From Hopelessness to Hope: Addressing Demoralization in Parkinson's Disease

Abstract

Background

Demoralization is a pervasive yet under‐recognized syndrome that manifests as profound hopelessness, helplessness, loss of motivation and purpose, and impaired coping capacity. Affecting over one‐third of individuals in medical and neurological settings and 20–30% of the general population, demoralization is frequently misclassified as depression. However, its distinct phenomenology necessitates precise differentiation, particularly in Parkinson's disease (PD), where it can profoundly impact quality of life (QoL), social engagement, and treatment adherence, potentially contributing to a desire for hastened death.

Objective

To synthesize the limited empirical and conceptual literature on demoralization in idiopathic PD, delineating its prevalence, phenomenology, and clinical–psychosocial correlates, clarifying distinctions from depression and apathy, and deriving evidence‐informed recommendations for screening and intervention.

Methods

A targeted search of MEDLINE, Embase, PsycINFO, and Web of Science (inception–22 May 2025), augmented by manual reference screening, identified eligible empirical and conceptual studies on demoralization in idiopathic PD, which were appraised against predefined criteria and thematically synthesized due to design heterogeneity.

Results

Seven papers were identified that fit the search criteria.

Conclusion

This paper explores the clinical distinction between demoralization and depression in PWP and presents evidence‐based intervention strategies. A compassionate, multidisciplinary, and personalized approach that incorporates the social and psychological aspects of PD may mitigate demoralization, supporting QoL and enhancing functional outcomes throughout disease progression.

Parkinson's disease (PD) is increasingly recognized as a complex neuropsychiatric disorder, as a substantial proportion of people with Parkinson's (PWP) experience depression, anxiety, apathy, suicidality, and psychosis. Historically, PD has been classified as a movement disorder, which may partly explain why these psychiatric symptoms have often been under‐recognized, under‐reported, and under‐treated. ¹ , ² Although awareness of the impact of PD on mental health is improving, substantial gaps remain in our ability to detect and effectively address the challenges PWP face. From the day of diagnosis, PWP may struggle to preserve their mental well‐being, their sense of mastery and autonomy, and perceived control over their future. The PWP can be immediately thrust into chaos and upheaval upon being diagnosed with PD, like a “bomb went off in their life,” resulting in potentially devastating reactions. These reactions may result in demoralization, a syndrome characterized by a pervasive sense of hopelessness, helplessness, loss of motivation and purpose in life, and inability to cope effectively. ³ Additionally, as the disease progresses, the frustration of enduring persistent and intrusive PD symptoms without relief, coupled with diminishing hope for improvement and the resultant feelings of stigma and isolation, can lead to demoralization and increased suffering.

Demoralization differs fundamentally from depression in both symptoms and treatment. Unlike depression, which often responds to antidepressant medications, demoralization typically requires interventions such as psychotherapy, which support coping skills and address the underlying loss of meaning and purpose. ³ This distinction is crucial for effective treatment because the use of antidepressants alone may fail to alleviate the core symptoms of demoralization.

Although a unique construct, demoralization often overlaps with depression, which affects up to 50% of PWP and can obscure clear identification and appropriate interventions for demoralization. ⁴ Despite their similarities, however, these conditions do not always co‐occur. A study of 245 medical patients with various disorders found that 44% of patients with major depression did not meet the criteria for demoralization, and 69% of those with demoralization did not meet the criteria for a major depressive episode. ⁵ These data highlight the importance of effective screening for both conditions and increasing the awareness of demoralization in both clinicians and PWP. See Figure 1.

“There's a certain inevitability about Parkinson's. A condition that takes more and more from me each day. Over time, impacting every part of my life and perhaps more cruelly, the lives of those around me. There's no escape, no respite, and no notion of getting better. The constant ebbing away of both my physical and mental state is all too real. The onset of new symptoms and the worsening of old ones, act as a constant reminder. It's a surreal feeling, being an observer of my own ‘decline.’ Comparing ‘what was’ with ‘what is’ and fearing ‘what will be’ … all the while feeling helpless to stop it.” Kuhan

Figure 1.

Potential model of demoralization in PD.

