Cyclothymic disorder (CD), also termed cyclothymia, is a mental disorder with mild but long-lasting and severely impairing mood swings. Characteristic mood changes include periods of euphoria which are abruptly followed by depressive episodes.
CD is part of the spectrum of bipolar disorders and can progress to bipolar disorder type 1 or 2. Onset usually occurs in adolescence and affects both genders equally. Prevalence is estimated to be up to 1/100. Progression to bipolar disorder occurs in up to 50% of cases.
CD may only be diagnosed if the specific mood swings persist for two years in adults or one year in adolescents.
Expert consensus defines cyclothymic disorder (CD) as a subclinical variant of bipolar disorder, which is characterized by chronic mood swings alternating between hypomanic and depressive periods. Due to the subclinical nature of CD, it has also been incorrectly assessed as a character trait in the past   .
A cardinal feature of all types of bipolar disorders is perturbed sleeping, which also applies to CD  . Long-term studies have shown that CD is as debilitating as other disorders of the bipolar spectrum  .
Hypomanic episodes may manifest with general euphoria, exaggerated self-esteem, logorrhea, impaired risk assessment, distractability, lack of concentration, racing thoughts, no need for sleep and marked irritability  .
CD patients have described their depressive periods with a feeling of fatigue, demoralization, persistent irritability, restlessness, guilt, low self-esteem and sleep disturbances together with weight changes and even suicidal thoughts  .
CD shows significant clinical overlap with major depressive episodes and bipolar disorders type 1 and 2 and can progress to the latter . The exact etiology of CD remains unknown.
Diagnosing cyclothymic disorder requires a physical examination to check for potential causes of mood swings, a psychological evaluation to analyze the patient's mood swings with questionnaires and professional interviews. The patient's family and close friends may be included in this psychological analysis to obtain a complete picture of the mood swings and their frequency. Moreover, cases should keep track of their mood swings with a mood chart and record their sleeping hours.
Clinical criteria for CD are persistent episodes of hypomania and depression for at least one year in adolescents and two years in adults with intermittently stable mood periods shorter than two months. Characteristic findings cannot be traced back to other causes like substance abuse, and significantly affect the patient's social interactions .
Hypomanic CD symptoms in children are hard to distinguish from characteristic attention deficit hyperactivity disorder (ADHD) signs making CD a non-trivial diagnosis. Manic episodes never occur in CD  .
Progression of CD to bipolar disorder type 1 and 2 can be prevented with professional treatment. A late onset of CD hints towards substance abuse.