Possible Implications of Managing Alexithymia on Quality of Life in Parkinson's Disease: A Systematic Review

Alexithymia, characterized by difficulty in recognizing and verbalizing emotions, is reported to be more prevalent in subjects with Parkinson's disease (PD) than in the general population. Although it is one of the nonmotor symptoms of PD, alexithymia is often overlooked in clinical practice. The aim of this systematic review is to investigate the prevalence of alexithymia in PD, assess its impact on quality of life, and explore the rehabilitation approaches for alexithymia. Research articles, selected from PubMed, Scopus, and Web of Science, were limited to those published in English from 2013 to 2023. The search terms combined were “Alexithymia,” “Parkinson's disease,”, and “Quality of life.” Current literature review indicates that alexithymia is commonly assessed using the Toronto Alexithymia Scale (TAS-20), and it is associated with deficits in visuospatial and executive functions. Presently, rehabilitation interventions for alexithymia are scarce, and their effectiveness remains controversial. Future research should focus on developing comprehensive assessments and rehabilitation strategies for emotional processing, considering its significant impact on the quality of life of both patients and caregivers.


Introduction
Alexithymia is a personality construct characterized by difculty in identifying and describing feelings accompanied by an externally oriented thinking style marked by a focus on external, observable events rather than internal thoughts, feelings, or fantasies.Individuals with this thinking style tend to concentrate on concrete details and practical aspects of their environment, often at the expense of introspection and emotional awareness [1,2].Some researchers suggest that alexithymia might be a personality characteristic that plays a role in the onset and intensity of somatic and psychological health conditions [1,2].Alexithymia, extensively investigated in neurological conditions [3,4], nonneurological diseases [5,6], and various psychiatric disorders [7,8], is also relevant to Parkinson's disease (PD), a disorder primarily associated with motor symptoms.However, the recognition of PD's nonmotor symptoms (NMS), which signifcantly impact patients' quality of life, is increasing among healthcare professionals and scientists, suggesting a potential area for alexithymia research within this population.Te NMS of PD encompass cognitive impairment [9,10] and neuropsychiatric conditions like apathy [11,12], depression [13,14], and alexithymia [15,16].In addition, there are also REM behavior disorders (RBD) [17], olfactory disfunction [18], fatigue [19], sexual dysfunction [20], gastrointestinal symptoms such as dysphagia and dribbling of saliva.Further, symptoms of dysautonomia in PD may include orthostatic hypotension, bladder dysfunction, gastrointestinal dysfunction (particularly constipation) [21], and hyperhidrosis [20].Te cognitive defcits associated with PD are believed to stem from diminished dopamine activity in the nigrostriatal and mesocortical dopaminergic systems, resulting in the malfunctioning of neural networks, including the basal ganglia and related cortical areas [22].Te reduction of dopamine in key brain regions important for emotional processing, including the anterior cingulate cortex (ACC) and orbitofrontal cortex, might be a fundamental factor in the emergence of alexithymia in this condition [23,24].
Alexithymia's features indicate defcits in both understanding and managing emotions, including challenges in using adaptive strategies for emotional regulation (like adjusting arousal levels, expressing or restraining emotions, and cognitive integration).Tese difculties might also play a role in the progression and trajectory of diverse psychiatric and medical conditions, including depression and diabetes [8,25], and can infuence the efectiveness of treatment [26,27].
Jacobs et al. [28] discovered that PD subjects showed reduced performance in tasks related to emotional facial imagery, as well as in tasks involving emotional expression and recognizing emotions in faces.Dujardin et al. [29] also found that PD subjects have difculty interpreting facial emotions at earlier stages of the disease.Furthermore, Simons et al. [30] observed that, compared to healthy controls, PD subjects had more difculty in posing emotional facial expressions.Studies focusing on the ability to recognize and express afective verbal expressions have similarly highlighted defcits in PD subjects regarding communication and emotions interpretation [28,31].
