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Abstract

Parkinson’s disease is the most prevalent neurodegenerative disease, and its incidence is expected to increase in coming years. This review evaluates the psychometric properties and potential utility of the SEND-PD scale in assessing the neuropsychiatric disorders associated with Parkinson’s disease, with a particular focus on their impact on the quality of life of people with the condition. An extensive literature search was conducted from October 1st to 30th 2024, using PubMed, Google Scholar, and ScienceDirect with the keywords: Neuropsychiatric symptoms OR Cognitive impairment OR Cognitive decline AND SEND-PD AND Parkinson’s disease OR Parkinsonian syndromes. Inclusion criteria were English-language articles focused on the psychometric validation, clinical use, or comparison of the SEND-PD scale in populations with Parkinson’s disease. Studies unrelated to Parkinson’s disease or assessment tools were excluded. Boolean operators, language filters, and a 10-year publication window were applied. The SEND-PD scale facilitates early detection and management of neuropsychiatric complications in Parkinson’s disease. Its strength lies in identifying early cognitive impairment, enabling timely interventions such as cognitive rehabilitation and medication adjustments. The SEND-PD is a valuable tool that supports ongoing monitoring and treatment optimization for people with Parkinson’s disease, by providing objective evidence of cognitive changes over time.

Keywords

Neuropsychiatric symptoms cognitive impairment neurodegenerative disease Scale for evaluation of neuropsychiatric disorders in Parkinson’s disease (SEND-PD)Parkinson’s disease clinical application cognitive decline

1 Introduction

Parkinson’s disease (PD) is one of the most common chronic neurodegenerative disorders, and its incidence is expected to double over the next 30 years. Despite increased awareness, early and accurate diagnosis remains challenging. Recent advances such as refined diagnostic criteria and identification of genetic subtypes have shifted PD from a purely clinical diagnosis to one incorporating biomarkers, genetic profiling, and imaging [1]. As well as the well-known motor symptoms, PD is now understood to involve a broad range of non-motor manifestations. For example, neuropsychiatric symptoms, including personality changes and neurochemical alterations, are key features of disease pathology [2]. Studies suggest anxiety, depression, and apathy reduce quality of life (QoL) and may predict early cognitive decline and mild cognitive impairment (MCI) in people with PD [3].

Neuropsychiatric symptoms, though often overshadowed by motor symptoms, are highly prevalent and often the most distressing aspects for those with the condition and their caregivers. These symptoms contribute significantly to functional decline, caregiver burden, and poor clinical outcomes [4]. For instance, people with PD experience an estimated 40 cases of psychosis per 1,000 person-years [5]. Those not receiving levodopa are especially vulnerable to subtypes of anxiety, including panic disorder, social anxiety disorder, and generalized anxiety disorder [6]. The expression and progression of these symptoms may vary by age of onset. People with early-onset PD typically exhibit slower cognitive decline, while late-onset PD is associated with faster deterioration and more depression and anxiety [7]. This heterogeneity underscores the need for systematic assessment tools.

Several standardized instruments have been used in cross-sectional studies to quantify the psychiatric burden of PD. These include the General Health Questionnaire (GHQ-12), Composite International Diagnostic Interview (CIDI), Hamilton Anxiety Rating Scale, Neuropsychiatric Inventory (NPI), Hospital Anxiety and Depression Scale (HADS), and Epworth Sleepiness Scale (ESS). Findings from these tools indicate notable prevalence rates of neuropsychiatric symptoms, including cognitive impairment (13.3%), anxiety disorder (24.5%), agoraphobia (4.9%), social phobia (8%), [8] generalized anxiety disorder (30.8%) [9], panic disorder (22%), apathy (12.7%), and depression (13%) [10]. These values are summarized in Figure 1. Given the burden of these symptoms, this review aims to examine the psychometric evidence supporting SEND-PD’s role in assessing neuropsychiatric symptoms and its potential to improve clinical evaluation and QoL.

Figure 1

Graph showing the prevalence of neuropsychiatric symptoms in people with Parkinson’s disease.

2 Methodology

This narrative review aims to examine the available psychometric evidence on the SEND- PD scale in assessing neuropsychiatric symptoms in PD, especially on its preliminary potential utility and relevance to clinical outcomes. A comprehensive literature search was conducted across PubMed, Google Scholar, and ScienceDirect from October 1st to October 30th, 2024. Search terms included combinations of the following: Neuropsychiatric symptoms, Cognitive impairment, SEND-PD, Scale for Evaluation of Neuropsychiatric Disorders in Parkinson’s Disease, Parkinson’s disease, and Parkinsonian syndromes, using Boolean operators to refine the results.