Methods

Search Strategy and Study Identification

A targeted literature search of MEDLINE (PubMed), Embase, PsycINFO, and Web of Science was conducted from database inception to May 22, 2025. Search strings combined controlled vocabulary and free‐text terms for Parkinson's disease (“Parkinson*” OR “parkinsonism”) with demoralization‐related constructs (“demoralization,” “demoralization,” “subjective incompetence,” “hopelessness.”) Reference lists of eligible articles, relevant conference proceedings, and clinical guidelines were hand‐searched to locate additional reports.

Eligibility Criteria

Peer‐reviewed empirical or conceptual papers published in English were eligible when they: (i) examined demoralization, its components, or validated demoralization instruments in adults with idiopathic Parkinson's disease; and (ii) reported original data or substantive theoretical analysis applicable to clinical practice. Studies focusing exclusively on caregivers, pediatric parkinsonism, or other neurological disorders were excluded unless PD‐specific results could be disaggregated. Editorials, narrative commentaries without primary data, and animal studies were also excluded. Seven primary studies met the inclusion criteria.

Synthesis of Evidence

Given the heterogeneity of designs and small corpus of evidence, quantitative pooling was neither feasible nor appropriate; therefore, findings were synthesized thematically. Themes were organized around (i) prevalence and phenomenology, (ii) clinical and psychosocial correlates, (iii) distinctions from depression and apathy, and (iv) implications for screening and intervention. Points of convergence and divergence were highlighted to derive pragmatic recommendations for clinicians.

Demoralization

Demoralization can compromise an individual's sense of self and diminish the capacity to manage stressful events, such as a chronic health condition. ³ , ⁶ Two core aspects, feeling overwhelmed and an inability to cope effectively with that feeling, render demoralization particularly threatening, as the experience (similar to trauma) challenges assumptions about oneself and one's “assumptive world” (eg, beliefs and understandings about how things work in the world). ⁷ Significant changes can accompany the diagnosis of PD and lead to a rapid decline in self‐image, feelings of inadequacy, and a loss of meaning and identity that, when combined, may result in demoralization. This sense of loss begins at the time of diagnosis and continues throughout the disease and affects not only PWP but also their loved ones. See Figure 1.

Elements of Demoralization

Here, we outline three core elements of demoralization and how each relates to the experience of living with PD. See Table 1.

TABLE 1.

Diagnostic criteria for demoralization

An individual's inability or perceived inability to effectively cope with a stressful event; a diminished sense of mastery (SI)

Diagnostic criteria encompass:

Affective symptoms of existential distress, including feelings of hopelessness or a loss of meaning and purpose in life; (eg, My life seems to be pointless); My role in life has been lost; I feel hopeless.

2Cognitive attitudes reflecting pessimism, helplessness, a sense of being trapped, and feelings of personal failure; (eg, I no longer feel emotionally in control, I feel trapped by what is happening to me, I do not cope well with life).

3A lack of drive or motivation to cope differently.

4Associated features of social alienation or isolation and a lack of support; (eg, I feel isolated and alone).

5Allowing for fluctuations in emotional intensity, these phenomena persist for more than 2 weeks.

(i) Subjective Incompetence

Subjective incompetence has been proposed as the clinical hallmark of demoralization and is conceptualized as one's self‐perceived inability to perform necessary tasks and express appropriate feelings in distressing situations. ⁸ The inability to employ effective coping strategies commensurate with the distress experienced remains a key feature of demoralization.

“It's just overwhelming… having to both ‘learn’ and ‘live’ with this condition at the same time. I found myself taking on new information and new feelings, neither of which I fully understood. It's like starting a new job, a huge responsibility but without any of the necessary skills or experience to complete it, let alone someone to guide you. I just switched off. It was an emotional drain.” Kuhan

(i) Meaninglessness

Meaning in life (MIL) typically encompasses three key components: significance (perceived inherent value), purpose (pursuit of valued goals), and coherence (one's life makes sense). ⁹ MIL embodies an intricate network of connections, insights, and interpretations that help individuals make sense of their experiences and formulate strategies for their envisioned future. ¹⁰ Although not all individuals diagnosed with PD experience diminished MIL, the literature suggests that stressful events (eg, a diagnosis of PD) can negatively impact meaning and purpose. ¹¹ As a result of both physical and mental health changes, many PWP face significant changes in their social connections, work, and meaningful and enjoyable activities, contributing to a sense of loss. Accordingly, it is not surprising that MIL has a significant negative correlation with apathy in PWP, ¹² highlighting the prospects of meaning‐based interventions for demoralization.

