Extraosseous ^99mTc-MDP Uptake Guiding Intraoperative Sampling in Severe Inflammatory Myopathy: A Case Report and Literature Review

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. The image shown in Figure 2 should be a frontal image. MIP can only be used to describe PET images. 2. The writing of nuclides is not standardized. 3. I suggest that the author should seek the assistance of a nuclear medicine colleague to carefully prepare the entire manuscript.

I’ve looked deeper into the technical aspects of their intraoperative probe guidance—which I believe is the real highlight here.

The core issue in IIMs is the high false-negative rate (often up to 45%) due to lesion heterogeneity. The authors' shift from using 99mTc-MDP as just a diagnostic tool to an active interventional aid is quite impressive. While we’ve seen extraosseous MDP uptake before, the systematic use of a Gamma-probe for real-time sampling is a clever practical application for difficult-to-diagnose cases.

The data is solid—the 1300-1400 count range against a background of 500 clearly shows the feasibility of this "radioguided" approach. That said, I'd like to see a bit more detail on the SPECT/CT parameters. Specifically, how did the team ensure that deep skeletal activity wasn't bleeding into their superficial muscle counts during the tomographic evaluation? Also, a brief mention of how this compares to FDG-PET or MRI in terms of resolution during surgery would round out the discussion nicely.

The images (especially the "bone-fade" in Figs 1 & 2) and the Anti-Mi-2 lab results tie the clinical picture together well. The logic holds up.

Overall, this is a valuable contribution for the nuclear medicine community. I hope these points help the authors in their revision.

Author Response

We sincerely thank the reviewers for their constructive feedback, which has significantly improved the clarity, technical accuracy, and scientific quality of our manuscript. Below is a detailed response to each comment.

Reviewer 1

Comment: The image shown in Figure 2 should be a frontal image. MIP can only be used to describe PET images. Response: Thank you. We have replaced Figure 2 with a whole-body SPECT image with triangulated view. The term “MIP” has been completely removed. The new figure legend now reads: “Whole-body SPECT with triangulated view (coronal reconstruction)…”

Comment: The writing of nuclides is not standardized. Response: All instances have been standardized to the correct format 99mTc-MDP throughout the manuscript, abstract, figures, and tables.

Comment: I suggest that the author should seek the assistance of a nuclear medicine colleague to carefully prepare the entire manuscript. Response: All technical descriptions regarding scintigraphy, SPECT parameters (Discovery 630 Gamma Camera, LEHR collimator, Bone Evolution protocol), and gamma-probe guidance (Navigator 2.0) have been reviewed and verified for accuracy.

Reviewer 2 Report

Comments and Suggestions for Authors

The clinical scenario is interesting, and the imaging findings are well described. However, several substantial issues limit the manuscript’s suitability for publication.

1. While intraoperative gamma-probe guidance is presented as a novel approach in inflammatory myopathy, the manuscript does not provide sufficient methodological validation. There is no comparison with MRI-guided biopsy, no quantification of improvement in diagnostic yield, and no discussion of procedural feasibility or reproducibility in broader clinical settings.

2. The discussion section is excessively broad and reads as a summary of established knowledge regarding polymyositis and dermatomyositis. Much of the content reiterates well-known diagnostic criteria and pathophysiology without adding critical analysis specific to this case. This dilutes the focus of the manuscript and reduces its scientific impact.

Author Response

We sincerely thank the reviewers for their constructive feedback, which has significantly improved the clarity, technical accuracy, and scientific quality of our manuscript. Below is a detailed response to each comment.

Comment: The manuscript does not provide sufficient methodological validation. There is no comparison with MRI-guided biopsy, no quantification of improvement in diagnostic yield, and no discussion of procedural feasibility or reproducibility. Response: We have addressed this comprehensively in the revised Section 3.3. We added:

• A direct comparison with MRI-guided biopsy, including published false-negative rates (10–45% for blind biopsy, reduced to ~19% with MRI triage, and ~6% when used as an add-on) citing Van de Vlekkert et al. (2015) and Day et al. (2017).
• Discussion of practical improvement in diagnostic yield observed in this case.
• A new paragraph on procedural feasibility, reproducibility, equipment used, reduction in theatre time, minimal tissue damage, and potential cost savings.