Articles were eligible for inclusion if they were published in English within the past 10 years and addressed the development, validation, application, or comparative analysis of the SEND-PD scale in PD populations. Articles were also included if they explored psychometric tools for neuropsychiatric evaluation in PD. Non-PD-specific studies and articles unrelated to neuropsychiatric assessments were excluded. The studies included were a mix of cross-sectional studies, cohort studies, validation studies, systematic reviews, pilot studies, and expert opinion papers. A total of 59 references were cited, representing diverse evidence relevant to the scale’s potential clinical relevance. The selection was based on relevance to the objectives of the review rather than a rigid screening protocol.

3 Addressing The Global Burden Of Parkinson’S Disease: Public Health Implications, Scalable Interventions, And Preventive Strategies

The public health impact of PD has grown significantly over the past two decades. According to the Global Burden of Disease study, PD is now the fastest-growing neurological disorder worldwide, as measured by deaths and disability- adjusted life years (DALYs). In 2019, PD was responsible for 5.8 million DALYs, a staggering 81% increase since 2000, and an estimated 329,000 deaths, more than double the number in 2000 [11]. A substantial proportion of people with PD live in low- and middle-income countries, where access to medications and specialized neurological care are severely limited. The economic burden is substantial: in the United States alone, total indirect and direct costs reached $51.9 billion in 2017. Unfortunately, there are few economic analyses from low- and middle-income countries, leaving gaps in global planning and policy formulation [12].

The epidemiology of PD also varies across regions and populations. PD affects all racial and ethnic groups, but incidence and prevalence rise with age. In some parts of the world, such as the Western Pacific, people with PD demonstrate distinct symptom profiles and lower rates of dyskinesia than Western populations. However, systemic challenges remain. For example, in 28 African countries surveyed, levodopa was covered only partially by insurance in 44% of cases and not at all in 16% [11]. To mitigate these trends, scalable and proactive interventions are essential. One such approach is the early detection and monitoring of neuropsychiatric symptoms using tools such as the SEND-PD scale, which may support clinical assessment and inform timely intervention. However, further validation is needed to confirm its impact on long-term outcomes. Evidence also supports the role of non-pharmacological strategies such as aerobic exercise, which may delay progression from prodromal to the manifest stage of PD and reduce symptom severity [13].

Finally, tackling global disparities in PD management will require integrated care models and comprehensive policy frameworks. The World Health Organization (WHO) emphasizes this need, particularly in low- and middle-income countries. Strategic investment in infrastructure, training, and medication access can significantly improve the quality of care and life for individuals affected by PD around the world [14, ¹⁵].

4 The Send-PD Scale

4.1 An Overview

The SEND-PD scale is a structured clinical tool designed to assess a broad spectrum of neuropsychiatric symptoms in individuals with PD. It evaluates key domains such as mood disturbances, psychotic symptoms, apathy, impulse control disorders (ICDs), and behavioral alterations, each of which is known to influence functioning and QoL in people with PD. Mood disorders, particularly depression, are assessed by the severity and frequency of symptoms such as sadness, hopelessness, and anhedonia, allowing clinicians to gauge emotional well-being and functional impairment. Anxiety is evaluated by the intensity and duration of features such as restlessness, panic episodes, and physiological arousal, all of which contribute to psychological distress and reduced daily functioning.

Cognitive performance is examined through tasks related to memory, recall, and recognition. This enables identification of cognitive deficits that interfere with activities of daily living. The scale also captures psychotic symptoms, including visual and auditory hallucinations. It assesses both the frequency of symptoms and their behavioral impact, offering potential insights for future clinical decision-making [16]. The SEND-PD scale also assesses behavioral concerns such as irritability and aggression. These symptoms are important for targeting behavioral interventions when required. Social withdrawal and reduced verbal engagement are also included, underscoring the need for community and psychosocial support in PD care [16].

The SEND-PD also covers sleep disturbances, often secondary to anxiety, depression, or hallucinations. It assesses altered dream phenomena such as vivid dreams and nightmares, which commonly affect people with PD and contribute to poor sleep quality [17]. The scale does not directly measure QoL, but it offers a holistic perspective by capturing the range and severity of neuropsychiatric symptoms that are closely linked to QoL deterioration in people with PD [18]. Table 1 outlines the symptom domains evaluated by the SEND-PD tool, showing their clinical focus, core aspects, and the functional impact on people with PD.