“When I was diagnosed, suddenly, my life felt foreshortened. I was grieving the loss of my imagined future of retirement with travel and relaxing, seeing my daughter through her life stages, and nurturing grandchildren. Suddenly, my mind was filled with images of what would be instead my life: nursing homes and feeding tubes, aspiration, and early death. Neither of these was necessarily true, but in my mind, I had lost something important to me: my future had been snatched away, even though it was never guaranteed in the first place.” Becca

(ii) Hopelessness and Helplessness

Demoralization is characterized by pervasive hopelessness and helplessness. Hope represents a positive motivational state rooted in the belief in one's ability to achieve goals, ¹³ whereas hopelessness reflects a fixed negative outlook and the sense that one's current situation is unchangeable. ¹⁴ This entrenched hopelessness, distinct from depression, is linked to poor health outcomes and increased mortality. ¹⁵ , ¹⁶ The unpredictable and progressive nature of PD exacerbates these feelings, as symptoms vary and worsen over time. ¹⁷ , ¹⁸ Helplessness, a core aspect of demoralization, emerges from a perceived lack of resources to achieve goals, reduced self‐efficacy, and an overarching sense of powerlessness. ¹⁹ In the context of PD, these perceptions can diminish motivation to engage in beneficial activities, such as exercise or social interaction, further perpetuating the demoralization cycle.

Helplessness ensues when one feels they lack the internal or external resources to achieve their goals, resulting in feelings of incompetence and diminished self‐efficacy (ie, one's belief that they cannot take the actions necessary to reach a desired outcome). ¹⁹ PWP may believe that they have little control over the progression of their disease or that they may not be able to continue engaging in pleasurable activities, which further contributes to reduced motivation to exercise, such as avoidance of social events, resulting in a self‐fulfilling prophecy effect.

“Despite my protests, it felt as though my brain was disengaging from my body, lessening my control. The tremor soon moved into my right arm then my left followed by my right foot and then my left. Stiffening my body in the morning, cramping my feet to the point it was difficult to walk, amplifying my tremor, causing significant upper back and neck pain, and turning my nights into restless exhaustion. There was nothing I could do to escape it.” Soania

Assessing Demoralization

Three primary measures are available to assess demoralization: the categorically oriented DCPR, ²⁰ the dimensionally directed 24‐item Demoralization Scale (DS), ²¹ and the more refined 16‐item version DS‐II. ²² Additionally, the Subjective Incompetence Scale (SIS) ²³ has been used to assess the clinical hallmark of demoralization, but more research is warranted to assess its validity. The current literature does not endorse a specific screening instrument for demoralization in PWP. Drawing from our clinical and experiential insights, we advocate for the DS‐II as a valuable tool for clinicians to identify and monitor demoralization in PWP. The DS‐II, which has been psychometrically validated in a palliative care setting, comprises a concise set of 16 items. This brevity facilitates independent completion by patients, rendering it especially suitable for clinical environments where time is limited.

PD and Demoralization

The prevalence of demoralization in PWP is estimated at nearly 20%, notably higher than that observed in age‐ and sex‐matched controls. ²⁴ , ²⁵ , ²⁶ While research on demoralization in PWP is scant, ²⁴ emerging patterns offer some insights. (i) Demoralization is more common in individuals with a younger age of onset of PD, ²⁵ perhaps attributable to the prolonged disease trajectory during their prime years, in contrast to those diagnosed later in life. Cognitive impairments, evident even in the early stages of PD, can disrupt cognitive flexibility, the capacity to adjust behavior according to changing circumstances, and affect emotional processing, thereby exacerbating demoralization. (ii) Early treatment of subjective incompetence may attenuate demoralization and reductions in HrQoL and is likely to improve the course of PD. ²⁷ , ²⁸ (iii) Demoralization frequently co‐occurs with other neuropsychiatric disturbances, a combination that is associated with accelerated decline in both cognitive and motor functioning. ²⁵ (iv) Demoralization may both contribute to and exacerbate depression in PWP. ²⁹ (iii) Lastly, the progressive nature of PD often leads individuals to fear becoming a burden on their caregivers, intensifying the risk of demoralization as the disease progresses. ²⁹