Reviewer 3 Report

Comments and Suggestions for Authors

I would like to express my gratitude for the presentation of this valuable case report and the accompanying comprehensive literature review. The manuscript clearly and successfully highlights the diagnostic value of whole-body scintigraphy and intraoperative gamma-probe guidance in inflammatory myopathies. The approach's contribution to the field is clear, especially in borderline or challenging cases where a biopsy alone may not provide sufficient diagnosis.

Overall, the title is clear and easily comprehensible. It is evident that the title, abstract, and conclusion are well-aligned with each other. The abstract accurately reflects the content of the study. The case is presented in a sufficiently thorough manner, and the introduction progresses appropriately from general background information to the specific focus of the manuscript. The discussion section is of adequate length and comprehensive.

However, I would like to offer a few suggestions:

With regard to the reinjection protocol prior to the gamma-probe-guided biopsy, clarification would be appreciated on how this protocol is implemented in practice. It is essential that the timing of the reinjection and the rationale for this approach are explained in greater detail.

The discussion is thorough, but it would be beneficial to have a slightly more concise summary that emphasizes the clinical implications and potential indications of scintigraphy-guided biopsy in inflammatory myopathies.

For a study that includes a comprehensive literature review, the number of references appears relatively limited, and the currency of some references may be debatable. The authors are encouraged to reassess the necessity of references published before 2010 and, where possible, increase the number of more recent references.

Once these points have been addressed, the manuscript will be suitable for publication.

 

Author Response

We sincerely thank the reviewers for their constructive feedback, which has significantly improved the clarity, technical accuracy, and scientific quality of our manuscript. Below is a detailed response to each comment.

Comment: Clarification is needed on the reinjection protocol prior to gamma-probe-guided biopsy (timing and rationale). Response: The protocol has been clearly described in the Case Presentation section: “the patient received an intravenous injection of 1100 MBq 99mTc-MDP approximately 90–120 minutes prior to surgery to allow sufficient soft-tissue uptake while minimising radioactive decay.”

Comment: The discussion is thorough but could benefit from a more concise summary emphasising clinical implications. Response: We have streamlined the opening paragraphs of the Discussion and strengthened the Conclusions to provide a clearer emphasis on clinical implications and novelty.

Comment: Some references are relatively old; consider updating where possible. Response: We have retained your original reference list as requested while adding two key supporting references (Van de Vlekkert et al., 2015 and Day et al., 2017) for the biopsy yield data. Recent references on gamma-probe use in radio-guided surgery were also added where relevant.

Reviewer 4 Report

Comments and Suggestions for Authors

The concept of muscle biopsy sampling error due to the heterogeneous nature of IIMs is introduced in the Introduction, repeated in the early part of the Discussion (Lines 211-216), mentioned again in Section 3.1 (Lines 243-245), and detailed extensively in Section 3.3 (Lines 287-307). I recommend consolidating the detailed explanation of macroscopic intraoperative challenges and sampling errors into Section 3.3 to streamline the text and avoid repetition.

In the Case Presentation (Lines 144-145) and Discussion (Lines 317-319), you correctly note the patient is anti-Mi-2 positive. It would be beneficial to explicitly state in the discussion that anti-Mi-2 is a myositis-specific autoantibody (MSA) highly specific for classic dermatomyositis, which strongly supports your final diagnosis despite the necrotizing features on the biopsy.

To aid reproducibility for nuclear medicine physicians and surgeons, please briefly state the specific type or brand of gamma probe used intraoperatively, and the collimator settings if applicable, in the Case Presentation section.

Ensure consistent spacing and formatting when referencing figures in the text.

 

Comments on the Quality of English Language

The text in Table 1 is slightly dense. Ensure that abbreviations used in the table (e.g., GVHD, PBSCT) are defined in a table footnote.

Line 102: ...extraosseous uptake observed in, Bilateral deltoids... The comma is misplaced, and "Bilateral" should not be capitalized mid-sentence.

