Neuroimaging and Pathology Biomarkers in Parkinson’s Disease and Parkinsonism

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In their multi-author manuscript, "Neuroimaging and Pathology Biomarkers in Parkinson’s disease and Parkinsonism”, Cilia et al. summarize the learnings from a course recently held in Milan.

The review is timely and up-to-date, and contains many interesting insights for neurologists and researchers interested in the pathophysiological mechanisms of PD beyond the loss of mesencephalic dopaminergic neurons in the SNpc. The individual sentences are usually also thoughtfully formulated.

Major concerns:

1. A challenge to the reader is the insufficient overall integration of the eclectic collection of various topics and details into an overarching story. In other words, as a reader it is difficult to remain focused and to keep track of the overall picture. The large amount of facts offered deserve to be made widely known, but there is a concern that only few scientists will read the paper from beginning to the end, becoming overwhelmed during the course of their attempt. The authors should thus think very hard to mitigate that challenge, for instance by providing various additional schematic figures and graphs to visualize the provided information. One graph could be a flowchart integrating the data provided in the paper that could be used as a diagnostic tool, or as a decision tree assisting in conclusions which clinical symptoms warrants which assessment, or which collection of specific diagnostic markers. Proven diagnostic tools could be distinguished from those in the experimental phase using different colors. Thus, the outcome of the symposium would be a valuable tool, facilitated by the synergistic contribution of leading experts in the field.
2. Another flowchart could integrate information on mechanisms or correlations, for instance with respect to atrophy in the cholinergic basic forebrain, etc. Another figure could be similar to Figure 2B, but integrating more of the data provided in the manuscript.
3. Moreover, to be able to dive deeper into a specific subject, it would be useful to provide the reader with information on which of the authors provided which expertise. A table would be handy. It could have the authors name in the first column, his expertise in the second column, the title of his lecture at the meeting in the third column, and in the fourth column the section of which he was the main author in the current manuscript.

Minor concerns:

1. Page 3 bottom, the following statement must be better explained: “Dynamic imaging approaches using levodopa or psycho-cognitive challenges can assess endogenous dopamine release, where a 10% reduction in D2 receptor binding suggests a fivefold increase in dopamine levels“.
2. Page 6: It is not clear what “phenoconversion” is supposed to indicate. From the context on page 12 and 15, it might be guessed, but it should either be explained or preferably substituted by a better fitting, less vague expression.
3. Page 7: “In a proof-of-concept translational extension, PET scanning in familial PD due to the A53T mutation in the SNCA gene showed concordance between tracer accumulation, DAT-SPECT uptake reduction, and the symptomatic body side…” It must be made clear whether the imaging data were taken from the midbrain, and whether it is contralateral to the affected body side.
4. Page 11: It is not clear what the statement is supposed to indicate: “… and suggest we should not be dogmatic”.
5. Considering the large number of different abbreviations used, a list of abbreviations at the beginning of the manuscript would be helpful.
6. Page 19: Two grammatical blunders need to be corrected in that sentence: “The recent introduction of sensing-capable devices has expanded our understand of brain physiology in PD and open the field to adaptive DBS…”
7. Page 19: Use the corrected following, more precise sentence: “Local field potentials (LFPs) are reliable and feasible biomarkers of patients’ clinical states, reflecting a range of conditions including misplacement of leads implanted for DBS, motor fluctuations, and the quality and quantity of sleep.
8. Page 19: “gamma” lacks a word like “wave” or “band”.
9. Page 19: The language of the following 4 sentences needs to be corrected and formulated comprehensible: “The crucial issue is whether a precision-based approach can be used to inform patients’ selection. While it’s established that levodopa responsiveness is a good predictor in the short term, patients’ trajectories diverge remarkably after few years, most likely expression of the underlying condition (e.g. genes) as well as comorbidities, particularly brain vascular damage [196]. A systematic review of PD-associated gene and outcome of STN DBS is provided in (Table 1). Other objective source of biomarkers for surgical prediction are network activity evaluated with functional MRI or PET as well as microstructural MRI”…

Author Response

Reviewer#1

In their multi-author manuscript, "Neuroimaging and Pathology Biomarkers in Parkinson’s disease and Parkinsonism”, Cilia et al. summarize the learnings from a course recently held in Milan.

