Several maneuvers can differentiate true neurologic motor weakness from poor effort (of whatever reason, be it psychological, or frank malingering).
1. “Break-Away” — When testing strength-against-resistance, true weakness gives way smoothly & continuously. Imagine a close arm-wrestling match, and the slow, gradual way the victor triumphs. In contrast, “weakness” that’s manifested in jerky spurts is not full effort.
2. Hoover’s Test for factitious leg weakness.
One way to perform is as shown in the picture, testing factitious weakness of Right hip extension.
For the more common “weakness” of hip flexion [“can’t lift the leg”], cradle the opposite heel in one hand as shown, while testing flexion against resistance. If you can’t feel downward pressure of the heel into your palm, there’s poor effort of the contralateral leg that’s supposedly trying to lift lifting up. In other words, if patient in picture complained of “Left leg weakness,” but didn’t push off with Right heel during the attempt, there was lack of effort.
3. Drift Without Pronation [for shoulder “weakness”] — Have the patient close their eyes and extend both arms out, palms up. Be sure the thumbs are pointed way out, well-supinated. Then observe for a minute. If an arm drifts down while the palms remain up, it’s by definition factitious. Pronation always occurs first, before the downward drift. Try it yourself: when you tire, first thing you do is pronate.
4. Factitious “Bell’s Palsy” — Have the patient squeeze both eyes shut, hard as they can. Gently try to open a lid. If it gives way easily, look at the eye. With true facial palsy, you see sclera, as the globe rolls upward (a protective reflex that accompanies squeezing the eyes shut, not involving the 7th cranial nerve). So if the pupil winds up staring right at you, it means the patient wasn’t truly trying hard.
True Bell’s Palsy