Non-Motor Symptom Treatment in Parkinson's Disease

Non-motor symptoms (NMS) are among the most disabling features of Parkinson's disease, often surpassing motor impairment as the primary driver of reduced quality of life, caregiver burden, and institutionalization. Depression, cognitive decline, psychosis, autonomic dysfunction, and sleep disturbances affect virtually all PD patients over the disease course, yet they remain systematically undertreated — a recent Swedish registry study found that only 4% of patients with excessive daytime sleepiness and 0% with dysphagia received guideline-concordant treatment. This article reviews the evidence-based management of non-motor symptoms, anchored in the MDS Evidence-Based Medicine Reviews (Seppi et al., 2011; Seppi et al., 2019) and landmark clinical trials.

PD Psychosis

Psychosis in PD encompasses a spectrum from minor phenomena (passage hallucinations, presence hallucinations, illusions) to formed visual hallucinations and frank paranoid delusions. Prevalence increases with disease duration, reaching 20–40% in established PD. Psychosis is one of the strongest predictors of nursing home placement and is independently associated with increased mortality.

The first management step is always identifying and treating precipitants: infection, dehydration, metabolic derangement, and medication review. Anticholinergics, amantadine, and dopamine agonists are the most common pharmacologic triggers and should be reduced or discontinued before adding an antipsychotic. The general principle of medication reduction follows a stepwise approach: anticholinergics → amantadine → dopamine agonists → COMT inhibitors → MAO-B inhibitors → levodopa dose reduction (last resort).

Pimavanserin — The HARMONY Trial

Pimavanserin (Nuplazid) is a selective serotonin 5-HT_2A inverse agonist with no dopaminergic, histaminergic, adrenergic, or muscarinic activity — making it the only antipsychotic that does not worsen parkinsonism. It was FDA-approved in 2016 for PD psychosis based on the pivotal ACP-103-020 trial, and later studied in the broader HARMONY trial⁽¹⁾.

HARMONY was a Phase 3 randomized discontinuation trial of pimavanserin in dementia-related psychosis (including PD dementia, Alzheimer's, DLB, FTD, and vascular dementia). Of 392 patients who received open-label pimavanserin for 12 weeks, 217 responders (61.8%) were randomized to continue pimavanserin 34 mg/day or switch to placebo. Psychosis relapse occurred in 13% of pimavanserin-treated patients versus 28% on placebo (HR 0.35; 95% CI 0.17–0.73; P=0.005; NNT ≈ 7). The trial was stopped early for efficacy. Criticisms include the enriched-responder design, early termination potentially overestimating effect size, and limited racial diversity⁽¹⁾.

Clozapine

Clozapine is the only antipsychotic designated "clinically useful" by the MDS EBM Review for PD psychosis. Low-dose clozapine (6.25–50 mg/day, typically 12.5–25 mg at bedtime) effectively reduces hallucinations and delusions without worsening parkinsonism. Its use is limited by the mandatory REMS program requiring regular complete blood counts due to the risk of agranulocytosis (~1–2%). Other monitoring concerns include metabolic syndrome, sedation, sialorrhea (paradoxically), and rare myocarditis⁽²⁾.

Quetiapine

Quetiapine is the most widely prescribed antipsychotic for PD psychosis in clinical practice, despite receiving only an "insufficient evidence" designation from the MDS EBM Review. Two small RCTs were negative, but extensive open-label and clinical experience supports its use at low doses (12.5–150 mg/day). Quetiapine is generally well tolerated, with sedation and orthostatic hypotension as the primary concerns. Most movement disorder specialists use quetiapine as a pragmatic first-line agent, reserving clozapine for refractory cases⁽²⁾.

PD Dementia & Cognitive Impairment

Cognitive impairment is one of the most consequential non-motor features of PD. Mild cognitive impairment (PD-MCI) affects 20–30% of patients at any given time, with executive dysfunction and visuospatial deficits as the earliest and most characteristic domains affected. PD dementia (PDD) develops in approximately 30% at a given point in time, with cumulative incidence reaching ~80% over the disease course. Risk factors for PDD include older age, longer disease duration, PIGD motor subtype, lower education, and GBA1 mutations.

Rivastigmine — The EXPRESS Trial

EXPRESS (Emre et al., 2004) was the landmark trial establishing cholinesterase inhibitor therapy for PDD. A total of 541 patients with PDD (diagnosed by DSM-IV criteria, with PD onset ≥2 years before dementia) were randomized 2:1 to rivastigmine (3–12 mg/day) or placebo for 24 weeks⁽³⁾.