In the current literature, there is variability in sociodemographic aspects such as age, sex, and education in relation with alexithymia in PD.Indeed, research has indicated that factors like age are linked to alexithymia [3,32], while male gender may infuence the expression of alexithymia [32,33].However, not every study has established a meaningful connection between gender and alexithymia [3], suggesting that factors beyond gender are more predictive of alexithymia [34].
Furthermore, higher levels of education appear to be inversely related to alexithymia [3,35].Previous studies found a link between lower education level and challenges in recognizing emotions [3], highlighting lower education as a potential risk factor for alexithymia [36,37].
Quality of life (QoL) is a complex, multifaceted concept encompassing at least three major areas: physical, mental, and social well-being.Within the medical realm, the notion of health-related quality of life is frequently employed by researchers and clinicians.Tis concept particularly focuses on how an illness and/or its treatment infuences a patient's self-perceived health status, as well as their subjective sense of well-being or life satisfaction [38].In PD people, subjective elements infuencing QoL encompass their perception of symptoms, physical ftness, self-image, contentment with family life, occupational satisfaction, fnancial circumstances, interactions with others, social support, and overall life experience.Te objective factors contributing to QoL in PD include the clinical manifestations of the disease, social standing, living conditions, and the extent and intensity of social interactions [39].QoL in PD is infuenced by both motor symptoms (tremor, rigidity, bradykinesia, postural instability) and nonmotor symptoms (anxiety, sleep disturbances, autonomic dysfunctions) [40].Disability level, daily activity dependence, and the presence of depression and cognitive decline signifcantly afect QoL [41].Social factors, including socioeconomic status, living conditions, access to healthcare, and support services, as well as the quality of social interactions and support from family and friends, are also crucial [42].In addition, the efectiveness and side efects of pharmacological interventions play a critical role in determining QoL in PD patients [43].
Given the limited research on alexithymia in PD, this review aims to explore its impact on QoL in PD population and to identify existing rehabilitation approaches for alexithymia.

Search Strategy.
Te systematic review was performed using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) [44] guidelines to investigate alexithymia in PD, focusing on the impact on QoL and rehabilitation approaches for alexithymia.Tis systematic review did not involve human nor animal data collection.Terefore, ethical approval was not required.

Study Selection.
After the removal of the duplicates, all the articles were evaluated based on the titles and abstracts by three of the researchers (LC, VLB, and CF), independently.Tese researchers read the full-text articles deemed suitable for the study, and performed data collection to reduce the risk of bias.Any disagreement was discussed by the three above authors.
Te inclusion criteria were (a) subjects with PD and alexithymia and (b) PD subjects treated and not treated with deep brain stimulation.Te exclusion criteria were (a) atypical Parkinsonism and (b) article not written in English.
Electronic searches identifed 445 papers.We rejected 121 studies because they were duplicates.After reading the full text of the selected publications and applying the predefned inclusion criteria, we excluded 277 articles based on title and 12 on abstract; 12 because they did not focus on alexithymia in PD and 11 because they were review.After an accurate revision of full manuscripts, 12 articles satisfed the inclusion/exclusion criteria (Figure 1).

