Everything I've read so far shows it as being a mood disorder, a chronic form of depression. Yes, I would say it affects your personality, just like any form of depression does, but I wouldn't say that would make it a personality disorder.

Dysthymic Disorder
SYMPTOMS

Dysthymic Disorder (also known more generally as "dysthymia") is characterized by an overwhelming yet chronic state of depression, exhibited by a depressed mood for most of the days, for more days than not, for at least 2 years. (In children and adolescents, the mood can be irritable and duration must be at least 1 year.) The person who suffers from this disorder must not have gone for more than 2 months without experiencing two or more of the following symptoms:

* Poor appetite or overeating
* Insomnia or hypersomnia
* Low energy or fatigue
* Low self-esteem
* Poor concentration or difficulty making decisions
* Feelings of hopelessness

Furthermore, in order to be diagnosed with Dysthymic Disorder, no Major Depressive Episode has been present during the first two years (or one year in children and adolescents) and there has never been a Manic Episode, a Mixed Episode, or a Hypomanic Episode, and criteria have never been met for Cyclothymic Disorder. This generally means that the person needs to have had an uncomplicated, long-term, low-grade depression for two or more years in order to meet this diagnosis.

In order to meet the diagnostic criteria for Dysthymic Disorder, the symptoms may not be due to the direct physiological effects of a the use or abuse of a substance (for instance, alcohol, drugs, or medications) or a general medical condition (e.g., cancer or a stroke). The symptoms must also cause significant distress or impairment in social, occupational, educational or other important areas of functioning.

General Treatment for Dysthymic Disorder


Criteria summarized from:
American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders, fourth edition. Washington, DC: American Psychiatric Association.