Table 1

Overview of Neuropsychiatric Domains Assessed by the SEND-PD Instrument

Symptom	Aspect	Description	Focus of Analysis
Mood Disorders	Depression	Assesses the severity and frequency of depressive symptoms, including feelings of sadness, hopelessness, and lack of interest.	Evaluates emotional well-being and functionality.
Anxiety Disorders	Anxiety	Evaluates the presence, intensity, and duration of anxiety symptoms, including worry, restlessness, and panic.	Measures psychological distress and its impact on daily life.
Cognitive Function	Memory	Examines short-term and long-term memory capabilities, focusing on recall and recognition tasks.	Identifies cognitive deficits affecting daily activities.
Psychotic Symptoms	Hallucinations	Identifies experiences of visual or auditory hallucinations, assessing their frequency and impact on patient behavior.	Determines the need for intervention and support.
Sleep Disturbances	Insomnia	Assesses the frequency, duration, and impact of altered sleep.	Evaluates the effect of sleep disturbances on overall health.
Behavioural Issues	Aggression	Evaluates instances of aggressive behaviour, including verbal and physical outbursts, and their triggers.	Assesses safety concerns and potential need for behavioral interventions.
Social Withdrawal	Social Isolation	Measures the extent of social withdrawal and engagement in social activities, identifying barriers to social interaction.	Highlights social support and community engagement.
Emotional Dysregulation	Mood Swings	Assesses the presence and severity of mood swings, including irritability and emotional instability.	Evaluates the impact of mood changes on relationships and daily activities.
Quality of Life	Overall well-being	Evaluates the patientʹs overall quality of life across various domains, by focusing on neuropsychiatric issues.	Comprehensive view of the patientʹs overall health

4.2 Validation And Reliability Assessment

The SEND-PD scale has undergone preliminary psychometric evaluation to determine its reliability, validity, and potential applicability in people with PD. Key aspects assessed include internal consistency, test–retest reliability, content validity, and convergent validity across diverse clinical settings and subgroups. Internal consistency, typically assessed via Cronbach’s alpha, reflects how well scale items measure the same underlying construct. In both the original and independent validation studies, the SEND-PD demonstrated solid internal consistency [19]. Cronbach’s alpha coefficients were reported as 0.73 for the psychotic symptoms subscale and 0.82 for the mood/apathy subscale [19]. These both exceed the generally accepted threshold of 0.7 for acceptable reliability. However, the ICDs subscale showed a lower alpha (0.52), suggesting moderate internal consistency for this domain [19]. Item–total correlation coefficients ranged from 0.40–0.68 for psychotic symptoms and 0.59–0.64 for mood/ apathy, reinforcing the reliability of individual items within these subscales [19]. These figures are similar to findings on other validated PD- specific tools such as the PDQ-39 and PDQ-8, which also show strong internal consistency across multiple QoL domains [20]. These findings suggest that the SEND-PD has acceptable psychometric properties in certain PD-specific domains.

Test–retest reliability evaluates the scale’s stability over time [21]. Direct intraclass correlation coefficients (ICC) for SEND-PD are not widely published. However, research on similar neuropsychiatric and QoL measures in PD, such as the PDQ-39 and PDQ-8, and other tools used in chronic neurological conditions like multiple sclerosis, have reported ICC values above 0.80, which is considered indicative of high temporal reliability [22, ²³]. SEND-PD’s correlations with established tools suggest potential for temporal reliability, although there are no direct ICC data [24].

Preliminary studies suggest SEND-PD has good convergent validity [24]. A monocentric study of 122 people with PD found significant correlations between SEND-PD total scores and scores for other validated scales, including the Movement Disorder Society’s Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) Part I (Spearman’s Rho = 0.655) and the Geriatric Depression Scale-15 (Rho = 0.645). This demonstrates the scale’s ability to reflect the real-world burden of neuropsychiatric symptoms [24]. Partial scores from SEND-PD were also very strongly correlated (> 0.90) with matching items on the MDS-UPDRS Part IA. This further confirms its validity for neuropsychiatric assessment in PD [19]. Beyond idiopathic PD, the SEND-PD has also been applied in people with atypical parkinsonian syndromes, such as progressive supranuclear palsy and multiple system atrophy. The scale proved to be brief and user-friendly in standard cohorts of people with PD, but its applicability to atypical parkinsonism was more limited because of the differing symptom presentations [24].

Content validity is the extent to which a scale covers the full domain of interest and is critical in any disease-specific tool. Studies evaluating VO2 max and other functional measures in PD have shown that rigorous definition of test objectives enhances content validity [25]. A similar approach is required for SEND-PD to ensure comprehensive coverage of PD-related non-motor symptomatology [26]. Finally, responsiveness, or the ability of a scale to detect clinically meaningful changes over time, is an emerging area for SEND-PD. Evidence from long-term PD management studies suggests that several existing scales are valid, but often lack sensitivity to change in early or subtle symptom shifts [27]. SEND-PD’s brevity and specificity may offer advantages for detecting changes, but its responsiveness has not yet been formally established.

