Understanding Physical Exam Findings Associated With FND - Part 4

In the final episode of this series, Casey Kozak discusses functional sensory loss. 

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:

Welcome back to Neurology Minute. My name is Casey Kozak, and today we're finishing our discussion of functional neurological disorder and physical exam findings. We're going to now turn to functional sensory loss. But first, it's important to acknowledge that the subjective nature of sensory symptoms means that our physical exam tests will be less reliable than those used for functional weakness or movement disorders. Therefore, it's especially important that we as physicians listen carefully to the symptoms our patients are describing and remain aware of the potential for biases such as suggestion, when taking our histories. Nevertheless, there is certainly utility in physical exam tests as positive findings are present in many patients. We're going to discuss a few of these findings. The first is midline splitting, meaning that the patient's sensory loss has a clear edge at the midline of the body. For example, a patient may describe total sensory loss on the right side of their body, including their face, arm, and leg. 

And on testing, their sensory loss resolves in exactly the middle of their trunk. This is an unusual finding for sensory loss caused by central lesions, as the trunk is typically spared. The one exception to this rule, however, are thalamic lesions, which may be caused by stroke or mass effect, for example. While midline splitting is not a sensitive finding, it has a relatively high specificity if present. The second finding is splitting a vibration sense. This time, you will use your tuning fork to measure vibratory sensation across a bone that crosses midline, such as the frontal bone or the sternum. The sensation should be the same across the entire bone as vibration is perceived throughout bone conduction. Splitting a vibration, meaning there is loss of vibratory sensation on the numb side of the body is consistent with functional sensory loss because it defies its principle. Unlike midline splitting, however, splitting a vibration sense has been found to have a much lower specificity in testing.

Finally, sensory deficits may be precisely demarcated by anatomical borders, such as the shoulder or the groin, which is incongruent with peripheral nerve distributions. Beyond these examples, there are many more findings that can suggest FND in patients experiencing motor, sensory, or even visual, gait, or cognitive symptoms. Functional neurological disorder is a challenging disorder, though our understanding of it is improving. If you haven't yet, I highly encourage you to check out the seven-part Neurology Minute series on FND by Jon Stone and Gabriela Gilmour, focusing on recent advances in diagnosis and treatment. With that, thank you for joining us.