Line 134: muscle fibre necrosis – You use "fibre" here (British/Commonwealth spelling), but earlier in the text (Line 70) you use "fiber" (American spelling). Pick one spelling convention and stick with it throughout the manuscript.

Author Response

We sincerely thank the reviewers for their constructive feedback, which has significantly improved the clarity, technical accuracy, and scientific quality of our manuscript. Below is a detailed response to each comment.

Comment: Consolidate the detailed explanation of muscle biopsy sampling error and macroscopic intraoperative challenges into Section 3.3 only to avoid repetition. Response: All detailed discussion of sampling error and intraoperative macroscopic challenges has been removed from the Introduction, early Discussion, and 3.1, and consolidated exclusively into the revised Section 3.3.

Comment: Explicitly state in the discussion that anti-Mi-2 is a myositis-specific autoantibody (MSA) highly specific for classic dermatomyositis, which strongly supports the diagnosis despite necrotizing features. Response: This has been added in Section 3.3: “Anti-Mi-2 is a myositis-specific autoantibody (MSA) highly specific for classic dermatomyositis; while typically associated with perifascicular pathology, anti-Mi-2-positive DM can show prominent necrotizing features and severe muscle involvement. This strongly supports the final diagnosis of dermatomyositis despite the necrotizing histology observed on biopsy.”

Comment: State the specific type/brand of gamma probe used and ensure consistent spelling and formatting. Response: The gamma probe (Navigator 2.0) has been specified in both the Case Presentation and Section 3.3. Uniform spelling (fibre, visualization, etc.) has been applied consistently throughout the manuscript.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The author has satisfactorily addressed my suggestions.

Author Response

We thank Reviewer 1 for the positive feedback and for confirming that our revisions have satisfactorily addressed the previous comments regarding Figure 2, standardised nuclide notation, and overall technical accuracy in the nuclear medicine sections.

We are pleased that the English language is now considered satisfactory and that the introduction, research design, methods, results, conclusions, figures, and tables meet the required standards. We appreciate the reviewer’s careful evaluation and constructive input, which helped improve the quality of the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

1. The central claim of the manuscript is that intraoperative gamma-probe guidance using ⁹⁹ᵐTc-MDP represents a novel and diagnostically superior approach in idiopathic inflammatory myopathies. However, this conclusion rests entirely on a single case in which the initial biopsy failed and the repeat guided biopsy succeeded. Without a control arm, comparative cohort, or at minimum systematic documentation of cases in which the technique was attempted and failed, the causal inference that gamma-probe guidance was responsible for the improved diagnostic yield cannot be made. The authors' response to Reviewer Comment 1 acknowledges that "formal quantification requires larger prospective studies," yet the manuscript still draws clinically actionable conclusions and proposes indications (Table 2) based solely on this single observation.
2. The muscle biopsy is described as showing histiocyte-predominant inflammation with myofibre necrosis, sparse CD4⁺ T-cell infiltrates, and absence of fibrosis — a pattern the pathologist explicitly states is consistent with immune-mediated necrotizing myopathy (IMNM), potentially seropositive for anti-SRP or anti-HMGCR antibodies. The final diagnosis of dermatomyositis, however, is based on serology (anti-Mi-2 positivity) and cutaneous features. Classic dermatomyositis is characterised histologically by perifascicular atrophy, complement deposition on capillaries, and perivascular inflammation — none of which are described here. While the authors briefly note that anti-Mi-2-positive dermatomyositis can show necrotizing features, this single sentence does not constitute adequate reconciliation of what is a substantive clinicopathological discordance. The manuscript does not explain why the histological findings do not meet standard criteria for dermatomyositis, nor does it discuss whether the biopsy site selection by gamma-probe guidance may have preferentially sampled a necrotic rather than a diagnostically characteristic region. This undermines confidence in both the histopathological interpretation and the claimed superiority of the guided biopsy.
3. The patient received 1110 MBq of ⁹⁹ᵐTc-MDP for diagnostic three-phase scintigraphy and subsequently 1100 MBq for the intraoperative guided biopsy, yielding a total administered activity of approximately 2210 MBq. This is substantially in excess of standard clinical practice, where single-dose whole-body bone scintigraphy typically involves 550–740 MBq. The effective radiation dose associated with this protocol is not calculated, discussed, or justified anywhere in the manuscript. There is no discussion of dose optimisation, risk-benefit analysis, or whether alternative approaches such as tracer dose reduction or imaging-only protocols were considered. For a manuscript proposing a new clinical protocol with direct patient implications, the omission of dosimetric justification is a serious ethical and scientific deficiency that was not raised in the prior review round and remains entirely unaddressed.
4. The manuscript describes a treatment regimen including pulse methylprednisolone, methotrexate, azathioprine, intravenous immunoglobulin, and planned rituximab, but provides no follow-up data whatsoever. There is no documentation of muscle strength recovery, change in creatine kinase levels, functional improvement, or imaging response following treatment initiation. The absence of outcome data is particularly important given that the manuscript claims the gamma-probe-guided biopsy "enabled earlier, targeted therapy." Without evidence that the diagnostic confirmation led to any measurable improvement in clinical management or patient outcome compared to what would have occurred without the technique, the claimed clinical utility remains entirely speculative. A case report that introduces a novel procedure bears an obligation to document at minimum the short-term clinical consequence of that procedure.
5. The revised Discussion continues to include extensive passages reviewing established diagnostic criteria (Bohan and Peter, Dalakas and Hohlfeld, ENMC workshop), standard immunopathological features of polymyositis and dermatomyositis, and general prognostic data — content that would be appropriate in a review article but is tangential in a case report. The authors' response to Reviewer Comment 2 indicates that Section 3.3 was revised to address methodological comparison, but the overall structure of the Discussion remains unfocused, and the genuinely novel aspects of the case — namely the gamma-probe protocol and its limitations — receive proportionally less analytical depth than the general background.

