Contributor: Travis Barlock, MD

Educational Pearls:

What is Hoover's sign used to identify?

This physical exam maneuver differentiates between organic vs. functional (previously known as psychogenic) leg weakness.
Organic causes include disease processes such as stroke, MS, spinal cord compression, guillain-barre, ALS, and sciatica, among others
In Functional Neurologic Disorder, the dysfunction is in brain signaling, and treatment relies on more of a psychiatric approach

How is Hoover's Sign performed?

Place your hand under the heel of the unaffected leg and ask the patient to attempt to lift the paralyzed leg.
If the paralysis is due to an organic cause, then you should feel the unaffected leg push down.
This is due to the crossed-extensor reflex mechanism, an unconscious motor control function mediated by the corticospinal tract.
If you don't feel the opposite heel push down, that is a positive Hoover's Sign.

How sensitive/specific is it?

An unblinded cohort study in patients with suspected stroke found a sensitivity of 63% and a specificity of 100%

Fun Fact

There's also a pulmonary Hoover's sign, named after the same doctor, Charles Franklin Hoover, which refers to paradoxical inward movement of the lower ribs during inspiration due to diaphragmatic flattening in COPD.

References

McWhirter L, Stone J, Sandercock P, Whiteley W. Hoover's sign for the diagnosis of functional weakness: a prospective unblinded cohort study in patients with suspected stroke. J Psychosom Res. 2011 Dec;71(6):384-6. doi: 10.1016/j.jpsychores.2011.09.003. Epub 2011 Oct 6. PMID: 22118379.
Stone J, Aybek S. Functional limb weakness and paralysis. Handb Clin Neurol. 2016;139:213-228. doi: 10.1016/B978-0-12-801772-2.00018-7. PMID: 27719840.

Summarized by Jeffrey Olson, MS3 | Edited by Jorge Chalit, OMS3