In summary, the SEND-PD scale shows solid psychometric credentials, with strong internal consistency (Cronbach’s alpha 0.73–0.82), convergent validity with proven neuropsychiatric tools, and stable performance across settings. Formal test–retest metrics like ICC remain underreported, but indirect evidence supports the scale’s reliability. Its utility in atypical parkinsonism is limited, but it appears to be a concise and potentially useful tool for tracking neuropsychiatric symptoms in idiopathic PD. However, further validation is needed. Table 2 outlines major validation studies evaluating the psychometric properties of the SEND-PD instrument, including study setting, sample characteristics, and reported reliability metrics such as internal consistency and inter-rater reliability

Table 2

Summary of key validation studies of SEND-PD tool

Psychometric Property	Study / Source	Sample Size	Population	Measure Used	Key Findings	Implications
Internal Consistency	Validation studies (19)	Not specified	Idiopathic PD	Cronbach’s Alpha, Item-total correlation	• Psychotic symptoms: α = 0.73 • Mood/apathy: α = 0.82 • ICDs: α = 0.52 • Item-total r = 0.40–0.68	• Good internal consistency for most subscales; • ICDs shows moderate reliability
Test–Retest Reliability	Based on related scales (22, 23); indirect data (24)	N/A	PD, MS (indirect comparison)	ICC (inferred), score stability	• Similar tools (PDQ-39, PDQ-8) report ICC > 0.80; • SEND-PD shows consistent results over time	• Indirect evidence supports stability• Needs formal ICC validation
Convergent Validity	Monocentric study (24)	122	Idiopathic PD	Spearman’s Rho correlation	• UPDRS Part I: Rho = 0.655 • GDS-15: Rho = 0.645 • MDS-UPDRS Part IA: r > 0.90	• Strong correlations confirm validity• Reflects real-world NPS burden
Content Validity	Conceptual framework studies (26)	N/A	Idiopathic PD	Expert review, domain mapping	• Covers major NPS categories • May not fully capture atypical symptoms	• Solid foundation; • future improvements can enhance coverage
Responsiveness	Long-term PD monitoring research (27)	N/A	Idiopathic PD	Sensitivity to clinical change	• Limited formal data • Promising for early/subtle symptom change detection	• Needs further testing in intervention/ longitudinal studies
Applicability in Atypical Parkinsonism	Observational studies (24)	Not specified	PSP, MSA	Clinical usability	• Usable in standard PD • Less effective for atypical profiles	• Valid in idiopathic PD; limited generalizability outside this group

4.3 Subscales of Send-PD

SEND-PD has three subscales, covering psychotic symptoms, mood and apathy, and ICDs. These subscales address important neuropsychiatric domains in PD, which significantly influence supportive care and outcomes for people with PD [28, ²⁹]. Hallucinations are the most common psychotic symptom and affect approximately 40% of people with PD. These symptoms typically emerge as the disease progresses and are often exacerbated by dopaminergic medications, which are the primary treatment for PD. Importantly, these symptoms worsen cognitive function, increase caregiver burden, and reduce the QoL of people with PD. SEND-PD may help with early identification and management by guiding clinicians to adjust medications or make referrals to behavioral therapies [30].

The second subscale covers mood disturbances and apathy, which are common non-motor features in PD. Around 50% of people with PD experience depression, with a similar proportion showing apathy. Apathy is characterized by a lack of motivation, diminished attention during daily tasks, and emotional blunting, all of which impair social and functional engagement. Distinguishing apathy from depression is essential, because they require different treatment: dopaminergic agents for apathy and antidepressants for depression. SEND-PD includes items designed to assess and distinguish between these symptoms, enabling tailored interventions [31]. SEND-PD also evaluates ICDs. Compulsive behaviors such as gambling, shopping, and eating are reported in about 13% of people with PD. Dopamine agonist therapy, used to manage motor symptoms, can overstimulate brain reward pathways, leading to impulsive behaviors. These behaviors often cause financial, relational, and legal problems. Early identification of ICDs using tools such as SEND-PD may support timely interventions [32].

Finally, SEND-PD uses a scoring system from 0 to 4, with lower scores indicating minimal or no symptoms and higher scores suggesting a greater need for clinical attention. The scale is designed to help physicians evaluate psychotic symptoms, mood/apathy, and impulse control in people with PD, and preliminary evidence suggests it may have potential utility in clinical assessment. Overall, SEND-PD provides a structured framework that could contribute to the evaluation of neuropsychiatric symptoms in PD, although further validation is warranted [24].

4.4 Comparative Analysis with Other Assessment Tools

Among the many screening tools developed for PD, SEND-PD is relatively new, and it stands out by focusing on cognitive impairments, which often accompany the diagnosis. Like other neuropsychological tools, SEND-PD has limitations, but it was developed with the intention to detect early cognitive impairments in people with PD and progression in the areas affected most, including executive function, attention, and working memory. However, a clear distinction between SEND-PD and other tools used for PD must be outlined to determine its relevance in clinical practice.

