False Positive Hoover's Sign in Apraxia: A Case of Corticobasal Syndrome
FND Nope
Moderator
In a 2020 clinical report published in Movement Disorders Clinical Practice, neurologists Tommaso Ercoli and Jon Stone described a patient with positive Hoover's and hip abductor signs, two examination findings commonly associated with functional neurological disorder (FND). The patient was instead diagnosed with corticobasal syndrome, and the authors identified apraxia as an alternative explanation for the positive findings. Their report, titled False Positive Hoover's Sign in Apraxia, documents an important limitation in the diagnostic interpretation of these signs.
The Clinical Case
The patient was a 90-year-old woman with a five-year history of progressive difficulty moving her left arm and leg. Her daughter contacted neurologist Jon Stone because she wondered whether her mother's condition might be FND, particularly after noticing that some movements improved when her mother was distracted.
Neurological examination revealed marked left-sided rigidity, dystonia and severe apraxia, with probable limb-kinetic and ideomotor components. Apraxia is a disorder affecting the ability to plan or execute learned movements despite having the basic motor capacity to perform them. A person may struggle to carry out a movement on command while performing a similar movement more successfully in a familiar or automatic context.
Both Hoover's sign and the hip abductor sign were clearly positive. Brain MRI demonstrated posterior cortical atrophy, while a DaTscan was normal. Despite the normal DaTscan, the clinicians diagnosed corticobasal syndrome (CBS), a progressive neurological syndrome associated with combinations of movement abnormalities and higher-order motor dysfunction. The precise underlying pathology remained uncertain.
The authors included supplementary clinical video footage documenting the examination findings, including the positive Hoover's and hip abductor signs.
Why Were the Signs Positive?
Hoover's sign tests for a discrepancy between voluntary and automatic movement. A patient who appears unable to extend one hip voluntarily may nevertheless generate normal extension force when flexing the opposite hip against resistance. The hip abductor sign examines a related discrepancy, in which movement of the apparently weak leg emerges during resisted movement of the opposite leg.
These findings are commonly interpreted as evidence supporting functional weakness. However, the authors explain that apraxia, particularly ideomotor apraxia, can produce a similar dissociation. The difficulty lies in executing a requested movement rather than necessarily lacking the underlying capacity to produce it. In this patient, the discrepancy was therefore compatible with her neurological syndrome rather than establishing a functional cause.
The authors explicitly concluded that apraxia provided an alternative explanation for the positive Hoover's sign, making the finding nondiagnostic in this case. This distinction is important: the examination demonstrated a genuine discrepancy in motor performance, but the discrepancy did not uniquely identify its cause.
The Diagnostic Problem
The first concern is the relationship between an observed sign and the mechanism attributed to it. Hoover's sign demonstrates a difference between voluntary and automatic motor performance. It does not directly measure the underlying cause of that difference. When apraxia produces the same finding, interpreting the sign as evidence of FND without adequately considering alternative explanations risks confusing a clinical observation with a diagnosis.
The second concern is that two positive signs do not necessarily provide two independent pieces of diagnostic evidence. In this case, both Hoover's sign and the hip abductor sign were positive, yet the authors identified apraxia as an explanation for the findings. Because both tests depend on discrepancies between voluntary and automatic movement, they may share the same source of diagnostic error. Their agreement does not automatically establish that the proposed interpretation is correct.
A third concern involves the interpretation of normal investigations. The patient's DaTscan was normal, but the authors recognised that an abnormal DaTscan is not a mandatory feature of corticobasal syndrome. The diagnosis was therefore based on the broader clinical presentation, including the progressive history, rigidity, dystonia, apraxia and imaging findings. A normal investigation did not erase the neurological abnormalities observed during examination.
What Does This Mean for Diagnostic Specificity?
The report raises a question about how the specificity of Hoover's sign should be understood. A test may demonstrate high specificity in a particular validation population while producing false positives in neurological conditions that were absent or poorly represented in that population. A specificity estimate cannot automatically be generalised to every disorder capable of affecting voluntary motor control.
This is particularly relevant to apraxia because the overlap is not merely superficial. The authors identify voluntary–automatic dissociation as a recognised feature of apraxia, meaning that the neurological disorder can affect the very relationship that Hoover's sign examines. The problem is therefore not simply that two conditions look similar. It is that the proposed diagnostic distinction can break down when another disorder produces the same examination phenomenon.
The authors also identify other neurological presentations that can create comparable diagnostic pitfalls, including differences between emotional and voluntary facial movement in opercular syndrome, improvement during backward walking or running in dystonia, and suppressible movements in Tourette's syndrome. These examples illustrate why apparent inconsistency or context-dependent improvement cannot be interpreted independently of the condition producing it.
Why This Case Matters
One notable aspect of this report is that Jon Stone, a prominent contributor to the literature on positive diagnostic signs in FND, is one of its authors. The limitation is therefore acknowledged within the same clinical literature that describes these signs as useful diagnostic findings. The authors do not present the case as a documented FND misdiagnosis. Rather, they demonstrate how such a misinterpretation could occur if the examination signs were considered without sufficient attention to the wider neurological presentation.
As a single case report, the publication cannot establish how frequently apraxia produces false-positive Hoover's signs. It does, however, document that the phenomenon can occur and identifies a plausible neurological explanation. That leaves an important question for larger validation studies: how reliably can Hoover's sign distinguish functional weakness from disorders involving apraxia and other disturbances of voluntary motor control?
The broader diagnostic lesson is that a positive sign must not be allowed to override contradictory clinical evidence. In this case, progressive neurological abnormalities, apraxia and structural imaging findings were essential to understanding why the examination behaved as it did. Had the positive signs been treated as sufficient evidence of FND, the same findings could have supported a substantially different diagnostic conclusion.
References
- Ercoli T, Stone J. False Positive Hoover's Sign in Apraxia. Movement Disorders Clinical Practice. 2020;7(5):567–568. doi:10.1002/mdc3.12970.
- Leiguarda RC, Marsden CD. Limb apraxias: higher-order disorders of sensorimotor integration. Brain. 2000;123(5):860–879.
- Cilia R, Rossi C, Frosini D, et al. Dopamine transporter SPECT imaging in corticobasal syndrome. PLoS ONE. 2011;6(5):e18301.
- Stone J, Reuber M, Carson A. Functional symptoms in neurology: mimics and chameleons. Practical Neurology. 2013;13(2):104–113.