Results
Te exploration of the relationship between alexithymia and PD has gained signifcant attention in recent research (Table 1).Based on the reviewed studies, the prevalence of alexithymia in PD varies considerably across diferent cohorts.Sengul et al. [45] reported a prevalence of 35% for alexithymia, with an additional 33% of patients classifed as borderline alexithymic.Similarly, Alvarado-Bolaños et al. [46] found a higher prevalence rate of 56% in their PD sample.Goerlich Dobre [47] reported that 18% had clinical alexithymia, and 26% had moderate alexithymia.Te distribution of alexithymia across age and gender shows that male patients are more frequently afected.Kenangil et al. [45] reported a higher prevalence of alexithymia in males compared to females within their cohort, where the mean age was 60.33 years.Sengul et al. [48] also observed a mean age of 71.2 years with a higher proportion of male patients (62.8%).In terms of disease stage, Kenangil et al. [45] identifed signifcant diferences in Hoehn and Yahr (HY) stages between alexithymic and nonalexithymic PD patients, with higher HY stages correlating with increased alexithymia prevalence.Alvarado-Bolaños et al. [46] supported this fnding, indicating that alexithymic patients were more likely to be in advanced HY stages.Te study by Bogdanova et al. [49] found a signifcant correlation between alexithymia ratings and disease stage, indicating that higher disease stages are associated with higher alexithymia levels.On the contrary, Sengul et al. [48] did not fnd a signifcant correlation between H&Y stages and alexithymia.Te prevalence and characteristics of alexithymia in PD vary across diferent stages and treatment modalities.Alvarado-Bolaños et al. [50] reported that alexithymia in early PD patients treated pharmacologically is associated with both motor and nonmotor symptoms.However, they did not provide a detailed analysis of how specifc pharmacological treatments infuence alexithymia, highlighting the need for further investigation.In patients with moderate PD and motor and nonmotor fuctuations, the literature lacks detailed information on the characteristics and frequency of alexithymia, underscoring the necessity for future studies to diferentiate between these subpopulations.Castelli et al. [51] observed that Deep Brain Stimulation (DBS) did not signifcantly alter alexithymia levels compared to pre-DBS patients.Tis suggests that alexithymic symptoms may persist in advanced PD stages, irrespective of surgical Parkinson's Disease  Parkinson's Disease interventions, pointing to the need for additional therapeutic strategies.Alvarado-Bolaños et al. [50] also emphasized that longer disease duration and more severe motor symptoms are associated with higher levels of alexithymia.Tis implies that as PD progresses, the severity of alexithymic symptoms increases.In contrast, Goerlich-Dobre et al. [52] found no signifcant correlation between alexithymia scores and disease duration or dopaminergic medication dosage, such as total levodopa equivalent daily dose (LEDD) or dopamine agonist LEDD.Tese conficting fndings highlight the need for further research to clarify the relationship between disease duration, symptom onset, and alexithymia.Klietz et al. [53] focused on the impact of alexithymia on both people with Parkinson (PwP) and their caregivers.Employing disease-specifc questionnaires, they discovered a notable correlation between alexithymia in PwP and reduced health-related quality of life (HR-QoL), with specifc aspects like difculty in identifying and describing feelings being particularly infuential.Caregiver burden was also signifcantly associated with alexithymia in PwP, particularly with aspects of alexithymia like external-oriented thinking and identifying feelings.
Furthermore, Castelli et al. [51] investigated the impact of DBS on alexithymia in PD subjects.Tey compared groups undergoing STN-DBS with those who did not, fnding no signifcant diference in alexithymia levels post-DBS, though both groups exhibited higher alexithymia than controls.No signifcant correlation was found between alexithymia and the severity of Parkinson's disease.In a related longitudinal study, Dafsari et al. [49] reported a signifcant decrease in alexithymia prevalence and improvements in QoL and motor symptoms following STN-DBS with a signifcant reduction in the levodopaequivalent daily dose (LEDD).
Further exploring the broader implications of alexithymia in PD, Gul et al. [46] linked high levels of alexithymia with cognitive decline in PD patients, identifying alexithymia as a signifcant predictor of cognitive performance.Tis was supported by Bogdavona et al. [48], who found a correlation between alexithymia and nonverbal cognitive tasks, suggesting a deeper connection with certain cognitive functions.Notably, the severity of alexithymia, but not apathy or depression, correlated with the Hoehn and Yahr index of PD disease stage.
Te recent study by Alvarado-Bolanos et al. [50] aimed to identify determinants of alexithymia in PwP, linking it with factors like education level and urinary symptoms.Tey also emphasized the impact of alexithymia on the QoL in PD.