4.4.1 SEND-PD and MMSE

The MMSE is a widely used, time-efficient screening tool for general cognitive assessment, but it has notable limitations in PD. It does not adequately assess executive function, attention, or processing speed, which are the key domains affected early in PD [33, ³⁴]. Tasks like serial subtraction or figure copying may fail to capture subtle deficits, and studies show that up to 67% of people with PD with normal MMSE scores still perform poorly on measures such as verbal fluency and symbol coding [33]. MMSE is also susceptible to ceiling and floor effects, making it less reliable for distinguishing between mild and severe impairment. Its scores can also be confounded by non-cognitive factors such as anxiety, fatigue, and educational background, potentially leading to misclassification or underestimation of cognitive dysfunction [34]. These limitations are particularly relevant in PD, where psychological symptoms may be affected by age, and both age and symptoms can influence performance.

SEND-PD was developed to overcome these issues by targeting domains most affected in PD, such as working memory and executive control [33]. Designed with PD pathophysiology in mind, it may offer improved domain-specific assessment of early cognitive changes in PD. However, there are few direct comparative studies. MMSE may be useful for quick screening in high-volume or time-constrained clinical settings, but SEND-PD may be better aligned with the cognitive domains affected in early PD, particularly in people with executive or attentional complaints [33, ³⁴].

4.4.2 SEND-PD, MDS-UPDRS and TMT

The Movement Disorder Society Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) is widely regarded as the ‘gold standard’ for assessing PD, comprehensively covering both motor and non-motor symptoms [35]. However, its sensitivity to early-stage PD is limited by a significant floor effect. This is particularly true for Part III (motor examination), where many items show reduced precision in detecting the subtle motor changes that are common in the early stages of the disease [36]. This limitation reflects the MDS-UPDRS’s design emphasis on broad coverage rather than granularity in detecting early symptoms.

In contrast, SEND-PD omits motor assessment entirely, but provides a targeted evaluation of neuropsychiatric symptoms such as psychosis, depression, and ICDs, which are often under- recognized in PD [37]. SEND-PD has shown preliminary evidence of convergent validity with the MDS-UPDRS Part IA neuropsychiatric items (r = 0.93). However, it also includes PD-specific cognitive domain assessments such as executive function and working memory, which the MDS- UPDRS does not cover [38]. SEND-PD is less comprehensive overall because of its lack of motor evaluation, but its brevity and specificity suggest potential as a complementary tool, especially for early detection of cognitive and neuropsychiatric changes.

Similarly, the Trail Making Test (TMT) is a well-established instrument for assessing attention, working memory, and executive function [39]. However, its focus on these domains means it overlooks other cognitive areas that are relevant in PD, such as memory and visuospatial skills. Research indicates that TMT performance predicts functional outcomes primarily through sequencing ability rather than cognitive flexibility [37]. SEND-PD overcomes these limitations by covering a broader spectrum of PD-specific cognitive deficits alongside neuropsychiatric symptoms, offering a more holistic early-stage cognitive profile.

In clinical practice, tool selection should fit with the specific goals of the assessment. For example, clinicians might:

1. Use MDS-UPDRS for comprehensive motor and non-motor symptom staging and monitoring disease progression, particularly in the later stages of PD.

2. Use TMT for a focused evaluation of executive function and attention, particularly for research purposes or when carrying out detailed neuropsychological assessments.

3. Choose SEND-PD for rapid, PD-specific screening of early neuropsychiatric symptoms and subtle cognitive impairments, especially when there are time or resource constraints.

4.4.3 SEND-PD, PDQ-39, NPI, and PD-CRS

SEND-PD was designed for efficient detection of a broad spectrum of neuropsychiatric symptoms common in PD, such as hallucinations, depression, anxiety, and apathy. These significantly affect daily functioning. Tools like the NPI assess neuropsychiatric symptoms, but were originally developed for dementia and may not fully capture the specific symptom profile in PD [36]. Similarly, the PDQ-39 and its shorter version, PDQ-8, are valuable for evaluating QoL but do not directly assess cognitive or psychiatric symptoms [40]. These tools are therefore best used alongside others that evaluate cognition and neuropsychiatric features more comprehensively, such as SEND-PD [41].

The Parkinson’s Disease Cognitive Rating Scale (PD-CRS) offers a detailed assessment of cortical and subcortical cognitive functions and is particularly useful for monitoring progression from mild cognitive impairment to dementia. However, its length and complexity can limit routine clinical use, and it may lack sensitivity for detecting early cognitive changes in people with PD but not dementia [42]. By contrast, SEND-PD’s brief, disease-specific design makes it potentially useful for screening early cognitive and neuropsychiatric impairments, striking a balance between comprehensiveness and practicality. SEND-PD has also shown good correlation with the neuropsychiatric items of the MDS-UPDRS, offering a potentially more focused and time-efficient alternative [42].

