Mislabeling Chronic Depression: A Case Report of Persistent Depressive Disorder Misdiagnosed for 12 Years

Persistent depressive disorder (PDD) is a chronic mood condition defined by a depressed mood lasting at least two years. However, it is frequently misdiagnosed as episodic depression, such as major depressive disorder (MDD) or recurrent depressive disorder (RDD), or attributed to personality-based pathology such as emotionally unstable personality disorder (EUPD). We present the case of a 48-year-old woman with a lifelong low mood and passive death wishes, who, for 12 years, received multiple shifting diagnoses and underwent extensive antidepressant and augmentation trials, as well as a full course of dialectical behaviour therapy (DBT), without achieving meaningful improvement. Longitudinal assessment demonstrated a continuous depressive baseline with intermittent past worsening, but no sustained remission exceeding two months, preserved occupational functioning, and absence of behavioural dysregulation, supporting a diagnosis of PDD with intermittent major depressive episodes, without current episode (Type 3). Misdiagnosis resulted from functional masking of severity, a clinical bias toward episodic interpretation of mood fluctuation, and misattribution of emotional sensitivity as personality pathology. Accurate recognition of PDD is clinically essential, as it reframes treatment goals toward long-term management rather than pursuit of full remission, stabilizes the therapeutic alliance, and prevents treatment fatigue and disengagement.