Understanding Physical Exam Findings Associated With FND - Part 3

In part three of this four-part series, Casey Kozak discusses the hip abductor sign as an option for assessing weakness in the lower extremities. 

Show citation:

Sonoo M. Abductor sign: a reliable new sign to detect unilateral non-organic paresis of the lower limb. J Neurol Neurosurg Psychiatry. 2004;75(1):121-125. 

Show transcript:

Casey Kozak:

Hello, this is Casey Kozak with Neurology Minute, and today we're returning to physical exam tests for functional neurological disorder. This episode will piggyback off our last focusing on Hoover's sign, now focusing on other signs of functional weakness. Besides Hoover's sign, another option for assessing lower extremity weakness is the hip abductor sign. Remember that AB-duction means to move away from midline. To perform this test, the patient will be laying on their back. You will then place your hands on the outside of both of their legs. First, you will test the weak leg by asking the patient to push their weak leg outwards in AB-duction against the resistance of your hand. The weak leg will give way easily. Next, you will test the non-affected leg by asking the patient again to push outwards against the resistance of your hand. In a patient with functional weakness, the weak leg may exhibit spontaneous recovery of strength and push outwards against your resting hand while the patient is trying to push their unaffected leg out.

This is an automatic effort by the body to remain midline by engaging the opposite leg, and just like with Hoover's sign, this is based on the principle that the contralateral limb will produce an opposite movement pattern. However, in organic neurological weakness from neurodegeneration, stroke, or peripheral nerve damage, this isn't possible. Therefore, the hip abductor sign is positive if AB-duction of the unaffected leg against resistance causes improvement in the weaker leg's abductor strength. If you're a visual learner like me, don't worry. There's a great diagram for the hip abductor test in a paper by Masahiro Sonoo that we have linked to this episode.

What if a patient has upper extremity weakness? In this case, you can test for drift without pronation. Ask the patient to hold their arms up as of holding a large tray. Then, ask the patient to close their eyes and shake their head no to add distraction to the test and remove visual sensory input. Watch what their arms do. In normal neurological screening examinations, we test for pronator drift, in which the upper motor neuron damage causes a weak arm to fall while the hand pronates or turns inwards. However, in functional arm weakness, you may find that the patient exhibits dramatic drooping of the affected arm without pronation. Keep in mind, however, that this test is not entirely specific, and a musculoskeletal injury to the shoulder, even a remote one, may cause drift alone. If you notice this, it's helpful to inquire about past shoulder injuries. Finally, in any affected body part, you can test for give-way weakness, in which there is a sudden loss of resistance after initial good strength, like a switch was turned off. This abrupt collapse is inconsistent with muscle weakness originating in the musculoskeletal system or a central lesion, and may support a diagnosis with FND.

All right, this gives us plenty to practice with, so let's break again. Join us for the last episode of this series in which we'll discuss functional sensory loss. Until then, happy studying.