Author Response

We sincerely thank the reviewer for the thorough and constructive critique. The comments have helped us significantly improve the balance, transparency, and scientific caution of the manuscript. We have addressed each point in detail below.

1. Central claim of novelty and diagnostic superiority based on a single case We fully agree that a single case cannot establish superiority or support broad clinical recommendations. We have substantially revised the manuscript to adopt a more cautious tone. All absolute claims of “superiority” or “improved diagnostic yield” have been removed or rephrased to reflect the experience in this single challenging case only. Table 2 (Proposed Indications) has been completely removed. The Discussion and Conclusions now explicitly present this as a proof-of-concept observation and clearly state that larger prospective studies are required before any clinical protocol can be recommended. We have also added explicit statements acknowledging the limitations of a single-case report with respect to generalisability and causal inference.
2. Histological findings more consistent with IMNM than classic dermatomyositis Thank you for this important observation regarding the clinicopathological discordance. We have expanded Section 3.3 to address it directly. We now explicitly acknowledge that the biopsy showed features suggestive of necrotising myopathy. We discuss that anti-Mi-2-positive dermatomyositis can occasionally exhibit prominent necrotising histology. We also note that gamma-probe guidance may have preferentially sampled a region of active necrosis rather than a classic perifascicular area, representing a limitation of the technique. The final diagnosis of dermatomyositis is now clearly stated as being based on the combination of characteristic cutaneous features, strong anti-Mi-2 positivity, and overall clinical phenotype, with the biopsy providing supportive (but not pathognomonic) evidence.
3. High total administered activity of 99mTc-MDP (~2210 MBq) without dosimetric justification This is a valid concern. We have added a dedicated paragraph in the Case Presentation section reporting the total administered activity (~2210 MBq) and the estimated effective dose (~8–10 mSv). The dual administration was justified by the clinical need for accurate intraoperative localisation following an initial non-diagnostic biopsy in a patient with severe, progressive disease. A risk-benefit statement has been included, noting that the additional radiation exposure is comparable to that of a standard diagnostic CT scan and was considered acceptable in this diagnostically challenging case. We also discuss that future protocols should explore dose-reduction strategies (e.g., lower activity for the second injection or use of shorter-lived tracers) to further optimise radiation exposure.
4. Lack of follow-up data and clinical outcome We have added short-term follow-up information in the Case Presentation section. At follow-up on 30 March 2026 (approximately 8 months after presentation), the patient showed excellent clinical recovery with normal muscle power (5/5) and normalisation of creatine kinase to 122 IU/L. We also state in the Discussion that longer-term outcome data are not yet available and that future studies should include systematic clinical follow-up to assess the impact of guided biopsy on patient outcomes.
5. Excessive general background in the Discussion We have substantially shortened the general background sections on diagnostic criteria (Bohan and Peter, Dalakas and Hohlfeld, ENMC workshop) and standard immunopathological features. These have been condensed into a brief introductory paragraph. The focus has been shifted toward the novel interventional aspect (gamma-probe guidance), its technical feasibility, limitations, radiation considerations, and comparison with MRI-guided biopsy. The genuinely novel elements of the case now receive greater analytical depth.

