Nonmotor disorders and their correlation with dopamine: can they be treated by currently available methods?

Many of the nonmotor symptoms in Parkinson disease have a dopaminergic basis, whether the result of dopaminergic degeneration or as a result of dopaminergic treatment. In the latter case, the symptoms may be genuine side effects of drugs (hypotension, pathologic gambling, etc.) or they may be secondary either to the pathoplastic effect they have on the natural course of the disease (nonmotor fluctuations) or to the lack of dopamine (apathy, depression, dopamine withdrawal syndrome, etc.). In all these cases, dopaminergic treatment can be helpful. However, many other nonmotor (and motor) symptoms will have no correlation with dopamine; therefore, they require different treatments, very often with little efficacy, as in apathy or cognitive decline.