Sengul et al. [45] associated alexithymia with poorer performance in visuospatial and executive function tests and depressive symptoms, highlighting the complex interplay between alexithymia and cognitive dysfunctions in PD.Kenangil et al. [54] added to this by noting a correlation between the F3 subscale of Toronto Alexithymia Scale (TAS-20) scores and Montreal Cognitive Assessment (MOCA-TR) scores, indicating a link between alexithymia and cognitive functions.Tere was no signifcant diference in depression levels (BDI scores) between PD subjects and controls.Te study did not fnd a relationship between alexithymia and the duration of PD or total levodopa dose.
Te impact of PD on emotional processing was further detailed by Enrici et al. [47], who noted signifcant defcits in emotion recognition, representation, and regulation in PD population, particularly in interpreting facial expressions and social cues.Tis impairment was distinct from any general cognitive of psychiatric status, including depression, anxiety, or apathy.
Lastly, Goerlich-Dobre [52] and Sonkaya et al. [55] provided unique perspectives.Goerlich-Dobre et al. [52] showed that alexithymia, especially difculties in identifying and describing feelings, is linked with impulse control disorders in PD.Sonkaya et al. [55] emphasized the relevance of alexithymia as a nonmotor symptom in PD, correlating it with the severity of motor symptoms.

Alexithymia and Comorbidity in PD: Te Impact on
Quality of Life.In this systematic review, we explored the impact of alexithymia on the QoL of people with PD.Te distress/protection model defnes QoL as the overall balance between protective and distressing factors [56] where the prevalence of distressing factors (such as severe depressive symptoms) over protective factors (such as family social support) results in lower QoL.Te presence of both motor and psychosocial dysfunctions and psychiatric comorbidities in PD patients can lead to a decrease in their QoL [57][58][59][60][61].
Te impact of NMS on HRQoL has been examined in some longitudinal studies, showing that the nonmotor symptoms signifcantly increase over time afecting the quality of life [61][62][63].Tis might apply specifcally to the socalled honeymoon period, when patients are adequately pharmacologically compensated from the motor perspective [49,62,64,65].
Numerous studies increasingly focus on NMS as outcome measures, but they do not always assess their impact on HRQoL and caregivers' burden [66,67].
A single study assessed the QoL of caregivers of Parkinson people using the Parkinson's disease caregiver burden questionnaire (PDCB) [53].Tis evaluation is crucial because neuropsychiatric symptoms can disrupt familial and social dynamics, leading to nursing home placement, and having severe negative efects on patients' HRQoL and caregivers' burden [65].According to previous fndings, the studies included in this systematic review suggest that NMS, particularly alexithymia, are signifcant contributors to HRQOL [62,68].
Alexithymia, characterized by difculties in identifying and expressing emotions, is a notable nonmotor symptom in PD.Te reviewed studies suggest a link between alexithymia and cognitive dysfunction in PD patients, particularly in the domains of visuospatial and executive functions, indicative of frontostriatal and parietal dysfunction in PD [48].
Parkinson's Disease Specifcally, the alexithymia aspect "externally oriented thinking," measured by the F3 subscale of the TAS-20, correlates with the visuospatial domain of the MOCA [54].Bogdanova et al. [48] discovered that higher TAS-20 scores are linked to diminished performance in visual-spatial ability tests, involving emotional stimuli, suggesting a link between alexithymia and right hemisphere dysfunction, as the right hemisphere plays a key role in processing visuospatial information.Furthermore, Sengul's study [45] showed that patients with elevated levels of alexithymia exhibit lower performance in the clock drawing test, a measure of compromised visuospatial function.
