Educational Disclaimer: This case study is for educational and informational purposes only. It does not constitute medical advice, clinical guidance, or a substitute for professional psychiatric evaluation. All diagnostic criteria referenced are from the DSM-5-TR (APA, 2022). Clinicians should rely on their professional training, direct patient assessment, and current evidence-based guidelines when making diagnostic and treatment decisions.

Clinical Vignette

Patient: "Mr. J," 38-year-old delivery driver, presenting with sudden onset left leg weakness 2 days ago that has left him unable to walk or work.

Chief Concern: "My left leg just stopped working 2 days ago. I woke up and it was like it wasn't there. I can't walk. I'm dragging it. I need to work — I'll lose my job."

History of Present Illness: Mr. J woke up 2 days ago with complete inability to use his left leg. He describes the onset as sudden (overnight). Before the onset, he had received notice that his brother had been sentenced to prison, which he describes as 'devastating.' He denies any fall, trauma, injury, numbness, or tingling. The leg feels 'dead' to him. He has been using a borrowed wheelchair. He denies any prior neurological symptoms. He has no headaches, visual changes, speech difficulties, or upper extremity weakness. He denies substance use. Physical examination reveals: (1) Hoover sign POSITIVE (involuntary hip extension of the 'weak' leg is present when he flexes the contralateral leg against resistance, but voluntary hip extension is 'impossible'). (2) Give-way weakness (the leg collapses suddenly during resistance testing rather than showing gradual failure). (3) Left leg strength is 0/5 on voluntary testing but 4/5 on involuntary testing (Hoover). (4) Reflexes are normal and symmetric bilaterally. (5) Sensory examination normal. (6) MRI brain and spine: normal.

Medical History: No neurological conditions. MRI brain and spine: normal.

Mental Status Exam: Anxious but cooperative. Appears genuinely distressed about the weakness. Speech normal. Mood 'scared.' Affect congruent. No psychotic symptoms. No la belle indifference (he is NOT indifferent; he is distressed). Insight minimal about psychological mechanism.

Step 1: FND (Conversion Disorder) DSM-5-TR Criteria — Motor Weakness

Criterion A: One or more symptoms of altered voluntary motor function.

Left leg weakness preventing ambulation. This is a motor symptom. MET.

Criterion B: Clinical findings provide evidence of incompatibility.

Hoover sign POSITIVE: involuntary hip extension at 4/5 strength proves that the motor pathway is intact. Give-way weakness (sudden collapse rather than gradual failure) is inconsistent with upper or lower motor neuron lesion. Normal reflexes bilaterally. Normal MRI brain and spine. MET — MULTIPLE POSITIVE SIGNS.

Criterion C: Not better explained by another disorder.

MS excluded (normal MRI). Stroke excluded (normal MRI, age, no vascular risk). GBS excluded (normal reflexes). Structural lesion excluded. MET.

Criterion D: Significant distress or impairment.

Unable to walk. Unable to work. Risk of job loss. MET.

Step 2: Positive Clinical Signs of Functional Weakness

Clinical Sign What It Tests Finding Interpretation
Hoover sign Involuntary contralateral hip extension during ipsilateral flexion against resistance POSITIVE: left leg extends involuntarily at 4/5 when right leg is flexed Motor pathway intact: weakness is functional
Give-way weakness Pattern of resistance during strength testing Sudden collapse rather than gradual failure Inconsistent with UMN/LMN pattern
Drift without pronation Pattern of limb drift when eyes closed Left arm shows no drift (control); left leg: functional pattern of weakness Dissociation between voluntary and involuntary function
Reflexes Lower motor neuron integrity Normal and symmetric Rules out LMN lesion
MRI brain/spine Structural lesion Normal Rules out MS, stroke, structural lesion

Positive Diagnosis

The Hoover sign is the gold standard positive clinical sign for functional limb weakness. It demonstrates that the motor neural pathway is anatomically intact (the leg CAN extend involuntarily) while the voluntary movement is impaired. This dissociation between voluntary and involuntary function is pathognomonic for functional neurological disorder.

Diagnostic Formulation

Diagnostic Conclusion

Conversion Disorder (FND), with Weakness (F44.4): All 4 DSM-5-TR criteria met. Positive Hoover sign confirms functional etiology. Normal MRI excludes structural lesion. Psychological precipitant identified (brother's imprisonment). Treatment: (1) Communicate diagnosis positively ('your brain's software has a problem, not the hardware — your motor pathways are intact'). (2) Physical rehabilitation (neurology-led physiotherapy tailored for FND). (3) CBT to address psychological factors. (4) Avoid unnecessary immobilization (wheelchair should be discontinued; weight-bearing encouraged).

Teaching Points

  • The Hoover sign is the most reliable positive clinical sign for functional leg weakness. It exploits the involuntary synkinetic pattern: when one hip flexes against resistance, the contralateral hip involuntarily extends. If a patient cannot voluntarily extend the 'weak' hip but demonstrates involuntary extension during contralateral flexion, the motor pathway is intact.
  • La belle indifference (apparent lack of concern about symptoms) was historically considered pathognomonic for conversion disorder but is NOT a reliable diagnostic sign. Research shows it occurs in neurological disease as well. Mr. J does NOT display la belle indifference — he is distressed. DSM-5-TR does not require it.
  • FND motor weakness requires positive clinical signs (Hoover, give-way weakness, drift without pronation), not merely absence of neurological findings. The diagnosis is made BY the positive signs, not by exclusion of all other possibilities.
  • Neurological physiotherapy for FND motor weakness uses specific techniques: distraction-based movement (performing the 'impossible' movement while attention is directed elsewhere), retraining automatic movements, and progressive weight-bearing. Standard rehabilitation protocols are less effective because they focus on the voluntary movements that are impaired.
  • DSM-5-TR explicitly removed the requirement for a psychological precipitant (previously required in DSM-IV). The diagnosis is made on the clinical signs alone. However, when a precipitant is identified (as in Mr. J's case), it should be documented and addressed in treatment.