In clinical practice, selecting the most appropriate tool depends on the specific clinical question. For quick, PD-specific neuropsychiatric screening, SEND-PD appears to be a promising option, although further validation is warranted [24]. When the goal is to assess overall QoL, PDQ-39 or PDQ-8 remain valuable [40]. For detailed cognitive evaluation across different disease stages, PD-CRS is appropriate despite its limitations in early detection [42]. In more complex cases, combining tools such as SEND-PD with PDQ-39 can offer a more comprehensive view of symptom burden and its impact on QoL.

Each assessment tool was developed with a distinct clinical focus. Understanding their strengths and limitations helps clinicians choose the most suitable option, balancing accuracy, feasibility, and scope for addressing individual needs. Table 3 compares the SEND-PD with other commonly used instruments, including the MDS-UPDRS, PDQ-39, MMSE, NPI, PD-CRS, and TMT, across domains such as clinical utility, validation strength and limitations.

Table 3

Comparative Overview of Cognitive and Behavioral Assessment Tools in Parkinson’s Disease

Tool	Clinical focus	Strengths	limitation
SEND-PD	Cognitive impairments in PD	Detects early cognitive impairment, focuses on executive function, attention, and working memory, PD-specific.	Excludes motor impairments, less comprehensive than MDS-UPDRS.
Mini-Mental State Examination (MMSE)	General neuropsychological screening	Low time requirement, widely used.	Prone to ceiling/floor effects, less effective for PD-specific symptoms, influenced by anxiety, fatigue, age, and education.
MDS-UPDRS	Motor and non-motor symptoms	Gold standard for comprehensive PD assessment.	Limited utility in early stages; significant floor effect for subtle motor symptoms.
Trail Making Test (TMT)	Attention, working memory, and executive function	Highly specific to targeted cognitive abilities.	Omits memory and visuospatial skills; not comprehensive for PD cognitive symptoms.
Neuropsychiatric Inventory (NPI)	Neuropsychiatric symptoms	Effective for assessing neuropsychiatric aspects.	Requires additional tools for holistic evaluation.
PDQ-39/PDQ-8	Quality of life (QoL) in PD	Specialized for QoL evaluation.	Not comprehensive; must be used in conjunction with other assessments.
PD-CRS	Cortical and subcortical cognitive functions	Assesses both cortical and subcortical functions.	Less effective for early cognitive changes in non-demented PD patients.

4.5 Clinical Application of Send-PD

The SEND-PD scale shows promise as a useful tool for screening and longitudinal monitoring of neuropsychiatric symptoms in PD, including early cognitive concerns. It can help to detect changes suggestive of MCI. However, it is not a diagnostic instrument. Formal assessment tools such as the Montreal Cognitive Assessment (MoCA) or the PD-Cognitive Rating Scale (PD- CRS) should be used to confirm cognitive decline. This facilitates timely cognitive rehabilitation and medication adjustment, which is particularly important because MCI often progresses to more severe forms, such as Parkinson’s disease dementia. During further follow-up and treatment, SEND-PD may become increasingly valuable in tracking changes in cognitive progress over the course of treatment. It may therefore assist in identifying people at risk of pathological cognitive decline, prompting timely evaluation and intervention [24].

People with PD experience a range of non- motor symptoms, such as autonomic dysfunction, sleep disturbance, pain, cognitive impairment, and other neuropsychiatric symptoms. These neuropsychiatric symptoms are prevalent across all stages of PD, and should therefore be evaluated frequently throughout the course of the disease [36]. This focus may enhance the relevance of SEND-PD in certain clinical decision- making contexts. For instance, clinicians can evaluate cognitive suitability for procedures such as deep brain stimulation, which can exacerbate cognitive dysfunction if not fully suitable. When used with the Geriatric Depression Scale (GDS-15) for neuropsychiatric symptoms, SEND-PD may help to assess prevalent symptoms of PD that are often associated with cognitive decline [43].

4.6 Feasibility and Implications of Adapting Send-PD for Digital Platforms

As the trend toward remote healthcare and digital health solutions grows, there is a compelling rationale to explore adapting the SEND-PD scale into a digital format. Creating a mobile or web- based version could enhance its accessibility, facilitating regular monitoring in both healthcare facilities and home environments. Digital assessments for PD have exhibited significant potential. Mobile applications that use finger tapping, voice analysis, and gait monitoring are now complementing traditional motor assessments and show a strong correlation with clinician-rated instruments like the MDS-UPDRS [44, ⁴⁵]. Digital self-assessment tools have also been useful in documenting non-motor symptoms, lightening the load for clinics while ensuring reliable outcomes [46].