From the moment the PD diagnosis is given, PWP face sudden disruptions in their assumptive world‐ a framework that shapes their understanding of their role in the world, their future, and their sense of meaning and purpose. ³ This may be preceded by distress in the pre‐diagnostic/early symptomatic period, as they may have been seeking an explanation for a disruption in their baseline functioning and awaiting clarity on what is happening to them. PWP may experience a lack of control, uncertainty about the future, and overwhelming confusion about how to navigate their new reality, as PD affects physical abilities and social roles, potentially leading to psychological distress, diminished social engagements, a loss of self‐efficacy, and diminished meaning and purpose. ³⁰ When seeking support from family, friends, the community, or their treatment team, they may feel dismissed or unheard. This perceived lack of support can foster feelings of hopelessness, helplessness, shame, isolation, and self‐stigma may ensue. ³¹ If they isolate and withdraw from society, they can have increased feelings of loneliness, give up on life and others, and have an increased risk of suicidal ideation.

For those diagnosed at a younger age, the effect can be especially destabilizing as it disrupts and upends their sense of a “promised” future at a vital time of productivity and responsibility in life. The importance of the touch point of giving the diagnosis of PD with hope and compassion and offering support from the health care team up front cannot be overstated and, if handled well, may represent a way to positively influence the disease trajectory for the PWP for decades to come. In the words of Schmale, “Most physicians are not aware of the importance patients place on their every word, particularly when they are uttered in a time of health crisis.” ³² Physicians thus have the potential to improve undue pessimism as well as feelings of helplessness and hopelessness.

The subsequent stages of PD are marked by critical crisis points characterized by significant increases in symptoms or loss of function. Transitioning through significant life changes, such as losing a job or resigning due to symptoms, going on disability, giving up driving, and relying on a cane or other mobility devices, entails more than just functional adjustments. These transitions symbolize profound losses of autonomy and independence, and the realization of the permanence of these changes can lead to demoralization.

When assessing the impact of PD, it is essential to consider the combined influence of biological, psychological, and social factors. Biologically, PWP experience a range of motor and non‐motor symptoms that may precipitate social withdrawal and isolation. Psychologically, PD often results in distress, depression, anxiety, anger, shame, and low self‐esteem. ⁷ Socially, PWP may encounter stigma, rejection, social isolation, loneliness, alienation, and unemployment, compounded by possible pre‐existing societal biases related to race, gender, sexual orientation, age, or other cultural and social factors. Additionally, financial challenges remain underexplored in PD, particularly those posed by insufficient financial resources. These insights underscore the necessity for comprehensive assessments and bespoke interventions that proactively target demoralization in PWP.

Women face the intricate challenge of balancing multiple roles, such as parenting, caregiving, and maintaining their careers. This balancing act is notably more pronounced for women with PD, who often strive to fulfill their familial responsibilities despite the limitations imposed by the disease. While research suggests that women with PD may manage their usual activities more effectively than men, this resilience comes at a significant cost. ³³ Women in caregiving roles are likely to experience poorer health outcomes, face challenges in accessing medical care, and have higher rates of depression compared to their male counterparts. Additionally, women with PD typically receive less social support, report lower quality of life, and endure increased emotional distress. ³⁴ , ³⁵ There have also been reports that women have more shame and blame themselves, and often feel unheard and may not complain as much about their symptoms to their providers. ³⁶ These findings indicate that the intersection of gender, caregiving responsibilities, and the psychological burden of PD may play a crucial role in demoralization for women, underscoring the need for targeted research, interventions, and support systems that address their unique experiences.

Treatment Interventions

While addressing PD symptoms is crucial, neglecting the broader experience of the illness can worsen suffering. In this context, suffering emanates from the direct impact of uncontrolled symptoms and the erosion of hope, often beginning at initial diagnosis, and concerns about how one is perceived and treated by others, including the medical team. ³⁷ When clinicians concentrate solely on assessing and treating one specific motor symptom, such as tremor, they risk overlooking the lived experience of PWP. This narrow focus can neglect the complex interaction of social and psychological aspects integral to a patient's well‐being. A holistic approach is essential, one that recognizes and addresses what matters most to the PWP.

