Updates in the medical management of Parkinson disease
ABSTRACTMost, if not all, currently available drugs for Parkinson disease address dopaminergic loss and relieve symptoms. However, their adverse effects can be limiting and they do not address disease progression. Moreover, nonmotor features of Parkinson disease such as depression, dementia, and psychosis are now recognized as important and disabling. A cure remains elusive. However, promising interventions and agents are emerging. As an example, people who exercise regularly are less likely to develop Parkinson disease, and if they develop it, they tend to have slower progression.
KEY POINTS
- Parkinson disease can usually be diagnosed on the basis of clinical features: slow movement, resting tremor, rigidity, and asymmetrical presentation, as well as alleviation of symptoms with dopaminergic therapy.
- Early disease can be treated with levodopa, dopamine agonists, anticholinergics, and monoamine oxidase-B inhibitors.
- Advanced Parkinson disease may require a catechol-O-methyltransferase (COMT) inhibitor, apomorphine, and amantadine (Symmetrel). Side effects include motor fluctuations, dyskinesias, and cognitive problems.
NONMOTOR FEATURES OF PARKINSON DISEASE
Dementia: One of the most limiting nonmotor features
Often the most limiting nonmotor feature of Parkinson disease is dementia, which develops at about four to six times the rate for age-matched controls. At a given time, about 40% of patients with Parkinson disease have dementia, and the risk is 80% over 15 years of the disease.
If dementia is present, many of the drugs effective against Parkinson disease cannot be used because of exacerbating side effects. Treatment is mainly restricted to levodopa.
The only FDA-approved drug to treat dementia in Parkinson disease is the same drug for Alzheimer disease, rivastigmine (Exelon). Its effects are only modest, and its cholinergic side effects may transiently worsen parkinsonian features.22
Psychosis: Also very common
About half of patients with Parkinson disease have an episode of hallucinations or delusions in their lifetime, and about 20% are actively psychotic at any time. Delusions typically have the theme of spousal infidelity. Psychosis is associated with a higher rate of death compared with patients with Parkinson disease who do not develop it. Rebound psychosis may occur on withdrawal of antipsychotic medication.23–27
Patients who develop psychosis should have a physical examination and laboratory evaluation to determine if an infection or electrolyte imbalance is the cause. Medications should be discontinued in the following order: anticholinergic drug, amantadine, MAO-B inhibitor, dopamine agonist, and COMT inhibitor. Levodopa and carbidopa should be reduced to the minimum tolerable yet effective dosages.
For a patient who still has psychosis despite a minimum Parkinson drug regimen, an atypical antipsychotic drug should be used. Although clozapine (Clozaril, FazaClo) is very effective without worsening parkinsonism, it requires weekly monitoring with a complete blood count because of the small (< 1%) risk of agranulocytosis. For that reason, the first-line drug is quetiapine (Seroquel). Most double-blind studies have not found it to be effective, yet it is the drug most often used. No other antipsychotic drugs are safe to treat Parkinson psychosis.
Many patients with Parkinson disease who are hospitalized become agitated and confused soon after they are admitted to the hospital. The best treatment is quetiapine if an oral drug can be prescribed. A benzodiazepine—eg, clonazepam (Klonopin), lorazepam (Ativan), diazepam (Valium)—at a low dose may also be effective. Haloperidol, risperidone, and olanzapine should not be given, as they block dopamine receptors and worsen rigidity.
Mood disturbances
Depression occurs in about half of patients with Parkinson disease and is a significant cause of functional impairment. About 25% of patients have anxiety, and 20% are apathetic.
Depression appears to be secondary to underlying neuroanatomic degeneration rather than a reaction to disability.28 Fortunately, most antidepressants are effective in patients with Parkinson disease.29,30 Bupropion (Wellbutrin) is a dopamine reuptake inhibitor and so increases the availability of dopamine, and it should also have antiparkinsonian effects, but unfortunately it does not. Conversely, selective serotonin reuptake inhibitors (SSRIs) theoretically can worsen or cause parkinsonism, but evidence shows that they are safe to use in patients with Parkinson disease. Some evidence indicates that tricyclic antidepressants may be superior to SSRIs for treating depression in patients with Parkinson disease, so they might be the better choice in patients who can tolerate them.
Compulsive behaviors such as punding (prolonged performance of repetitive, mechanical tasks, such as disassembling and reassembling household objects) may occur from levodopa.
In addition, impulse control disorders involving pathologic gambling, hypersexuality, compulsive shopping, or binge eating occur in about 8% of patients with Parkinson disease taking dopamine agonists. These behaviors are more likely to arise in young, single patients, who are also more likely to have a family history of impulsive control disorder.31
THE FUTURE OF DRUG THERAPY
Clinical trials are now testing new therapies that work the traditional way through dopaminergic mechanisms, as well as those that work in novel ways.
A large international trial is studying patients with newly diagnosed Parkinson disease to try to discover a biomarker. Parkinson disease is unlike many other diseases in that physicians can only use clinical features to measure improvement, which is very crude. Identifying a biomarker will make evaluating and monitoring treatment a more exact science, and will lead to faster development of effective treatments.
