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Clinical Factors Underlying the Inter-individual Variability of the Resting Motor Threshold in Navigated Transcranial Magnetic Stimulation Motor Mapping

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Abstract

Correctly determining individual’s resting motor threshold (rMT) is crucial for accurate and reliable mapping by navigated transcranial magnetic stimulation (nTMS), which is especially true for preoperative motor mapping in brain tumor patients. However, systematic data analysis on clinical factors underlying inter-individual rMT variability in neurosurgical motor mapping is sparse. The present study examined 14 preselected clinical factors that may underlie inter-individual rMT variability by performing multiple regression analysis (backward, followed by forward model comparisons) on the nTMS motor mapping data of 100 brain tumor patients. Data were collected from preoperative motor mapping of abductor pollicis brevis (APB), abductor digiti minimi (ADM), and flexor carpi radialis (FCR) muscle representations among these patients. While edema and age at exam in the ADM model only jointly reduced the unexplained variance significantly, the other factors kept in the ADM model (gender, antiepileptic drug intake, and motor deficit) and each of the factors kept in the APB and FCR models independently significantly reduced the unexplained variance. Hence, several clinical parameters contribute to inter-individual rMT variability and should be taken into account during initial and follow-up motor mappings. Thus, the present study adds basic evidence on inter-individual rMT variability, whereby some of the parameters are specific to brain tumor patients.

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Abbreviations

II:

Astrocytoma WHO grade II

III:

Astrocytoma WHO grade III

IV:

Astrocytoma WHO grade IV

ADM:

Abductor digiti minimi muscle

AED:

Antiepileptic drug

APB:

Abductor pollicis brevis muscle

BCS:

Biceps brachii muscle

BMRC:

British Medical Research Council

D:

Deficit

DO:

Dominant

E:

Edema

EMG:

Electromyography

F:

Female

FCR:

Flexor carpi radialis muscle

FLAIR:

Fluid-attenuated inversion recovery

FR:

Frontal

ISI:

Inter-stimulus interval

L:

Levetiracetam

LH:

Left hemisphere

M:

Male

ME:

Metastasis

MEP:

Motor evoked potential

MFG:

Middle frontal gyrus

MRI:

Magnetic resonance imaging

NA:

No AED

ND:

No deficit

NDO:

Non-dominant

NE:

No edema

NK:

AED status not known

NR:

No recurrence

nTMS:

Navigated transcranial magnetic stimulation

PA:

Parietal

PoG:

Postcentral gyrus

PrG:

Precentral gyrus

R:

Recurrence

RH:

Right hemisphere

rMT:

Resting motor threshold

RO:

Rolandic

SA:

Specified AED

SFG:

Superior frontal gyrus

TE:

Temporal

TMS:

Transcranial magnetic stimulation

UA:

Unspecified AED

UDO:

Unknown dominancy

X:

Other entities

Y10:

Exam year 2010

Y11:

Exam year 2011

Y12:

Exam year 2012

Y13:

Exam year 2013

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Acknowledgements

NS gratefully acknowledges the support of the Graduate School’s Faculty Graduate Center of Medicine at our university.

Funding

The study was financed by Institutional Grants from the Department of Neurosurgery and the Section of Neuroradiology.

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    Authors and Affiliations

    1. Department of Neurosurgery, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675, Munich, Germany

      Nico Sollmann, Lucia Bulubas, Jamil Sabih, Florian Ringel, Bernhard Meyer & Sandro M. Krieg

    2. TUM-Neuroimaging Center, Klinikum rechts der Isar, Technische Universität München, Munich, Germany

      Nico Sollmann, Lucia Bulubas, Jamil Sabih, Claus Zimmer & Sandro M. Krieg

    3. Faculty of Linguistics, Philology & Phonetics, University of Oxford, Walton Street, Oxford, OX1 2HG, UK

      Noriko Tanigawa

    4. Section of Neuroradiology, Department of Radiology, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675, Munich, Germany

      Claus Zimmer

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    FR and SK are consultants for BrainLAB AG (Feldkirchen, Germany). SK is Consultant for Nexstim Oy (Helsinki, Finland). The authors declare that they have no conflict of interest regarding the present study.

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    Nico Sollmann and Noriko Tanigawa have contributed equally.

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    Sollmann, N., Tanigawa, N., Bulubas, L. et al. Clinical Factors Underlying the Inter-individual Variability of the Resting Motor Threshold in Navigated Transcranial Magnetic Stimulation Motor Mapping. Brain Topogr 30, 98–121 (2017). https://doi.org/10.1007/s10548-016-0536-9

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