The Role of the Treatment Team

Managing Expectations about the Diagnosis

Demoralization may be the result of the diagnosis itself, but it may also stem from confusion regarding the meaning of the diagnosis and its prognosis. ³⁸ Many PWP may struggle to recall much of the conversation on their day of diagnosis after the phrase, “You have PD.” Misconceptions can be about what the diagnosis means for their future, leading to catastrophizing the worst‐case scenario. ³⁹ These challenges can be exacerbated by intolerance of uncertainty, characterized by difficulty managing situations with unpredictable outcomes, which is fundamentally a fear of the unknown that drives anxiety‐related emotional disturbances through a heightened need for control and certainty. ⁴⁰ To address these concerns, it is essential to provide a thorough visit explaining the diagnostic and treatment plan, clarify any misunderstandings, and reinforce the importance of self‐management while answering questions in an empathic manner. ³⁸ Physicians and the treatment team can help alleviate unwarranted pessimism and feelings of helplessness and hopelessness by optimizing symptom management, ensuring a clear understanding of the diagnosis, exploring potential sources of meaning and joy, and encouraging social connections, support, and hope. ³⁹

“In your battle with Parkinson's Disease, knowledge is power, and attitude is everything. You must be an active participant in your disease management, actively seeking solutions to problems that arise and take on a proactive approach to accessing appropriate resources.” Soania

Clinicians play a critical role in screening for, identifying, and treating demoralization in PWP. Inadequate symptom management, insensitive communication regarding progress, failure to actively listen, and dismissive attitudes that devalue the patient can inadvertently worsen demoralization, contributing to invalidation and abandonment. Clinicians must remain engaged and ensure the PWP feels genuinely seen, heard, and supported. Creating an environment characterized by compassion, open‐mindedness, and grounded in culturally competent and trauma‐informed care is essential. Since a profound sense of alienation is often associated with demoralization, each team member's primary focus should be to affirm the patient's intrinsic value through compassionate inquiry and support. ³ Engaging the entire multidisciplinary team can be helpful for effectively addressing demoralization, especially given the time constraints. In addition to psychiatrists, psychologists, and therapists, collaboration with other healing practitioners such as physical therapists (PT), occupational therapists (OT), personal trainers, or mind body practitioners can offer valuable support. However, due to the stigma surrounding mental health, PWP are often reticent to engage with mental health providers on their healthcare teams.

Psychological Support

“Ultimately, I recognized my power to choose optimism over despair. I began to understand that although the diagnosis is simply not within my control, how I face this challenge is ultimately mine to determine, moving me from a position of helplessness to one of true power.” Soania

Wellness strategies that empower patients to make proactive lifestyle choices, including managing medication schedules, optimizing sleep patterns, engaging in regular physical activity, and prioritizing nutrition, are essential. Integrating mind–body practices and fostering social connections further support holistic well‐being by addressing both physical and mental health needs. By establishing structured daily routines and incorporating activities such as yoga, Tai Chi, or mindfulness practices, PWP can regain a sense of control and reinforce their sense of agency. Demoralization, marked by helplessness and hopelessness, can confine individuals to monotonous daily routines and limit their willingness to pursue new experiences. ⁴¹ The sense of confinement and uncertainty can lead to a perception of powerlessness to alter their circumstances, leaving individuals unable to break free from the situation.

Interventions that promote resilience and instill hope are vital, as demoralization tends to improve when either coping skills are employed or stressors are removed (See Fig. 2). ⁴² Healthcare providers can assist in establishing bespoke coping strategies through tailored insights, teaching adaptive strategies (eg, mind–body approaches, community support), and providing resources to help PWP navigate challenges. Through open communication and individualized support, PWP can cultivate robust coping strategies, empowering them to manage distress, enhance resilience, and improve overall well‐being. Therapeutic approaches such as Individualized Meaning‐Centered Psychotherapy (IMCP), ⁴³ Acceptance and Commitment Therapy (ACT), ⁴⁴ and the combination of Cognitive Behavior Therapy (CBT) with Well‐Being Therapy (WBT) ⁴⁵ have shown promise in reducing demoralization and improving psychological well‐being. However, further research is needed to validate these treatments in PWP.

“Take control of those variables that are within your control. I may not have control over my diagnosis or my symptoms much of the time, but I do have control over certain aspects that if optimized, can improve my life experience. Develop a routine that optimizes your physical, emotional, and spiritual health. And recognize that for those of us with a chronic disease like Parkinson's, adhering to that schedule of a self‐care routine is vital.” Soania

Figure 2.