The review is timely and up-to-date, and contains many interesting insights for neurologists and researchers interested in the pathophysiological mechanisms of PD beyond the loss of mesencephalic dopaminergic neurons in the SNpc. The individual sentences are usually also thoughtfully formulated.

AA reply: We thank the reviewer for the general positive comment.

 

Major concerns:

1. A challenge to the reader is the insufficient overall integration of the eclectic collection of various topics and details into an overarching story. In other words, as a reader it is difficult to remain focused and to keep track of the overall picture. The large amount of facts offered deserve to be made widely known, but there is a concern that only few scientists will read the paper from beginning to the end, becoming overwhelmed during the course of their attempt. The authors should thus think very hard to mitigate that challenge, for instance by providing various additional schematic figures and graphs to visualize the provided information. One graph could be a flowchart integrating the data provided in the paper that could be used as a diagnostic tool, or as a decision tree assisting in conclusions which clinical symptoms warrants which assessment, or which collection of specific diagnostic markers. Proven diagnostic tools could be distinguished from those in the experimental phase using different colors. Thus, the outcome of the symposium would be a valuable tool, facilitated by the synergistic contribution of leading experts in the field.

AA reply: We fully agree that the breadth of topics and the density of details may challenge readers in maintaining an overarching picture. To directly mitigate this, we have added a new flowchart figure at the end of the manuscript (Figure 5) that summarizes and operationalizes the course outcomes into a decision-support framework for biomarker selection across real-world scenarios. The flowchart integrates the main domains covered in the meeting (i.e. neurotransmitter dysfunction imaging, in vivo imaging of proteinopathies and neuroinflammation, peripheral/CSF biomarkers of α-synuclein pathology, and imaging for progression/management) into a single stepwise pathway starting from clinical presentation (e.g., uncertain parkinsonism; prodromal isolated REM sleep behavior disorder; cognitive impairment; suspicion of atypical parkinsonism; advanced-therapy selection). To enhance usability, modalities are color-coded by maturity level, clearly distinguishing clinically established tools (green color) vs emerging (orange color) vs emerging/experimental approaches (red color). We believe this figure, developed through the synergistic contributions of the international faculty, converts the symposium content into a practical, durable resource for both clinical and research audiences.

 

2. Another flowchart could integrate information on mechanisms or correlations, for instance with respect to atrophy in the cholinergic basic forebrain, etc. Another figure could be similar to Figure 2B, but integrating more of the data provided in the manuscript.

AA reply: We thank the reviewer for this excellent suggestion, which we believe adds significant value to the manuscript by deepening the mechanistic integration of neurotransmitter-specific dysfunction with clinical correlates. In response, we have added a new figure (Figure 3) specifically focused on the cholinergic and serotonergic systems, modeled stylistically after Figure 2B.

To further enhance clarity and accessibility, particularly for readers less familiar with technical details, we have also included a concise, color-coded Supplementary Table 1. This new table summarizes all biomarkers discussed in the manuscript by domain, modality, clinical/research application, and maturity level, thereby complementing the figures and supporting practical interpretation across disease stages.

 

3. Moreover, to be able to dive deeper into a specific subject, it would be useful to provide the reader with information on which of the authors provided which expertise. A table would be handy. It could have the authors name in the first column, his expertise in the second column, the title of his lecture at the meeting in the third column, and in the fourth column the section of which he was the main author in the current manuscript.

AA reply: We agree and have added a dedicated table (Supplementary Table 2) including author names, expertise, lecture title at the meeting, and section for which they were main author.

 

Minor concerns:

4. Page 3 bottom, the following statement must be better explained: “Dynamic imaging approaches using levodopa or psycho-cognitive challenges can assess endogenous dopamine release, where a 10% reduction in D2 receptor binding suggests a fivefold increase in dopamine levels“.

AA reply: we have rephrased and expanded that paragraph to convey a clearer message.

 

5. Page 6: It is not clear what “phenoconversion” is supposed to indicate. From the context on page 12 and 15, it might be guessed, but it should either be explained or preferably substituted by a better fitting, less vague expression.