Rivastigmine significantly improved the primary cognitive outcome (ADAS-cog: +2.1 vs −0.7 points, P<0.001) and the co-primary global measure (ADCS-CGIC: 3.8 vs 4.3, P=0.007). Secondary outcomes including activities of daily living, neuropsychiatric symptoms (NPI-10, P=0.02), and MMSE (P=0.03) also improved. However, GI side effects were substantially more common with rivastigmine: nausea (29% vs 11%), vomiting (17% vs 2%), and tremor worsening (10% vs 4%). The dropout rate was higher in the rivastigmine group (27% vs 18%)⁽³⁾.

Based on EXPRESS, rivastigmine (oral and transdermal patch) is the only FDA-approved treatment for PDD. The transdermal patch (Exelon Patch) offers improved GI tolerability and is preferred by many clinicians. The MDS EBM Review rates rivastigmine as "clinically useful" for PDD⁽²⁾.

Depression & Anxiety

Depression affects 35–50% of PD patients and is often underdiagnosed due to symptom overlap with PD itself (psychomotor slowing, masked facies, fatigue, sleep disturbance). It may precede motor onset by >5 years and is among the strongest predictors of impaired quality of life. Anxiety (generalized, panic, social) co-occurs in 25–40% and often fluctuates with motor state in patients with wearing off.

The MDS EBM Review (Seppi et al., 2011; updated 2019) provides the following efficacy designations for PD depression⁽²⁾:

Pramipexole is designated "clinically useful" for PD depression, based on a large RCT (Barone et al., 2010) showing significant improvement in depression scores independent of motor improvement. This makes it a particularly efficient choice in patients with both motor symptoms and depression. Venlafaxine and desipramine are rated "likely efficacious" based on the SAD-PD trial (Richard et al., 2012), which found both superior to placebo. SSRIs (paroxetine, citalopram, sertraline) have mixed trial data but are widely used in clinical practice; the MDS rates them as "insufficient evidence" for PD-specific depression, though they are generally considered first-line in practice. Nortriptyline showed benefit in a small RCT (Menza et al., 2009) and is rated "likely efficacious" — its anticholinergic properties may help with sialorrhea but limit use in older patients and those with cognitive impairment⁽²⁾.

Cognitive behavioral therapy (CBT) has Level I evidence for PD depression (Dobkin et al., 2011) and is recommended as monotherapy or adjunct. Exercise — particularly structured aerobic programs — has growing evidence for both depression and anxiety in PD.

For anxiety, there are very few PD-specific RCTs. SSRIs and SNRIs are used empirically based on general anxiety disorder data. Benzodiazepines should be minimized due to fall risk and cognitive impairment. CBT has emerging evidence.

Autonomic Dysfunction

Orthostatic Hypotension

Neurogenic orthostatic hypotension (nOH) — defined as a sustained drop of ≥20 mmHg systolic or ≥10 mmHg diastolic within 3 minutes of standing — affects 30–50% of PD patients and is a major cause of falls, syncope, and functional limitation. All dopaminergic medications can worsen OH, and management always begins with non-pharmacologic strategies: adequate fluid intake (2–2.5 L/day), salt supplementation (if no heart failure), compression stockings, abdominal binders, slow postural changes, elevating the head of bed 10–15°, and avoiding large meals.

Pharmacologic options include: Midodrine (α1-agonist; 2.5–10 mg TID; avoid within 4 hours of bedtime due to supine hypertension) — designated "clinically useful" by MDS. Droxidopa (Northera; norepinephrine prodrug; 100–600 mg TID) — FDA-approved for nOH (including PD-related), though the approval was controversial based on modest effect size and short trial durations. Fludrocortisone (0.1–0.3 mg/day; volume expansion) — widely used but "insufficient evidence" per MDS; risk of supine hypertension and heart failure. Supine hypertension is the main safety concern across all agents and should be monitored at every visit⁽²⁾.

Constipation

Constipation is the most common autonomic symptom, affecting 50–80% of PD patients and often preceding motor diagnosis by over a decade. It results from both central (enteric nervous system α-synuclein pathology) and peripheral (medication effects, reduced physical activity) mechanisms. Macrogol (PEG/polyethylene glycol) is the best-studied intervention and is rated "clinically useful" by the MDS. Lubiprostone is "possibly useful." Fiber supplementation, adequate hydration, and exercise form the non-pharmacologic foundation. Probiotics (particularly multi-strain formulations) have emerging evidence but insufficient data for formal recommendation⁽²⁾.