Interestingly, alexithymia in PD appears independent of motor neurological symptoms, dopaminergic treatment, and the laterality and type of motor symptom onset [54].Tis suggests that alexithymia may arise from diferent underlying mechanisms than those driving the motor symptoms of PD.A few studies have investigated the link between motor symptoms and alexithymia.In the study by Alvarado-Bolanos [50], a correlation was observed between the intensity of motor symptoms and the severity of alexithymia.Costa et al. [69] noted that the severity of motor symptoms was similar between alexithymic and nonalexithymic people with PD, although the postural instability and gait disorder subtype is linked with greater challenges in recognizing and articulating emotions.
In Addition, Enrici et al. [47] reported that there was no signifcant association between the use of dopamine medication and the presence of alexithymia in people with PD.Similarly, Goerlich-Dobre et al. [52] found no relationship between alexithymia and various factors such as disease duration, total levodopa dose, or dopamine agonists' dosage, suggesting that the use of dopaminergic medications and the progression of neurodegenerative processes in PD do not appear to negatively impact patients' emotional selfawareness.Conversely, some studies have suggested A potential link between alexithymia and PD severity.Sonkaya et al. [55] examined the relationship between alexithymia and Parkinson's disease severity, fnding that higher levels of alexithymia were associated with UPDRS III scores above 30.However, Castelli et al. [51] did not observe a signifcant connection between alexithymia and disease severity.
Te relationship between alexithymia and depression in PD is complex and somewhat conficting.While some studies have found a signifcant correlation between these two conditions [3,70], others suggest that aspects of alexithymia may be independent of depression [54] Tis underscores the multifaceted nature of neuropsychiatric symptoms in PD and their impact on patients' quality of life.
Apathy is another crucial NMS to address in PD due to its substantial impact on QoL and patient disability [71,72].In the study conducted by Bogdanova et al. [48], apathy levels, but not depression, were linked to alexithymia severity.Both alexithymia and apathy are conditions that can be treated, and early detection and intervention might safeguard the QoL and lessen disability in individuals with PD.Furthermore, subjects who have difculty recognizing and understanding their own emotions, and who often suppress their feelings as a way of managing them, may be vulnerable to being overwhelmed by negative emotions that they cannot identify or articulate.In this regard, fndings reveal that not only clinical levels of alexithymia but also moderate levels are signifcantly correlated with a higher incidence of impulse control disorders (ICDs) in PD [52].
Te evaluation of specifc treatment strategies to improve the NMS of Parkinson's disease and, in turn, HRQoL has been limited by few studies.Improvement in NMS was demonstrated by infusional therapies, such as subcutaneous apomorphine and intrajejunal levodopa, but there was no specifc investigation of the impact on HRQoL [73,74].

Te Assessment and Rehabilitation of Alexithymia.
A signifcant methodological concern in PD research is the assessment of alexithymia.Among the analyzed studies, only one employed Bermond-Vorst Alexithymia Questionnaire (BVAQ) [46], a reliable and valid assessment tool including 40 statements rated on a 5-point Likert scale.Tis questionnaire encompasses fve subscales that cover both cognitive and afective aspects of alexithymia.Te subscales of fantasizing and emotionalizing concern the afective dimension, while identifying, analyzing, and describing subscales represent the cognitive dimension.Te total score can range from 40 to 200, with higher scores indicating greater levels of alexithymia [75,76].Te internal consistency for the total BVAQ score and certain subscales (Verbalizing, Identifying) is acceptable (Cronbach's alpha around 0.70-0.80).However, some subscales (Fantasizing, Emotionalizing) exhibit lower internal consistency [76].Most studies have employed the TAS-20 [77], a self-report questionnaire designed to measure alexithymia's three primary aspects: difculty in identifying and describing feelings, and a tendency towards externally oriented thinking.Participants rate their agreement with 20 statements on a 5-point Likert scale.Te TAS-20, widely adopted in both clinical and nonclinical populations, is considered to have strong convergent and discriminant validity [77].Te reliability of the total scale equals 0.81, and the reliabilities of the three factors are 0.78, 0.75, and 0.66 (F1, F2, F3, respectively) [77].In addition, the TAS-20 has shown good test-retest reliability.However, its psychometric properties specifc to PD subjects remain unexplored, presenting a potential limitation for two key reasons.Firstly, accurately responding to the TAS-20 requires meta-cognitive abilities, which might be compromised in PD subjects due to possible reductions in executive function efciency.Indeed, executive performance has been shown to correlate with TAS-20 scores [48].
