Introduction

Foix–Chavany–Marie syndrome (FCMS) is a rare neurological disorder characterised by loss of voluntary control of the facial, lingual, pharyngeal and masticatory musculature despite preservation of involuntary and emotional movements, reflecting the phenomenon of automatic-voluntary dissociation. Although classically attributed to bilateral opercular lesions, alternative neuroanatomical mechanisms remain poorly recognised. We present an uncommon dual-lesion mechanism producing FCMS through disruption of bilateral corticobulbar pathways.

Case presentation

A 61-year-old man presented with abrupt onset anarthria and severe dysphagia while maintaining intact language comprehension, limb motor function, spontaneous smiling and yawning. Neurological examination demonstrated complete paralysis of voluntary orofacial movements with preserved emotional and reflexive facial activity, a hallmark of automatic-voluntary dissociation. Magnetic resonance imaging identified an acute left corona radiata infarction together with previously asymptomatic right frontal opercular polymicrogyria. Extensive laboratory investigations excluded inflammatory, infectious, neuromuscular and metabolic causes. Integration of the characteristic clinical phenotype with neuroimaging established the diagnosis of FCMS resulting from a functional bilateral corticobulbar disconnection rather than classical bilateral opercular infarction. Recognition of this rare mechanism was pivotal in distinguishing the syndrome from important clinical mimics including pseudobulbar palsy, myasthenia gravis, Guillain–Barré syndrome, brainstem stroke and catatonia, thereby avoiding unnecessary investigations and inappropriate therapeutic interventions.

Conclusion

This case broadens the recognised clinico-radiological spectrum of FCMS by demonstrating that an acute unilateral subcortical infarction may unmask a clinically silent contralateral congenital cortical malformation, producing a functional bilateral opercular syndrome. The report highlights the diagnostic value of meticulous neurological examination combined with targeted neuroimaging in identifying uncommon corticobulbar disconnection syndromes. Increased recognition of dual-lesion mechanisms may facilitate earlier diagnosis, prevent misdiagnosis, optimise acute stroke management, and expedite multidisciplinary rehabilitation in patients presenting with acute orofacial paralysis.

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