Sialorrhea (Drooling)

Sialorrhea in PD results from impaired swallowing frequency rather than overproduction of saliva. Botulinum toxin injection into the parotid and/or submandibular glands is the most evidence-based treatment, rated "clinically useful" by the MDS, with effects lasting 3–4 months per injection cycle. Glycopyrrolate (oral or sublingual) reduces saliva production but causes systemic anticholinergic effects. Ipratropium bromide sublingual spray (1%) is a practical option with fewer systemic effects. Atropine sublingual drops (1%) are used in palliative settings⁽²⁾.

Urinary Dysfunction

Overactive bladder (urgency, frequency, nocturia) is the most common urogenital symptom (40–70%). Antimuscarinics (oxybutynin, solifenacin, tolterodine) are first-line, but their anticholinergic burden is a major concern in PD patients with cognitive impairment. Mirabegron (β3-agonist) offers an alternative without anticholinergic cognitive risk and is increasingly preferred. Trospium (does not cross BBB) may be safer than oxybutynin. Desmopressin nasal spray is useful for nocturia but requires electrolyte monitoring⁽²⁾.

Sleep Disorders

REM Sleep Behavior Disorder (RBD)

RBD — characterized by dream enactment behavior due to loss of normal REM atonia — occurs in 30–60% of PD patients and is the strongest prodromal predictor (likelihood ratio >100). In established PD, RBD management focuses on safety (removing sharp objects, padding bed rails, sleeping in separate beds if necessary) and pharmacotherapy. Melatonin (3–12 mg at bedtime) is recommended as first-line due to its favorable safety profile; it reduces RBD episodes without significant sedation. Clonazepam (0.25–1 mg at bedtime) is effective but carries risks of sedation, falls, and respiratory depression in patients with comorbid sleep apnea. The MDS rates clonazepam as "possibly useful" with safety concerns⁽²⁾.

Insomnia

Insomnia — difficulty with sleep initiation, maintenance, or early morning awakening — affects up to 60% of PD patients and is multifactorial (motor symptoms, nocturia, RBD, depression, medication effects). Sleep hygiene is the foundation. Controlled-release levodopa or rotigotine patch at bedtime can improve nocturnal motor symptoms that disrupt sleep. Doxepin (3–6 mg) is useful for sleep maintenance. Eszopiclone has some evidence in PD insomnia. CBT for insomnia (CBT-I) is effective in general populations and is increasingly applied in PD⁽²⁾.

Excessive Daytime Sleepiness

Excessive daytime sleepiness (EDS) affects 30–50% of PD patients and is driven by disease-related neurodegeneration of wake-promoting nuclei, dopaminergic medications (particularly DAs), and disrupted nocturnal sleep. Modafinil (100–200 mg/day) is the most studied agent but received "insufficient evidence" per MDS due to inconsistent RCT results. The first step should be optimizing nocturnal sleep and reviewing medications — dopamine agonists are the most common pharmacologic cause of pathologic daytime sleepiness and sleep attacks⁽²⁾.

Other Non-Motor Symptoms

Pain

Pain is reported by 40–70% of PD patients and is frequently undertreated. It can be classified as musculoskeletal (most common), dystonic (early morning foot dystonia, off-period dystonia), central/neuropathic, or radicular. Optimization of dopaminergic therapy is the first step for fluctuation-related pain. Duloxetine and oxycodone-naloxone (prolonged release) have emerging evidence for PD-related pain. Rotigotine patch has demonstrated pain reduction in PD trials⁽²⁾.

Fatigue

Fatigue is one of the most common and bothersome NMS (reported by ~50% of patients) yet has the least evidence-based treatment options. No intervention has received a "clinically useful" MDS designation. Rasagiline showed a possible benefit in one trial. Exercise remains the best-supported intervention. Methylphenidate and modafinil are sometimes used empirically⁽²⁾.

Apathy

Apathy — reduced motivation, initiative, and emotional engagement independent of depression — affects 15–40% of PD patients. It may worsen after DBS surgery or dopamine agonist withdrawal. Rivastigmine has shown benefit in one small RCT. Piribedil (DA) has preliminary positive data. There is no FDA-approved treatment for PD apathy⁽²⁾.

Pharmacotherapeutic Reference Table