Secondly, completing the questionnaire necessitates intact self-awareness.Tis challenge extends to all self-report assessments that require individuals to evaluate and recognize their cognitive and emotional traits.Prigatano and Schacter [78] describe self-awareness as the ability to perceive oneself objectively while maintaining subjectivity.Impairments in self-awareness could therefore infuence TAS-20 responses.Recent studies indicate that selfawareness may be diminished in PD subjects.For instance, Kudlicka et al. [79] observed that PD people with 6 Parkinson's Disease executive dysfunctions had more difculty acknowledging their cognitive impairments compared to those without such dysfunctions.Another study involving PD subjects by Amanzio et al. [80] found a link between awareness of movement disorders and dopamine stimulation.Specifcally, they noted that PD subjects in the "on state" showed reduced awareness of dyskinesia-related motor defcits, which correlates with executive functions, whereas in the "of state," their awareness of hypokinesia remained intact.Terefore, a clear and precise operational defnition of alexithymia in PD is essential for ensuring consistency and accuracy in research.Alexithymia is commonly characterized by difculties in identifying and describing feelings, a limited imaginal capacity, and an externally oriented cognitive style [1,2].In the context of PD, these traits may be compounded by the neurological and psychological challenges inherent to the disease.Te prevalence of alexithymia in PD could potentially vary depending on the screening tool used.Te TAS-20 provides a broad measure, while a dedicated alexithymia scale tailored to the specifc neurological and psychological context of PD might reveal diferent prevalence rates.Tis underscores the need for ongoing research to develop and validate such specialized tools.
In the current landscape of research on PD, there is a notable scarcity of comprehensive studies focusing on both pharmacological and nonpharmacological treatments for alexithymia in PD.Despite the recognized prevalence of alexithymia and its detrimental impact on QoL, there remains a gap in the literature regarding specifc interventions aimed at ameliorating this condition.
Te efectiveness of Subthalamic Nucleus Deep Brain Stimulation (STN-DBS) in treating alexithymia in PD subjects has yielded mixed results.Dafsari et al. [49] contribute signifcantly to this domain by showing that bilateral STN-DBS can positively infuence alexithymia, as evidenced by signifcant improvements in alexithymia scores and reduced prevalence.Tese benefts are closely linked to enhanced QoL outcomes.However, Dafsari et al. [49] also emphasize the necessity for further research to understand the enduring impacts of DBS on alexithymia.Contrastingly, Klietz et al. [53] reported only marginal benefts from STN-DBS in alleviating alexithymia symptoms.Tis study introduces the concept that mindfulness-based interventions could be advantageous for PD subjects.By promoting heightened awareness of feelings and emotions, these interventions might also contribute to an improved HRQoL.Further complicating the picture, Castelli's study suggests a neutral efect of STN-DBS on alexithymia in PD, neither signifcantly improving nor exacerbating it.Te persistently high prevalence of alexithymia among both DBS and pre-DBS groups underscores the need for an integrative approach to PD management that includes psychological components.Tis is particularly relevant considering the association between STN-DBS and increased risks of suicide [81], and the higher prevalence of suicidal thoughts among individuals with alexithymia [82].
In populations without PD, mindfulness practices have shown potential in modifying alexithymic tendencies [83].While alexithymia often poses a challenge to successful psychotherapy, mindfulness-based methods have shown efcacy in ameliorating this condition.Tese approaches could be advantageous for PD subjects and their caregivers, potentially enhancing their HRQoL.However, the efectiveness of such interventions in PD people might be limited due to attentional cognitive defcits typical in this population.Terefore, established programs like mindfulnessbased stress reduction might ofer valuable insights into the efects of mindfulness on alexithymia in PD.Klietz et al. [53] also highlight the signifcant role of mindfulness in caregivers, underscoring its potential to alleviate caregiver burden.