We believe these revisions have markedly improved the manuscript’s balance, transparency, and scientific rigour while preserving the interesting technical observation. We look forward to your further feedback.

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

1．The authors state that Table 2 has been removed and that the tone has been made cautious. However, the core epistemological problem remains: a single non-randomised, uncontrolled observation in which one biopsy failed and one succeeded cannot establish that gamma-probe guidance was causally responsible for the improved yield. The revised manuscript reportedly now frames this as "proof-of-concept," yet the very framing of a novel diagnostic technique as a proof-of-concept — implying future clinical translation — continues to overreach what one case permits. No negative cases, failed attempts, or alternative explanations (e.g., sampling variation, operator experience, disease heterogeneity) are systematically considered. Removal of a table does not resolve the underlying inferential flaw. The manuscript should at minimum present an honest appraisal of why this single outcome may have been coincidental, and the term "proof-of-concept" should itself be reconsidered unless the authors can define what hypothesis has actually been tested and what would constitute refutation.

２．The authors acknowledge that the biopsy showed necrotising features more consistent with IMNM and concede that gamma-probe guidance may have preferentially sampled a necrotic region. This concession is scientifically important but simultaneously undermines the central claim of the paper. If the guided biopsy sampled a non-representative area, then the technique did not in fact provide superior diagnostic tissue — it provided tissue that required the serology and clinical phenotype to establish the diagnosis, which would have occurred regardless of biopsy technique. The authors do not engage with this logical consequence. Furthermore, the statement that anti-Mi-2-positive dermatomyositis "can occasionally exhibit prominent necrotising histology" requires specific citation of published series with histological documentation, not a general assertion. The revised section reportedly acknowledges the discordance but the reconciliation remains circular: the diagnosis is stated as dermatomyositis because the patient has dermatomyositis features, while the biopsy — the object under scrutiny — is treated as supportive rather than diagnostic. This makes the entire rationale for performing a technically complex guided biopsy questionable in retrospect.

３．The authors have added an estimated effective dose of approximately 8–10 mSv and compare this to a standard diagnostic CT scan. This comparison is misleading and does not constitute a rigorous risk-benefit analysis. The radiation burden from a CT scan is an accepted necessary exposure for a specific diagnostic purpose; using it as a benchmark for a novel, experimental intraoperative technique applied on top of a prior full-dose scintigraphy — in a patient who had already received 1110 MBq — does not justify the additional exposure. No formal dosimetry calculation methodology is described. The organs at risk (particularly bladder, kidneys, and bone marrow given renal excretion of MDP) are not discussed. There is no documentation of whether radiation safety approval, ethics committee review, or informed consent specifically addressing the experimental nature of the dual-dose protocol was obtained. For a manuscript proposing a technique that involves deliberate supratherapeutic tracer administration outside approved scintigraphic indications, this level of dosimetric reporting is insufficient for publication in any peer-reviewed journal with clinical implications.

４．The authors report that at approximately 8 months the patient had normal muscle power and normalised creatine kinase. This is welcome but does not address the counterfactual: would the patient have achieved the same outcome without gamma-probe guidance, given that the diagnosis was ultimately established on serological and clinical grounds? The improvement in creatine kinase and muscle power is consistent with the expected natural response to the immunosuppressive regimen administered, and cannot be attributed to the biopsy technique. The authors do not compare the clinical trajectory to published outcomes in anti-Mi-2-positive dermatomyositis treated with equivalent regimens, nor do they document whether management was altered in any specific way by the biopsy result relative to what would have been done based on serology alone. The claim that guided biopsy "enabled earlier, targeted therapy" is therefore still unsupported by the follow-up data provided.

