McArdle’s sign refers to a rapidly reversible motor weakness brought about by head flexion in patients with multiple sclerosis (MS).

It may aid in MS diagnosis in some cases.

Using the test, it is found a 10% decrease in strength with flexion, which was 100% specific and 63% sensitive, for MS compared with other myelopathies.

They also observed an 8% decrease in strength with flexion for MS compared with healthy controls.

It is a specific and moderately sensitive test for diagnosis of MS and may supplement diagnosis in certain clinical situations.