Abstract
Objective
To measure McArdle sign (rapidly reversible weakness induced by neck flexion) both
qualitatively and quantitatively and to evaluate its specificity and clinical utility
for diagnosis of multiple sclerosis (MS).
Patients and Methods
In this prospective study, McArdle sign was evaluated by a technician blinded to diagnosis
by measuring changes in finger extensor strength in successive trials of neck extension
and flexion, first clinically and then with a torque measurement device. We studied
25 healthy controls and 81 patients with finger extensor weakness. Patients were not
selected for having McArdle sign. Fifty-two patients had MS, 24 had other myelopathies,
and 5 had peripheral nerve lesions accounting for their weakness. The study was conducted
between February 1, 2016, and June 30, 2017.
Results
The median clinical McArdle sign and the 2 quantitative measures of neck flexion–induced
strength reduction were greater in patients with MS than in the other groups (P<.001). Baseline strength did not confound the difference. The area under the receiver
operating characteristic curve was 0.84 (95% CI, 0.75-0.93) comparing patients with
MS vs healthy controls and 0.84 (95% CI, 0.75-0.93) comparing MS vs patients with
other myelopathies. The 2 quantitative and 1 clinical measurement of McArdle sign
by the technician who performed the quantitative testing were correlated (r=.57 and r=.58; P<.001), and in turn, the technician's and unblinded referring physician's clinical
assessments were correlated (r=.58; P<.001). McArdle sign was evident in some patients who had minor disability and who
were in early phases of MS.
Conclusion
McArdle sign, when defined as greater than 10% neck flexion–induced reduction in strength,
is entirely specific and 65% sensitive for a diagnosis of MS when compared with other
conditions that mimic MS-associated myelopathy. It may facilitate diagnosis in certain
clinical situations.
Trial Registration
clinicaltrials.gov Identifier: NCT03122873.
Abbreviations and Acronyms:
EDSS (Expanded Disability Status Scale), HC (healthy controls), McS (McArdle sign), MRI (magnetic resonance imaging), MS (multiple sclerosis), OM (other myelopathy), PNL (peripheral nerve lesion), ROC (receiver operating characteristic curve)To read this article in full you will need to make a payment
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Article info
Publication history
Published online: July 11, 2019
Footnotes
For Limelight, see page 1391
Grant Support: This work was supported by a grant from the Center for Multiple Sclerosis and Autoimmune Neurology at Mayo Clinic and funds from the Materials and Structural Testing Resource Core of Mayo Clinic.
Potential Competing Interests: Dr Weinshenker is a member of adjudication boards and data safety monitoring committees for Alexion, Novartis Pharmaceuticals Corporation, and Viela Bio, is a consultant for BrainStorm Cell Therapeutics, Caladrius Biosciences, Chugai Pharmaceutical Co, Ltd, and Roivant Sciences Ltd, and has received travel expenses from Alexion. The other authors report no competing interests.
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© 2019 Mayo Foundation for Medical Education and Research
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- In the Limelight: August 2019Mayo Clinic ProceedingsVol. 94Issue 8