Modifying SEND-PD for these platforms could support early identification of symptom progression and allow real-time data sharing between people with PD and healthcare providers. This is especially beneficial for those with mobility issues or living in rural locations with limited access to specialized medical services. However, there are challenges to moving to a digital format. It is essential to ensure that elderly people can easily use the system, address varying levels of digital literacy, and adhere to data protection regulations like GDPR (General Data Protection Regulation) and HIPAA (Health Insurance Portability and Accountability Act). It is also necessary to conduct validation studies to confirm that the digital version is psychometrically equivalent to the traditional paper-based format.

4.7 Limitations of Send-PD

The SEND-PD scale offers valuable insights into neuropsychiatric symptoms in PD. However, there are several limitations that restrict its broader clinical application. Its primary focus on cognitive and psychiatric symptoms means that it is less comprehensive than tools like the MDS-UPDRS, especially when non-cognitive or motor symptoms predominate [35].

The scale’s utility in atypical parkinsonian syndromes such as progressive supranuclear palsy, multiple system atrophy, corticobasal syndrome, and dementia with Lewy bodies is also limited. This is because of differences in symptom profiles, disease progression, and neuropathology. For example, dementia with Lewy bodies often presents with early and severe visual hallucinations and fluctuating cognition, while multiple system atrophy shows more pronounced autonomic dysfunction and less frequent psychosis [47, ⁴⁸]. Depression, apathy, and irritability are the most common neuropsychiatric symptoms in progressive supranuclear palsy [49]. Progressive supranuclear palsy is also characterized by bradyphrenia, and frontal behavioral changes, which are not fully addressed by SEND-PD. This restricts the scale’s applicability in groups with these forms of PD and increases the risk of misinterpretation [50, ⁵¹].

These distinctions suggest that SEND-PD, developed primarily for idiopathic PD, may not fully capture the distinctive neuropsychiatric features of atypical parkinsonism.

People with atypical parkinsonism often experience more rapid cognitive and behavioral changes. This reduces the sensitivity of tools such as SEND-PD designed for more gradual symptom trajectories [52]. There are limited data on the performance of SEND-PD in these populations, and its diagnostic applicability and psychometric robustness remain uncertain. Further research is needed to evaluate its use in atypical cohorts and explore modifications, such as incorporating items addressing early cognitive fluctuations or syndrome-specific behaviors. These modifications could improve its relevance. Given the diagnostic challenges of atypical parkinsonism, adapting scales such as SEND-PD may aid earlier recognition and personalized care but would require additional validation.

A critical psychometric concern lies in the inconsistent internal reliability across subscales. Some domains have acceptable internal consistency (Cronbach’s α ≥ 0.70), but the ICD subscale falls significantly below this threshold (α = 0.52), undermining the diagnostic accuracy of the overall scale. This low reliability may stem from the limited number of ICD items and their low prevalence in the studied populations (19). For clinical screening, a higher standard (α ≥ 0.80) is generally preferred [36, ⁵³], further calling into question the scale’s readiness for routine use. Compounding this issue, there are no published test–retest reliability metrics such as intraclass correlation coefficients (ICC) to confirm stability over time. This limits the scale’s value for longitudinal monitoring. Its brevity is advantageous for rapid administration, but may reduce sensitivity to subtle or early-stage impairments. Without a structured framework to reliably track neuropsychiatric progression, repeat assessments risk producing fragmented data, making it difficult to accurately capture disease evolution [24].

Finally, SEND-PD validation is limited in scope, with few studies conducted across diverse populations, PD stages, and cultural settings. This restricts the generalizability of findings. Preliminary data therefore show promise, but extensive longitudinal and multicenter studies are needed to definitively establish the scale’s clinical utility, validity, and reliability. In summary, SEND-PD is a useful adjunct in the cognitive evaluation of PD but should not be used as a standalone diagnostic tool. It is probably best used as part of a comprehensive, multidimensional assessment strategy to ensure accurate diagnosis and personalized care.

4.7 Future Research Directions

To enhance the potential clinical and research utility of the SEND-PD scale, future studies should focus on several key areas. First, longitudinal research is needed to better track the progression of neuropsychiatric symptoms in PD over time. Most current studies are cross-sectional and provide limited short-term insights. Longitudinal data could offer deeper understanding of trajectories of symptoms such as hallucinations, depression, and apathy in PD. This might enable earlier identification of deterioration, facilitate personalized interventions, and possibly delay severe symptom onset [43]. Second, validation studies across diverse populations are critical. There is considerable variability in the expression of neuropsychiatric symptoms across ethnic and cultural groups due to genetic, environmental, and psychosocial factors. Current validation studies are primarily based on Western cohorts, which limits the scale’s global applicability. Cross-cultural validation would improve its accuracy and relevance worldwide [54].

