavioral and circadian rhythms.

Box 1

Seasonal affective disorder: A depression continuum
from unipolar to bipolar?

Seasonality refers to the degree of seasonal changes in behavior and mood within an individual. Seasonality scores are normally distributed,a suggesting that seasonality may be continuous in the general population—with some individuals meeting criteria for a seasonal mood disorder:

  • A seasonal pattern is reported by approximately 10% to 20% of depressed outpatients with recurrent mood disorders and an estimated 15% to 22% of individuals with bipolar disorder (BD).b
  • Persons with BD—seasonal or not—report greater seasonality compared with those with major depressive disorder (MDD).c

Among individuals with seasonal affective disorder, the course is bipolar in an estimated 12% to 22% and unipolar in 78% to 88%.d These estimates may reflect underdiagnosis of BD with seasonal pattern because hypomania is difficult to diagnose retrospectively.e

The bipolar-unipolar continuum includes (in order): BD I, BD II, bipolar disorder not otherwise specified, cyclothymia, bipolar spectrum disorder, and MDD.f In examining the validity of the bipolar spectrum model, Phelps et alg noted:

  • At least 3 studies found that all symptoms reported by individuals with unipolar and bipolar diagnoses approach a normal distribution, rather than a bimodal distribution separating unipolar from bipolar symptom profiles.
  • Data from 2 population-based studies indicate that subthreshold hypomanic symptoms are more common than and cause as much impairment as symptoms meeting criteria for BD II or I.

Some individuals who meet criteria for MDD with seasonal pattern have summertime periods of transient hypomania and hyperthymia (hypomanic-like periods without clinically significant impairment).h This suggests that the bipolar continuum also may exist among individuals with seasonal pattern mood disorders.

Source: Access reference citations here

Box 2

Proposed mechanisms for seasonal affective disorder

Etiologic hypotheses of seasonal affective disorder (SAD) include:

  • photoperiodic hypothesis (shorter winter days cause SAD,a perhaps mediated by a summer vs winter difference in duration of nightly melatonin release)b
  • phase shift hypothesis (less available light in winter may lead to an inability to synchronize circadian rhythms with sleep/wake rhythms).c

Some case studies of rapid-cycling bipolar disorder (BD) suggest that mood is correlated with daily hours of sunshine and light therapy is antidepressant. Rapid-cycling patients may be hypersensitive to day-to-day changes in photoperiod, analogous to mood changes in response to changes in photoperiod across the seasons in SAD.d

Circadian phase delays—in which internal rhythms lag behind the sleep cycle—are correlated with symptom severity in BDe and are implicated in the core pathology of BD.f Phase delays also are present in some individuals with SAD and are associated with severity and treatment response.g Preliminary evidence suggests that variation in circadian clock genes is related to both BDf,h and SAD.i

Source: Access reference citations here

CASE CONTINUED: Seasonal pattern revealed

Ms. S was aware that she is vulnerable to depressive episodes in fall and winter but unaware of a pattern of hypomanic/manic episodes in spring and summer. Her family psychiatric history includes a sister diagnosed with BD I (with no seasonal specifier), and a maternal aunt who has attempted suicide several times.

Ms. S agrees to an assessment plan including a diagnostic interview, interviews measuring symptom severity and pattern of recurrence, routine laboratory examination, and self-report questionnaires. These show that she meets DSM-IV-TR criteria for BD I, depressed, moderate, with seasonal pattern.

Her assessment scores are 28 on the Structured Interview Guide for HDRS-seasonal affective disorder version (SIGH-SAD), 17 on the Hamilton Depression Rating Scale (HDRS), and 11 on the atypical subscale. The HDRS and atypical subscale are components of the SIGH-SAD reflecting typical (eg, insomnia, loss of appetite, etc.) and atypical (eg, hypersomnia, increased appetite, etc.) depression symptoms, respectively. Ms. S’s scores exceed the threshold scores defining a BD SP episode (>20 SIGH-SAD + >10 HDRS + >5 atypical subscale 14 ). Data from self-report questionnaires corroborate this assessment.

We plan to administer the Hypomania Interview Guide (including Hyperthymia) for Seasonal Affective Disorder (HIGH-SAD) during treatment and the following spring to monitor prospectively for hypomanic symptoms.

Assessment tools

After complete assessment for mood episodes and mood disorders based on DSM-IV-TR, an additional assessment for bipolarity and seasonality may be helpful. 1

Screen for bipolarity in patients with SAD to avoid triggering mania or hypomania during treatment. Useful tools include:

  • HIGH-SAD 15
  • the National Institutes of Health Life Chart Method to establish a recurrent pattern of mood episodes and track treatment efficacy 16
  • assessments that characterize sub-threshold bipolar symptoms, such as the Bipolar Spectrum Diagnostic Scale 17 ( see Box 3 ) and the Bipolarity Index. 18

Also obtain collateral reports from significant others, review patient records, and use the same mania and hypomania scales for prospective assessment as the next spring approaches. 6

Assess seasonality in patients with BD to improve diagnosis and treatment. Characterizing a seasonal pattern may allow you and your patient to predict episodes and treat proactively. Commonly used assessments include the SIGH-SAD and the Structured Clinical Interview for DSM Disorders (SCID) seasonal pattern specifier module. 19

The SIGH-SAD measures symptom severity and provides recovery criteria based on changes in scores during treatment. Response is defined as a 50% reduction in symptoms; remission is >50% improvement in SIGH-SAD + HDRS <7 + atypical <7 or HDRS <2 + atypical <10. 14

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