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Parkinson Disease: Phenomenology and Treatment of the Most Common Psychiatric Symptoms

Parkinson Disease: Phenomenology and Treatment of the Most Common Psychiatric Symptoms

Parkinson disease (PD) is a progressive neurodegenerative disorder that is characterized by its motor signs, including resting tremor, rigidity, bradykinesia, and postural instability. PD is more common in the elderly, and there is usually no family history of the disease. The cause of PD is unknown but involves the loss of dopamine in the substantia nigra and striatum, and the presence of Lewy body neuronal inclusions. PD is diagnosed clinically, with definitive diagnosis obtained at autopsy. In atypical clinical presentations, MRI can be helpful in detecting other causes, such as vascular parkinsonism. Functional neuroimaging, such as single photon emission computed tomography and positron emission tomography, is primarily used in research and not in routine clinical work because of its high cost and restricted availability.

Familial PD occurs in young people and is linked to both autosomal dominant and recessive "PARK" genes. Although important for insight into the molecular pathogenesis of PD and therapeutics, genetic testing for mutations is thus far of little clinical use. MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), a by-product of the synthesis of meperidine used in synthetic heroin, is the only environmental agent directly linked to parkinsonism. Cigarette smoking and habitual caffeine intake may lessen the risk of parkinsonism, but the mechanism of this effect is not known. Treatment of PD is aimed at reducing motor symptoms with dopamine replacement therapy.

Although PD is primarily a movement disorder, psychiatric disturbances are prevalent and include depression, anxiety, psychosis, and dementia. The psychiatrist has an important role in treating PD patients because the behavioral aspects of PD are frequently more disabling than the motor symptoms and often complicate the course of the disease. This review will focus on the phenomenology and treatment of the most common psychiatric disturbances in PD.

Depression

Depression is one of the most common psychiatric conditions in PD, occurring in 40% to 50% of patients.1 Minor depression and dysthymia account for a large proportion of symptoms.1 Despite its high prevalence, PD depression is frequently undiagnosed.2 This may be due in part to the difficulty of recognizing depression in PD because depressive symptoms often mimic those of PD (such as flat affect, psychomotor retardation, fatigue, weight loss, sleep disturbance, and decreased libido). PD depression may also present differently from primary major depression, with less sadness, anhedonia, and guilt but with greater anxiety, pessimism, and decreased concentration.1,3,4 Depression may occur at any stage of PD and can precede the development of motor symptoms.1

The cause of depression in PD is unknown but may involve neuronal loss and a reduction in serotonin, norepinephrine, and dopamine.5 PD depression may also represent a reaction to having an incurable and debilitating disease. In a study comparing PD patients with patients who have rheumatoid arthritis, depression was found to occur with equal frequency in both groups and was related to the severity of illness and functional disability.3

It is important to identify depression early in PD because it leads to more rapid cognitive decline,6 greater motor disease severity,3 and disability.3,6 In our study, we found that the severity of depression was a significant risk factor for sleep disturbance in PD patients.7 It is recommended that PD patients be screened regularly for depression. The Geriatric Depression Scale and Hamilton Rating Scale for Depression are validated in the PD population8 and can be used to monitor treatment response.

Controlled studies examining the efficacy of antidepressants in PD depression are lacking. A meta-analysis found no difference between active treatment and placebo in PD depression.9 The American Academy of Neurology (AAN) Practice Parameter on the treatment of depression, psychosis, and dementia in PD has recommended that amitriptyline be considered in the treatment of PD depression but because of its adverse-effect profile, this may not necessarily be the first-choice antidepressant.10 The AAN report concluded that there was insufficient evidence to make other recommendations.10

Open-label trials with SSRIs in PD suggest a beneficial effect on depression. However, to date, the efficacy of SSRIs in the treatment of PD depression has not been demonstrated since the 2 placebo-controlled trials yielded negative findings.11,12 In the studies, despite treatment effects in both the citalopram and sertraline groups, there were no statistically significant differences in response rate between treatment and placebo.11,12 However, the studies were limited by insufficient power. Most PD patients tolerate SSRIs without worsening of PD,but caution should be observed when using SSRIs or tricyclic antidepressants (TCAs) in combination with selegiline or rasagiline because of the risk of serotonin syndrome.

