Findings regarding the association are equivocal.
Plausible explanations include study design, case definition, and confounding disease states. Most of the evidence supporting an association has used case series and case reports. Case definition and measurement instruments may partially explain these inconsistencies. Studies using a diagnosis of depression generally do not support the relationship. Trials using depressive symptoms are about evenly split, but they have generally enrolled a small number of patients and have questionable statistical power.