The anatomy of concealed awareness: lessons from partial locked-in syndrome

Partial locked-in syndrome (PLIS) is a rare stroke presentation in which preserved consciousness is masked by severe motor impairment, potentially leading to misinterpretation as encephalopathy. We report a patient in her early seventies with vascular risk factors and a prior pontine infarct who presented with acute quadriplegia and mutism. Initial clinical impressions raised concern for altered mental status. However, subsequent neurological examination demonstrated preserved awareness, with consistent eye tracking and command following through head movements. Examination showed bifacial and bulbar weakness, severe dysarthria, and minimal right arm movement. MRI demonstrated new infarcts in the left cerebral peduncle, posterior limb of the internal capsule, thalamus, and temporal lobe, superimposed on a prior pontine lesion. This distributed but strategically located pattern of injury affected bilateral corticospinal pathways and explained the profound motor impairment despite preserved consciousness. This case highlights how PLIS may mimic encephalopathy in the acute care setting and underscores the importance of structured bedside assessment for detecting preserved awareness in mute or immobile patients. Early recognition has implications for airway management, stroke evaluation, communication strategies, and prognostic counseling.