As is the case for the general population, the SSRIs are recommended as first-choice antidepressants for PD patients because they are well tolerated, with few adverse effects and drug-drug interactions. Other possible first-line antidepressants include venla-faxine, duloxetine, mirtazapine, and bupropion; however, clinical trials demonstrating their efficacy in PD depression are lacking. In addition to treating depression, mirtazapine can improve tremor and levodopa (l-dopa)-induced dyskinesias in patients with PD.13 Because of its dopaminergic activity, bupropion may precipitate psychosis in PD patients. Since most PD patients are elderly, they may be susceptible to the adverse effects of TCAs, such as orthostatic hypotension, worsened cognition, and cardiovascular effects. Thus, TCAs are recommended as second-line antidepres- sants. However, low doses of TCAs may be beneficial in some patients with PD to reduce drooling, inhibit an overactive bladder, and treat insomnia.

Antiparkinsonian medications, including selegiline, bromocriptine, pergolide, and pramipexole, are reported to have antidepressant effects.14-16 Electroconvulsive therapy is beneficial in patients with medication-refractory depression and usually improves motor function.17 Psychotherapy may be helpful in patients with PD who have mild depression and can be used to augment treatment response to pharmacotherapy.

Anxiety

Anxiety disorders occur in up to 40% of PD patients,18 compared with 5% to 15% of the general population.19 The most common anxiety disorders in PD are panic disorder, generalized anxiety disorder, and social phobia.18,19 Although anxiety is reported to occur after diagnosis of PD,18 a case-control study found that anxiety disorders were significantly associated with subsequent PD and were present for up to 20 years before onset of motor symptoms.20 Anxiety is reported to occur in patients who experience motor fluctuations, especially during the "off" phase, when antiparkinsonian medication wears off.21,22 Alterations in serotonin and norepinephrine are believed to play important roles underlying anxiety.21 There is no consensus on whether medications used to treat motor symptoms in PD are responsible for anxiety symptoms. While an increase in panic attacks in patients on l-dopa therapy has been reported,21 other studies found no association between antiparkinsonian medication and anxiety.22,23 One controlled study found that l-dopa produced a dose-related reduction in anxiety and elevation of mood.23

There are no randomized controlled trials of anti-anxiety medication in PD. When evaluating the anxious patient who has PD, it is impor- tant to assess the timing of anxiety, particularly whether it is related to the "off" period, in which case, treatment involves adjustment of antiparkinsonian medications. The SSRIs are first-choice medications, and high doses may be necessary to treat anxiety symptoms. Low doses of short-acting benzodiazepines may be needed initially while the optimal response of the SSRI is attained. However, benzodiazepines should be used with caution because most patients with PD are elderly and susceptible to falls, and there is a risk of dependence. The serotonin-norepinephrine reuptake inhibitors (SNRIs), such as venlafaxine, may be effective in treating anxiety, but there are no data on their efficacy in the PD population. Buspirone has been used in PD, but its efficacy is not apparent.24 Cognitive-behavioral therapy may have a role in treating anxiety in PD patients.

Psychosis

Psychosis is not considered to be a primary symptom of idiopathic PD but occurs in medication-treated patients with PD. Psychosis can also occur as part of a delirium or in patients with dementia. Patients who have PD with psychosis have an increased rate of nursing home placement and an increased mortality rate.25 Up to 40% of patients with PD are reported to have psychotic symptoms—most commonly, visual hallucinations.25 Hallucinations differ from those in primary psychotic disorders in that the images usually lack emotional content and most patients retain insight into the unreality of the image. Hallucinations are typically of people but also include animals, and they generally occur in low-stimulus environments. Most patients are not bothered by the hallucinations, and treatment is not usually required.

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