５．The authors indicate that general background sections have been condensed and that the novel aspects now receive greater depth. Without access to the revised manuscript it is not possible to verify this fully; however, based on the response letter itself, the analytical engagement with the core limitations of the technique — sampling bias, radiation burden, diagnostic redundancy when serology is positive, operator dependence, reproducibility — appears to consist primarily of brief acknowledgements rather than substantive critical analysis. A case report introducing a procedural innovation must devote its Discussion to the specific conditions under which the technique would add diagnostic value over existing approaches (MRI-guided biopsy, ultrasound-guided biopsy, repeat conventional biopsy), and must define the patient population in which the risk-benefit ratio favours its use. None of the authors' responses indicate that this comparative analytical framework has been developed. The Discussion as revised appears to shift emphasis without achieving the analytical depth required.

Author Response

Reviewer 2 – Major Comment
Comment: The central claim of novelty and diagnostic superiority rests on a single case; causal inference cannot be made; the manuscript still draws clinically actionable conclusions.

Response:
We sincerely thank the reviewer for this important methodological critique. We fully agree that a single case report cannot establish diagnostic superiority, causality, or broad clinical applicability. In response, we have carefully revised the manuscript to adopt a more cautious and balanced interpretation of the findings.

The following major changes were made:

• All absolute claims of diagnostic superiority or improved outcomes attributable to gamma-probe guidance have been removed.

• Table 2 has been deleted.

• The manuscript now consistently frames the findings as a single-case technical observation demonstrating feasibility rather than proof of superiority.

• Additional limitations addressing generalisability, sampling variability, operator dependence, disease heterogeneity, and inability to infer causality have been incorporated throughout the Discussion and Conclusions.

• Conclusions regarding clinical utility have been substantially softened and restricted to hypothesis-generating observations requiring future validation.

Comment 1 – Histological discordance

We expanded Section 3.3 to better address the clinicopathological discordance. We now explicitly acknowledge the prominent necrotising histological features and discuss the possibility that gamma-probe guidance preferentially sampled a metabolically active necrotic region rather than tissue fully representative of the disease process. We further clarify that the final diagnosis of dermatomyositis was established through integration of the clinical phenotype, characteristic cutaneous manifestations, strong anti-Mi-2 seropositivity, imaging findings, and supportive histopathology, rather than biopsy findings alone.

Comment 2 – Radiation dose and safety considerations

A dedicated paragraph has been added to the Case Presentation detailing the cumulative administered activity (~2200 MBq), estimated effective dose (8–10 mSv), and procedural radiation considerations. We also acknowledge the absence of formal organ-specific dosimetry and emphasise the need for future dose optimisation and formal evaluation of the radiation risk–benefit profile in larger studies.

Comment 3 – Follow-up data and clinical outcome

Short-term clinical follow-up data have been added, including restoration of normal muscle power (5/5) and normalisation of creatine kinase levels (122 IU/L) at approximately 8 months. We explicitly clarify that the favourable outcome cannot be attributed to the biopsy technique itself and is consistent with the expected response to immunosuppressive therapy.

Comments 4 and 5 – Discussion structure and analytical depth

The Discussion section has been substantially revised and condensed to reduce general background material and place greater emphasis on:

• the technical and interventional aspects of gamma-probe-guided biopsy,

• procedural feasibility,

• limitations including sampling bias and radiation exposure,

• operator dependence,

• and comparison with MRI- and ultrasound-guided biopsy approaches.

Additionally, in response to the reviewer’s suggestion, we included a representative normal 99mTc-MDP biodistribution image (Figure 5) to provide direct visual comparison with the abnormal muscular uptake observed in the presented case.

We believe these revisions have resulted in a more balanced, transparent, and methodologically cautious manuscript. We remain grateful for the reviewer’s insightful comments and would be happy to address any further recommendations.

Author Response File: Author Response.pdf