Rapid cycling patients: conceptual and etiological factors

The concept of rapid cycling is confusing in terms of its definition, clinical features, course of illness and the outcome. To complicate the matter further, rapid cycling has been reported to be drug resistant. Currently this condition has been reported to be secondary to lithium, tricyclic antidepressants and other agents such as cyproheptadine, a serotonin antagonist, piribedil, propranolol and levodopa. The increase in rapid cycling has coincided with the rapid increase in cocaine use in the society even though such an association cannot prove a causal relationship. Clinical or subclinical hypothyroidism as well as hyperthyroidism have been implicated in rapid cycling. In addition to the lack of specific knowledge on the etiology, a number of heterogeneous disorders has been grouped under this entity. It is useful to attempt a classification to ascertain whether clinically distinguishable subgroups have a common or different pathophysiology and to tailor the treatment that is most desirable for each subgroup.