How is persistent depressive disorder/dysthymia diagnosed?

It’s diagnosed based on a clinical assessment by a mental health professional.

There’s no lab test for it; instead, the diagnosis relies on interviews, symptom history, duration, and how the symptoms impact daily functioning.

1. Diagnostic criteria (DSM-5)

To be diagnosed with PDD, the DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, 5th Edition) outlines the following:

• • A depressed mood for most of the day, more days than not, for at least:

• • • 2 years in adults.

• • • 1 year in children or adolescents (can appear as irritable mood in kids).

• • Plus at least 2 of these symptoms:

• • • Poor appetite or overeating.

• • • Insomnia or hypersomnia.
      

• • • Low energy or fatigue.

• • • Low self-esteem.

• • • Poor concentration or difficulty making decisions.

• • • Feelings of hopelessness.

• • Symptoms must be persistent, meaning:

• • • The person hasn’t been symptom-free for more than two months at a time during the two years.

• • Not better explained by:

• • • A major depressive episode that lasted the entire 2 years (though double depression, PDD + MDD, is possible).

• • • Other mental disorders (e.g., bipolar, psychotic disorders).

• • • Medical conditions or substance use.

2. Clinical interview
   
   

The clinician will usually use a structured or semi-structured interview, such as:

• • SCID (Structured Clinical Interview for DSM Disorders).

• • MINI (Mini International Neuropsychiatric Interview).

They’ll ask about:

• • Onset of symptoms.

• • Duration and frequency.

• • Mood patterns over time.

• • Functioning in daily life (work, relationships, self-care).

• • Past trauma or stressors.

• • Family history of mood disorders.

3. Rule out other causes

Since PDD shares symptoms with many other conditions, clinicians will rule out:

• • Medical conditions

Thyroid disorders, anemia, and vitamin deficiencies.

• • Substance-induced depression
    
    

Alcohol, sedatives, medications.

• • Other psychiatric disorders

Bipolar disorder, cyclothymia.

Basic lab tests (like a thyroid panel, complete blood count, or B12 levels) might be ordered to rule out underlying health issues.

4. Screening tools (for initial evaluation, not diagnosis)

These tools do not diagnose PDD but help flag possible depression:

• • PHQ-9 (Patient Health Questionnaire-9).

• • Beck Depression Inventory (BDI).

• • Hamilton Depression Rating Scale (HAM-D).

For PDD, the focus is on chronicity rather than severity, which can be tricky.

That’s why clinical interviews are essential.

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