In a 16-year-old adolescent with a two-month history of pervasive sadness, anhedonia, hypersomnia, fatigue, concentration difficulties, declining academic performance, and symptom worsening during menses, which diagnosis is most likely: major depressive disorder, persistent depressive disorder, or premenstrual dysphoric disorder?

Major Depressive Disorder

Based on the clinical presentation of pervasive sadness, anhedonia, hypersomnia, fatigue, and concentration difficulties lasting two months with functional impairment (declining grades), this 16-year-old most likely has major depressive disorder (MDD), not persistent depressive disorder or premenstrual dysphoric disorder. 1

Diagnostic Reasoning

The key diagnostic features that point to MDD include:

• Duration and pattern: Symptoms present "all day for most days" over a two-month period, meeting the DSM criteria for MDD which requires at least two weeks of symptoms 1, 2
• Core depressive symptoms: The patient exhibits both required core symptoms - depressed mood (feeling sad) and anhedonia (lost interest in activities she used to enjoy)
• Additional neurovegetative symptoms: Hypersomnia, fatigue, and concentration difficulties are classic associated symptoms of MDD 3
• Functional impairment: Declining grades and inability to complete missing work demonstrate significant impairment in a key domain (school functioning), which is required for MDD diagnosis 1

Why Not the Other Diagnoses?

Persistent Depressive Disorder (Dysthymia) requires symptoms to be present for at least one year in adolescents, not just two months. This patient's two-month duration is insufficient for this diagnosis.

Premenstrual Dysphoric Disorder (PMDD) is excluded because:

• PMDD symptoms must be limited to the luteal phase of the menstrual cycle and remit within a few days after menses onset 4, 5
• This patient reports feeling sad "all day for most days in the past two months" - a continuous pattern, not cyclical
• While she notes symptom worsening during menses, the baseline symptoms persist throughout the month, which is inconsistent with PMDD 6, 4
• The presence of pervasive symptoms outside the premenstrual period indicates MDD, potentially with premenstrual exacerbation 6

Clinical Pitfalls to Avoid

Do not mistake premenstrual exacerbation of depression for PMDD. Research shows that 46.4% of those with depressive symptoms who also have premenstrual worsening actually have major depression, not PMDD 6. The distinguishing feature is whether symptoms are present throughout the month (MDD) or only during the luteal phase (PMDD).

In adolescents, pay attention to age-specific presentations. While this patient shows classic symptoms, adolescent depression can present with irritability as prominently as sadness, and hypersomnia is particularly common in this age group 3.

Immediate Management Priorities

Per GLAD-PC guidelines, once MDD is identified, you must 1:

1. Conduct a safety assessment immediately - evaluate for suicidal ideation, plan, intent, and access to lethal means, as over 50% of adolescent suicide victims had depression
2. Establish a safety plan including restricting access to lethal means, engaging a concerned third party, and creating an emergency communication mechanism
3. Educate the patient and family about depression as a potentially recurring condition, expected outcomes, and treatment options
4. Set specific treatment goals in key functional domains: home, peer relationships, and school performance

The PHQ-9 score of 16 indicates moderately severe depression, warranting active treatment rather than watchful waiting 2.