It is also necessary to refine the existing subscales. The current SEND-PD framework assesses psychotic symptoms, mood/apathy, and impulse control disorders. However, other prevalent symptoms such as anxiety and sleep disturbances remain unaddressed. Incorporating these domains could enhance the scale’s comprehensiveness [55, ⁵⁶]. Finally, it would be helpful to explore the potential to leverage digital platforms such as mobile applications and telemedicine for SEND-PD administration. These technologies may facilitate remote monitoring of neuropsychiatric symptoms, potentially enabling earlier and more personalized care, particularly for people in rural or underserved areas with limited healthcare access. Future research should evaluate the feasibility and effectiveness of digital deployment and real-time data collection in improving the prognosis of people with PD and optimizing their treatment through timely intervention [57, ⁵⁸].

As digital administration of the SEND-PD scale becomes more prevalent, future research must address its accessibility and validity across diverse groups. Many digital health tools implicitly assume a baseline level of health literacy and technological competence. However, these assumptions may not hold for older adults or individuals from low-resource settings. Evidence suggests that the accuracy and usability of digital psychiatric assessments can be significantly affected by limited eHealth literacy and digital exclusion. To support equitable deployment, validation protocols should include user-centered design, language simplification, and culturally responsive interface adjustments [59]. It is also important to evaluate the scale’s integration within varied clinical environments such as community clinics, telemedicine platforms, and primary care systems. This will ensure consistent diagnostic accuracy and prevent disparities in care.

5 Conclusion

The SEND-PD scale is a valuable tool for assessing key non-motor symptoms in PD, including psychosis, mood disorders, apathy, and impulse control disorders. It facilitates early detection and monitoring of neuropsychiatric symptoms and cognitive changes, enabling timely clinical interventions such as cognitive rehabilitation and medication adjustment. It therefore provides important insights into PD-related cognitive and psychiatric symptoms. However, additional assessment tools are necessary to distinguish these symptoms from those typical of other dementias like Alzheimer’s disease. Overall, SEND-PD supports improved management of PD through ongoing symptom monitoring.

Footnotes

Acknowledgements

None.

Funding

None.

Declaration of Conflicting interests

None.

Data Availability Statement

Data sharing is not applicable to this article as no new data were created or analyzed in this study.

Ethics Statement

Not applicable

Informed Consent

Not applicable.

Authors’ contributions

Jawairya Muhammad Hussain: Conceptualization- Lead, Data curation-Lead, Project administration- Lead, Supervision-Lead, Validation-Lead, Visualization-Lead, Writing – original draft-Lead, Writing – review & editing-Lead; Manahil Mubeen: Conceptualization-Lead, Data curation- Lead, Project administration-Lead, Visualization- Lead, Writing – original draft-Lead, Writing – review & editing-Lead; Saim Mahmood Khan: Conceptualization-Lead, Data curation-Lead, Supervision-Lead, Validation-Lead, Writing – original draft-Lead, Writing – review & editing- Lead; Sara Alauddin: Data curation-Equal, Visualization-Lead, Writing – original draft-Lead, Writing – review & editing-Support; Fatima Bismah Athar: Data curation-Lead, Writing – original draft-Lead, Writing – review & editing- Support; Dua Mehboob Ellahi: Data curation- Equal, Writing – original draft-Equal, Writing – review & editing-Support; Qaima Ali: Data curation-Support, Writing – original draft-Equal; Surraiya Riaz Mahmood Khan: Data curation- Support, Writing – original draft-Support; Zarnab Saleem: Data curation-Support, Writing – original draft-Support.

List of abbreviations

ICDs, Impulse control disorders; MCI, Mild cognitive impairment; MDS-UPDRS, Movement Disorder Society’s Unified Parkinson’s Disease Rating Scale; MMSE, Mini-Mental State Examination; NPI, Neuropsychiatric Inventory; PD, Parkinson’s disease; PDQ, Parkinson’s Disease Questionnaire; QoL, Quality of life; SEND-PD, Scale for evaluation of neuropsychiatric disorders in Parkinson’s disease.

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Utility of the SEND-PD Scale in Parkinson’s Disease: A Narrative Review

Abstract

Keywords

1 Introduction

2 Methodology

3 Addressing The Global Burden Of Parkinson’S Disease: Public Health Implications, Scalable Interventions, And Preventive Strategies

4 The Send-PD Scale

4.1 An Overview

4.2 Validation And Reliability Assessment

4.3 Subscales of Send-PD

4.4 Comparative Analysis with Other Assessment Tools

4.4.1 SEND-PD and MMSE

4.4.2 SEND-PD, MDS-UPDRS and TMT

4.4.3 SEND-PD, PDQ-39, NPI, and PD-CRS

4.5 Clinical Application of Send-PD

4.6 Feasibility and Implications of Adapting Send-PD for Digital Platforms

4.7 Limitations of Send-PD

4.7 Future Research Directions

5 Conclusion

Footnotes

Acknowledgements

Funding

Declaration of Conflicting interests

Data Availability Statement

Ethics Statement

Informed Consent

Authors’ contributions

List of abbreviations

References