RESUMEN
Patients with hyperthymic and cyclothymic temperaments often develop symptoms that fail to meet diagnostic criteria for bipolar disorders. These patients can be conceived as having bipolar disorder NOS (not otherwise specified), a bipolar spectrum disorder, cyclothymic disorder or cluster B personality traits. Here, we describe four of these patients with mild to moderate symptoms affecting mood, behaviour, emotional reactivity and sleep. Treatment with low-dose quetiapine (25-75 mg/day at night) lead to sustained symptom remission. Two of them were on quetiapine monotherapy. Such low doses occupy a minority of D2 and 5-HT2 receptors, which may nevertheless be of therapeutic value in mild cases. Alternatively, other mechanisms more likely to occur at low doses, such as antagonism of H1, alpha(1B)-adrenergic and other serotonin receptors, as well as reduction cortisol secretion, may be involved in the therapeutic efficacy of quetiapine.