FND: Weakness Differential Clinical case Organic Clues Rule-In Signs Diagnostic Overshadowing Clinical Reasoning Unconfirmed Diagnosis

When Hoover's Sign Suggested Conversion Disorder, but Lyme Disease Entered the Picture

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A positive Hoover's sign, fluctuating weakness, anxiety and recent stressful life events. These were among the findings that led clinicians to seriously consider conversion disorder in a 62-year-old woman experiencing progressive neurological symptoms. But as her condition deteriorated and further investigations were performed, the evidence began pointing in a very different direction: peripheral nerve dysfunction, possible Guillain-Barré syndrome and ultimately suspected Lyme neuroborreliosis.

Published in Case Reports in Neurology in 2019, the case by Teodoro, Oliveira and Afonso illustrates what can happen when an unusual neurological presentation contains features commonly associated with functional neurological symptoms, alongside evidence of an underlying neurological disease. Particularly noteworthy is the reported positive Hoover's sign, a clinical examination finding frequently used to support a diagnosis of functional limb weakness.


From Weakness to Suspected Conversion Disorder

The patient, a 62-year-old woman visiting Portugal from England, initially attended hospital after developing weakness in her left hand and both legs. She had fallen twice, sustaining head trauma, and reported recent stressful life events. Routine blood tests and a head CT scan revealed no acute abnormalities, and she was discharged. She returned the following day with worsening weakness, substantial difficulty walking and urinary incontinence, prompting referral to a neurology department.

Neurological examination revealed weakness affecting all four limbs, reduced reflexes, altered sensation and an extensor plantar response on the left. These findings already raised the possibility of an underlying neurological disorder. However, clinicians also observed fluctuations and apparent inconsistencies in her weakness, which seemed to vary with her emotional state and degree of cooperation during examination. An early assessment additionally documented a positive Hoover's sign.

The combination of these observations, her anxiety and her account of recent stress led clinicians to consider a functional explanation. She was prescribed sertraline and pregabalin while investigations continued. MRI examinations identified cervical spinal canal narrowing and a thoracic disc herniation, but a neurosurgical assessment concluded that these findings did not adequately explain her symptoms.

What makes this case particularly important is that the suspicion of conversion disorder was not based simply on normal investigations or the absence of an obvious diagnosis. The clinicians reported features they interpreted as potentially positive evidence of functional neurological symptoms, including Hoover's sign and inconsistent weakness. Yet the same patient also exhibited objective neurological abnormalities that required further explanation.


The Investigations Changed the Picture

By the fifth day of admission, the patient's weakness had deteriorated substantially and her tendon reflexes were absent. A lumbar puncture revealed elevated cerebrospinal fluid protein, while electromyography identified a subacute motor axonal neuropathy. These findings suggested a possible acute motor axonal variant of Guillain-Barré syndrome, an immune-mediated neurological condition capable of producing severe weakness and reduced reflexes.

She received a five-day course of intravenous immunoglobulin, with partial improvement. However, subsequent laboratory results introduced another possibility. Blood testing revealed positive Borrelia IgM antibodies, and a second lumbar puncture identified Borrelia IgM antibodies in the cerebrospinal fluid, confirmed by immunoblot testing. The repeat cerebrospinal fluid examination also showed an elevated mononuclear white blood cell count.

Further questioning established that the patient lived in a rural area of England where tick exposure was plausible. She did not recall a tick bite and had not noticed the characteristic skin rash associated with Lyme disease. The absence of those features did not exclude the possibility of infection.

Clinicians subsequently administered intravenous ceftriaxone for 14 days. Her motor function improved significantly, and she regained the ability to walk with bilateral support. She was discharged with recommendations for continued physiotherapy and rehabilitation.

The authors considered atypical Lyme neuroborreliosis a possible explanation for her presentation. They also acknowledged that positive Borrelia antibodies alone were insufficient to establish the diagnosis, and that the neurological presentation was unusual. The improvement following antibiotics supported their interpretation but did not independently establish the precise cause of every neurological finding.


What About the Positive Hoover's Sign?

This is arguably the most interesting aspect of the case. Hoover's sign is commonly described as a positive clinical sign supporting functional limb weakness. It assesses changes in involuntary hip extension during contralateral hip flexion, with certain patterns interpreted as evidence of inconsistency between voluntary and automatic movement.

In this patient's case, an early examination reportedly identified a positive Hoover's sign. The clinicians also documented fluctuating weakness, emotional distress and a history of recent stress. Nevertheless, further investigation revealed electrophysiological abnormalities, cerebrospinal fluid changes and evidence supporting an infectious neurological process.

The paper does not provide enough information to independently evaluate how Hoover's sign was performed or whether the initial interpretation was correct. It therefore cannot establish that a properly demonstrated positive Hoover's sign was caused by neuroborreliosis. What it does demonstrate is that the reported sign did not settle the diagnostic question, and that the patient's neurological illness required continued investigation.

There is an important distinction between identifying an inconsistency during examination and establishing what caused it. A clinical sign may contribute to diagnostic reasoning, but it cannot automatically invalidate other abnormalities or justify disregarding subsequent evidence. In this case, the neurological findings evolved, and the diagnostic interpretation evolved with them.

Interestingly, the authors themselves acknowledged that conversion disorder remains a problematic diagnosis, particularly where symptoms are unusual and the distinction between functional and neurological disease is uncertain. Their discussion also references an earlier published case of Guillain-Barré syndrome being misdiagnosed as conversion disorder.


The Lesson From This Case

This report does not establish that the patient received a definitive FND diagnosis that was subsequently overturned. Conversion disorder was seriously considered during the initial assessment, while Guillain-Barré syndrome and later possible neuroborreliosis emerged through continued investigation. The final interpretation remained cautious, with the authors proposing an unusual presentation of neuroborreliosis rather than claiming absolute diagnostic certainty.

That distinction does not diminish the significance of the case. A patient presented with severe neurological impairment, objective abnormalities and clinical features interpreted as potentially functional. Had the investigation stopped at the reported inconsistencies, anxiety and Hoover's sign, the subsequent electrophysiological and infectious findings might never have been identified.

For anyone concerned about diagnostic overshadowing, the practical issue is straightforward: an apparent functional sign is not a substitute for explaining the full clinical presentation. Reduced reflexes, an extensor plantar response, progressive weakness and abnormal neurological investigations cannot simply be brushed aside because other findings appear inconsistent.

The case also raises a broader question relevant to the Common Phenotypes Hypothesis: whether some clinical patterns classified as functional may occur across different underlying neurological conditions. This individual report cannot establish that hypothesis, but it illustrates why the relationship between observable symptoms, examination signs and underlying disease mechanisms deserves careful scrutiny.

The authors ultimately demonstrated something more useful than diagnostic certainty at the first consultation: the importance of revisiting an initial interpretation when new evidence emerges. In a patient whose condition was worsening, continued investigation made the difference between an unresolved suspicion of functional symptoms and the identification of a potentially treatable neurological illness.


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