How do you distinguish Major Depressive Disorder from Persistent Depressive Disorder in diagnostic terms?

• A. MDD is episodic with 5+ symptoms in 2 weeks (with impairment); PDD is chronic depressed mood most of the day for at least 2 years (1 year in youth) with fewer symptoms.
• B. MDD is a chronic mood disorder; PDD is episodic with 5+ symptoms.
• C. MDD occurs only in children; PDD only in older adults.
• D. There is no difference between MDD and PDD.

Answer: (B)

The key distinction is pattern and duration of symptoms. Major Depressive Disorder is defined by discrete episodes. An episode involves five or more depressive symptoms over a two-week period, representing a change from prior functioning, and it causes clinically significant impairment. These episodes are episodic—clear starts and stops—with full recovery possible between them.

Persistent Depressive Disorder is defined by a chronically depressed mood that lasts most of the day, for most days, for at least two years in adults (one year in children and adolescents). During that long stretch, there must be two or more additional symptoms, and periods of relatively normal mood are brief (not longer than a couple of months). This makes PDD a long-standing, persistent pattern rather than a series of separate, high-intensity episodes.

So, the main idea clinicians test here is: MDD = episodic, with a threshold of 5+ symptoms for at least 2 weeks; PDD = chronic depressive mood most of the day for most days over 2 years (1 year in youth) with fewer symptoms. It’s also possible for MDD to occur on top of PDD, leading to double depression.