AA reply: We agree and we have defined the term at first use (page 3) “In routine practice, clinicians face persistent challenges in differentiating PD from atypical parkinsonism, predicting the conversion to clinically manifest synucleinopathy (i.e., development of parkinsonism and/or dementia fulfilling diagnostic criteria) in individuals with high-risk states (hereafter referred to as “phenoconversion”), such as isolated/idiopathic REM sleep behavior disorder (iRBD), and anticipating individual response or vulnerability to advanced therapies”

 

6. Page 7: “In a proof-of-concept translational extension, PET scanning in familial PD due to the A53T mutation in the SNCA gene showed concordance between tracer accumulation, DAT-SPECT uptake reduction, and the symptomatic body side…” It must be made clear whether the imaging data were taken from the midbrain, and whether it is contralateral to the affected body side.

AA reply: we have revised the figure legend (new it is Figure 4) as follows: (B) Concordance between striatal DAT‑SPECT uptake reduction (upper panel) and [18F]‑C05‑05 accumulation in the midbrain (lower panel), both showing left‑predominant changes contralateral to the right‑dominant motor symptoms, in a patient with familial PD due to the A53T mutation in the SNCA gene. We have additionally rephrased caption of the (A) image for clarity.

 

7. Page 11: It is not clear what the statement is supposed to indicate: “… and suggest we should not be dogmatic”.

AA Reply: We have replaced that sentence and rephrased that paragraph emphasizing biological heterogeneity and the need for multimodal/stratified therapeutic strategies (page 12): “Lessons from AD, where only a few therapeutic approaches such as lecanemab, and donanemab have shown modest benefit, highlight the difficulties in targeting complex neurodegenerative processes, and suggest we should account for biological heterogene-ity, timing of intervention, and target engagement, rather than assuming a single mechanism or therapy will be uniformly effective across patients. [81,82].”

 

8. Considering the large number of different abbreviations used, a list of abbreviations at the beginning of the manuscript would be helpful.

AA reply: We agree with the reviewer and have added an abbreviation list, placed after the Abstract.

 

9. Page 19: Two grammatical blunders need to be corrected in that sentence: “The recent introduction of sensing-capable devices has expanded our understand of brain physiology in PD and open the field to adaptive DBS…”

AA reply: We agree and implemented requested edits “expanded our understanding of brain physiology in PD and opened the field…”

 

10. Page 19: Use the corrected following, more precise sentence: “Local field potentials (LFPs) are reliable and feasible biomarkers of patients’ clinical states, reflecting a range of conditions including misplacement of leads implanted for DBS, motor fluctuations, and the quality and quantity of sleep.

AA reply: Done.

 

11. Page 19: “gamma” lacks a word like “wave” or “band”.

AA reply: Done, it was ‘gamma band’. We thank the reviewer for finding this typo.

 

12. Page 19: The language of the following 4 sentences needs to be corrected and formulated comprehensible: “The crucial issue is whether a precision-based approach can be used to inform patients’ selection. While it’s established that levodopa responsiveness is a good predictor in the short term, patients’ trajectories diverge remarkably after few years, most likely expression of the underlying condition (e.g. genes) as well as comorbidities, particularly brain vascular damage [196]. A systematic review of PD-associated gene and outcome of STN DBS is provided in (Table 1). Other objective source of biomarkers for surgical prediction are network activity evaluated with functional MRI or PET as well as microstructural MRI”…

AA reply: We have rephrased that sentence as follows (page 21): “A major unmet need is precision patient selection for STN-DBS. Although it’s estab-lished that levodopa responsiveness predicts short-term motor benefit, longer-term tra-jectories diverge substantially, likely reflecting underlying biology (including genetic background) and comorbidities such as cerebrovascular burden [196]. Evidence from monogenic PD suggests gene-specific differences in outcomes after STN stimulation (Table 1) [197], and broader frameworks (called ‘surgicogenomics’ in analogy with pharmacogenomic) propose integrating CNS-expressed genetic variation beyond classic PD genes to refine selection and counseling [198]. In parallel, objective predictors are emerging from network-level functional MRI and PET imaging and microstructural MRI, which may inform outcome prediction and risk stratification [199,200].

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript provides a comprehensive synthesis of current advances in biomarker research for Parkinson’s disease (PD) and related parkinsonian syndromes. It integrates neuroimaging modalities (PET, SPECT, MRI) with pathology-based approaches (α-synuclein assays, skin biopsy) and clinical frameworks, offering a translational perspective that is highly relevant for diagnosis, stratification, and trial design. The breadth of coverage—from neurotransmitter dysfunction to co-pathologies and therapeutic implications—makes this report a valuable resource for clinicians and researchers. Paper addresses multiple biomarker domains: dopaminergic, noradrenergic, cholinergic, serotonergic systems, proteinopathies, neuroinflammation, and co-pathologies.