Mediators of demoralization‐the key role of the treatment team. ACT, Acceptance and Commitment Therapy; IMCP, Individual Meaning Centered Therapy; WBCT, Well Being Cognitive Therapy.

Social Support

Demoralization is frequently associated with social isolation and inadequate social support, making interventions such as social prescribing and intentional social network creation potentially effective strategies for mitigating these issues. ² Social prescribing enables clinicians to enhance patient well‐being by “prescribing” resources that promote social engagement. ⁴⁶ Referrals to support groups or social workers can facilitate connections with other PWP and provide valuable social interaction.

Research demonstrates that social support can reduce depression, anxiety, and stigma while also improving emotional well‐being, overall life satisfaction, and positive affect in PWP. ⁴⁷ Since demoralization results from the inability to cope effectively, robust social support serves as a buffer against psychological distress by encouraging healthy coping strategies, improving self‐agency, and reinforcing one's belief that one can manage their challenges effectively. ⁴⁸

Caring for someone with Parkinson's disease can be physically, emotionally, and mentally demanding, yet it often brings a profound sense of purpose and meaning. Although the responsibilities may be overwhelming at times, potentially leading to demoralization for the caregiver and, therefore, the PWP, this experience can foster a sense of identity and achievement, helping individuals uncover inner strengths and values that they might not have realized they possessed. Supporting the caregiver alongside the PWP and helping to engage the dyad before demoralization sets in can be impactful.

“My Parkinson's journey has been like a grieving process. Early on, my denial actually served me well but it's only through openness, connection, and a sense of giving back that I've reached some form of acceptance. In that sense, reaching out was the first step to reaching within.” Kuhan

Conclusion

Demoralization transcends the psychological domain, exacerbating mental, physical, and spiritual suffering, increasing the likelihood of treatment non‐adherence, ⁵ and elevating the risk of suicide. ⁴⁹ Treatment modalities that clarify the realities of a PD diagnosis and empower individuals to actively cope with challenges are likely to be effective in addressing demoralization. Further research is needed to understand the intricate interplay between PD and demoralization, allowing for more targeted interventions aimed at enhancing the QoL of individuals living with PD and perhaps neurodegenerative diseases in general.

A holistic, proactive, patient‐centered approach is essential for effectively managing demoralization. Clinicians, multidisciplinary team members, care partners, and friends play key roles in supporting the PWP by recognizing and validating their experience of demoralization. Peer support from other PWP can help provide real‐life examples of how to live well and even thrive with PD. The compassionate approach of the treatment team during the critical touch point of giving the diagnosis of PD and at other key transition points in the disease trajectory represents a highly impactful opportunity to help pave the way for the best possible outcome for the PWP and to provide hope.

“I defy anyone with Parkinson's not to feel demoralized at times. It's inherent to the condition. Parkinson's after all is just as much about mood and motivation, as it is movement. If this was better understood, I suspect people with Parkinson's would be more accepting of the condition… and perhaps more forgiving of themselves. Despite the challenges (or maybe because of), I remain in awe of those living with this condition and take both comfort and inspiration from them. Over the years I've learnt that when it comes to a Parkinson's journey, its simply… ‘ok not to be ok.’” Kuhan

Author Roles

(1) Research Project: A. Conception, B. Organization, C. Execution. (2) Manuscript Preparation: A. Writing of first draft, B. Review and Critique.

B.M.: 1A, 1B, 1C; 2A, 2B

I.S.: 1A, 1B, 1C; 2B

E.B.: 1C, 2B

G.P.: 1A, 2B

K.P.: 2B

S.M.: 2B.

R.M.: 2B.

Disclosures

Ethical Compliance Statement: Neither Institutional Review Board approval nor informed patient consent were necessary for this work. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines.

Funding Sources and Conflict of Interest: No specific funding was received for this work. The authors declare that there are no conflicts of interest relevant to this work.

Financial Disclosures for the Previous 12 Months: GP has consulted for Acadia Pharmaceuticals, Inc. and GE Healthcare. IS received a speaker honorarium from Acorda. The rest of the authors declare there are no additional disclosures to report.

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.