Te presence of alexithymia in PD people has implications for their care [53].Understanding and addressing this condition could lead to better management strategies, potentially improving the QoL of this population.Tis involves considering the broader neuropsychiatric context of PD, including cognitive and emotional aspects, beyond the primary motor symptoms.
In summary, the studies reviewed collectively underscore the multifaceted impact of alexithymia on PD patients, infuencing aspects from QoL and cognitive functions to emotional processing and impulse control.A notable limitation in these studies is the absence of control groups.In addition, there is a pressing need to standardize alexithymia rehabilitation approaches to improve patient's quality of life.

Limitations
Te main limitation of the present review is that the process of selection and recruitment of PD patients varied across the studies selected, raising concerns about the representativeness of the samples.In terms of cognitive performance, although many studies required Mini Mental State Examination (MMSE) scores of >26 or 28 for inclusion [47,48], some studies report that alexithymic PD patients often exhibit lower scores on cognitive assessments.For instance, Alvarado-Bolaños et al. [50] observed that alexithymic PD patients scored lower on the MoCA by an average of 1.7 points compared to nonalexithymic PD patients, suggesting that cognitive impairment is more pronounced in the alexithymic group.In addition, Bogdanova et al. [48] found that alexithymia in PD patients was signifcantly correlated with poorer performance on tasks requiring executive and visuospatial processing, such as the Trail Making Test (TMT) and Raven's Coloured Progressive Matrices (RCPM).Tese fndings underscore the importance of considering cognitive impairment when assessing alexithymia in PD patients.
Moreover, many studies had small sample sizes, limiting the ability to explore subgroup efects, such as diferences by motor symptom onset (tremor vs. nontremor) or interactions with gender [46,54].Furthermore, there is no standardized operational defnition of alexithymia in PD, leading to potential underdiagnosis due to the lack of objective diagnostic criteria.Tis variability makes it difcult to compare fndings across studies and to draw frm conclusions.Te role of comorbid conditions such as stroke, cerebrovascular disease, Alzheimer's disease, and Parkinson's Disease PD-dementia has not been adequately evaluated.In addition, many studies did not adequately address the potential impact of pharmacotherapy, including antidepressants and dopaminergic medications, on psychological variables [45,51,53].Tis omission could lead to incomplete or biased interpretations of the data.
Longitudinal studies are needed to better understand the temporal relationship between alexithymia and PD, and whether alexithymia could be a preceding nonmotor symptom (NMS) similar to sleep behavior disorder or olfactory dysfunction [54].Future research should include neuroimaging studies to determine the neuroradiological correlates of alexithymia and focus on its treatment.Tese studies can provide deeper insights into the brain regions involved and potential therapeutic targets.

Conclusion
Tere is a growing body of evidence suggesting that NMS of PD have a negative impact on HRQoL.However, there is still a small number of therapeutic clinical trials that deal with nonmotor aspects of PD, particularly alexithymia, and their efects on HRQoL.Alexithymia in PD is reported to be higher than in the general population, and it is associated with cognitive impairments, particularly in visuospatial and executive functions and afective disorders such as depression, apathy, and impulse control disorders.Te clinical implication of these fndings is that the best assessment and management of alexithymia could improve the QoL of patients and reduce the caregiver burden.Despite the recognized prevalence of alexithymia and its negative impact on QoL, there is a gap of literature on specifc interventions aimed at ameliorating this condition.Further research is required to establish the best rehabilitation approaches for enhancing patient well-being.

Figure 1 :
Figure 1: PRISMA fowchart showing identifcation and inclusion of studies in the systematic review.

Table 1 :
Te main studies concerning alexithymia in Parkinson's disease.