What is the most likely diagnosis for a patient presenting with recurrent episodes of decreased interest and pleasure in activities, poor sleep, fatigue, weight gain, and a sense of worthlessness, without symptoms of mania or hypomania?

Major Depressive Disorder

The most likely diagnosis is Major Depressive Disorder (MDD), as this patient presents with recurrent episodes of depressive symptoms lasting several months each, meeting full diagnostic criteria without any seasonal pattern or chronic persistence that would suggest alternative diagnoses. 1

Diagnostic Reasoning

This patient clearly meets the American Psychiatric Association criteria for MDD, which requires at least 5 symptoms during a 2-week period (with at least one being depressed mood or loss of interest/pleasure), causing significant functional impairment 2, 1. She presents with:

• Decreased interest and pleasure in activities (anhedonia)
• Poor sleep (insomnia)
• Fatigue/loss of energy
• Weight gain (appetite disturbance)
• Sense of worthlessness
• Functional impairment ("debilitating symptoms")

This constitutes 5-6 of the required symptoms, easily meeting diagnostic threshold 2, 1.

Why Not the Other Diagnoses?

Seasonal Affective Disorder is ruled out because her episodes lack a consistent seasonal pattern. She describes "four similar episodes over the past few years...without any clear pattern with respect to a calendar year." 1 While one episode occurred in winter following job loss, the absence of a regular seasonal recurrence pattern excludes this diagnosis.

Persistent Depressive Disorder (Dysthymia) is excluded because it requires chronic depressive symptoms persisting for at least 2 years continuously 3. This patient experiences discrete episodes lasting "up to a few months at a time" with complete resolution between episodes ("felt completely normal within a few months"), not the chronic, unremitting course characteristic of dysthymia 3.

Cyclothymia is ruled out because she has never experienced symptoms of mania or hypomania 2. Cyclothymia requires numerous periods of hypomanic symptoms alternating with depressive symptoms over at least 2 years.

Functional Neurologic Symptom Disorder is inappropriate as her symptoms are classic neurovegetative and mood symptoms of depression (sleep disturbance, fatigue, appetite changes, anhedonia, worthlessness) 3, not unexplained neurological symptoms like paralysis, seizures, or sensory deficits.

Clinical Pattern Recognition

The recurrent episodic nature with full inter-episode recovery is entirely consistent with recurrent MDD 4, 5. MDD commonly presents with multiple discrete episodes throughout a person's lifetime, each lasting weeks to months if untreated 5. The fact that one episode was triggered by job loss (a psychosocial stressor) does not change the diagnosis to adjustment disorder, as the symptom severity, duration (several months), and functional impairment exceed what would be expected in adjustment disorder 3.

Critical Next Steps

Immediate suicide risk assessment is mandatory, as suicidal ideation is part of the diagnostic criteria and has critical safety implications 2, 3. This should be completed before finalizing any treatment plan 2.

Treatment should include either cognitive behavioral therapy (CBT) or second-generation antidepressants (SSRIs/SNRIs) as first-line options, with both having equivalent effectiveness based on moderate-quality evidence 1. Given the recurrent nature (four episodes), continuation treatment for at least 4-9 months after response is essential, with consideration of maintenance therapy ≥1 year given the recurrent pattern 1.