The report is structured into four thematic sections:

• Section 1: Imaging neurotransmitter dysfunction (dopaminergic, noradrenergic, cholinergic, serotonergic).
• Section 2: Molecular imaging of pathology (α-synuclein, tau, amyloid, neuroinflammation).
• Section 3: Pathology-to-mechanism models (seed amplification assays, skin biopsy, co-pathology, brain-first vs body-first framework).
• Section 4: Clinical translation and progression tracking (prodromal stages, resilience, connectomics, MRI biomarkers, management strategies).

The organization is logical and facilitates a progressive understanding from molecular insights to clinical applications.

 Paper includes both imaging and pathology-based approaches, bridging molecular mechanisms with clinical applications. I believe that this paper synthesizes current knowledge on biomarkers in PD.

I have only one suggestion to create a table summarizing biomarkers in PD base on this article would enhance clarity and would have a practical utility. This would be extremely valuable, especially since the article discusses the technical aspects in great detail; such a summary would be incredibly useful for physicians/scientists less familiar with the techniques discussed.

Author Response

Reviewer #2

This manuscript provides a comprehensive synthesis of current advances in biomarker research for Parkinson’s disease (PD) and related parkinsonian syndromes. It integrates neuroimaging modalities (PET, SPECT, MRI) with pathology-based approaches (α-synuclein assays, skin biopsy) and clinical frameworks, offering a translational perspective that is highly relevant for diagnosis, stratification, and trial design. The breadth of coverage—from neurotransmitter dysfunction to co-pathologies and therapeutic implications—makes this report a valuable resource for clinicians and researchers. Paper addresses multiple biomarker domains: dopaminergic, noradrenergic, cholinergic, serotonergic systems, proteinopathies, neuroinflammation, and co-pathologies.

 

The report is structured into four thematic sections:

Section 1: Imaging neurotransmitter dysfunction (dopaminergic, noradrenergic, cholinergic, serotonergic).

Section 2: Molecular imaging of pathology (α-synuclein, tau, amyloid, neuroinflammation).

Section 3: Pathology-to-mechanism models (seed amplification assays, skin biopsy, co-pathology, brain-first vs body-first framework).

Section 4: Clinical translation and progression tracking (prodromal stages, resilience, connectomics, MRI biomarkers, management strategies).

The organization is logical and facilitates a progressive understanding from molecular insights to clinical applications.

Paper includes both imaging and pathology-based approaches, bridging molecular mechanisms with clinical applications. I believe that this paper synthesizes current knowledge on biomarkers in PD.

AA reply: We thank the reviewer for the general positive comment.

 

I have only one suggestion to create a table summarizing biomarkers in PD based on this article would enhance clarity and would have a practical utility. This would be extremely valuable, especially since the article discusses the technical aspects in great detail; such a summary would be incredibly useful for physicians/scientists less familiar with the techniques discussed.

AA reply: We thank the reviewer for the thoughtful comment. We have created a dedicated biomarker summary table as Supplementary Table 1 that synthesizes all the biomarkers discussed in the manuscript, grouped by domain (e.g., neurotransmitter dysfunction, imaging brain pathology, structural and network-based imaging, and in vivo pathology). For each biomarker, we provide: (i) the modality (e.g., PET, SPECT, MRI, fluid-based, electrophysiological); (ii) the relevant disease stage (prodromal, early, advanced); (iii) its main clinical and/or research application. Finally, keeping consistence to Figure 5, we provide color-coded maturity level, indicating whether the biomarker is clinically established (green), emerging with/without ongoing validation (orange), or still in the research/experimental phase (red). We believe this addition improves the overall accessibility and didactic value of the report and will serve as a practical reference for clinicians and scientists.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Dr. Cilia,

 even if such remark may not sound too professional, I would like to point out that the added Figures 3 an 5 and the supplemental material look terrific and are highly useful to the reader. Once published, I will use those Figures in my student lectures, as they condense top experts up to date view on the disease far beyond the SNpc degeneration. I am also impressed that you were able to provide those Figures so fast.

There is  a "Dmentia" typo in the Figure 3 legend.

Otherwise, a job excellently done.