Abstract
Locked-in syndrome (LIS) is a state of quadriplegia and anarthria with preserved consciousness, which is generally triggered by a disruption of specific white matter fiber tracts, following a lesion in the ventral part of the pons. However, the impact of focal lesions on the whole brain white matter microstructure and structural connectivity pathways remains unknown. We used diffusion tensor magnetic resonance imaging (DT-MRI) and tract-based statistics to characterise the whole white matter tracts in seven consecutive LIS patients, with ventral pontine injuries but no significant supratentorial lesions detected with morphological MRI. The imaging was performed in the acute phase of the disease (26 ± 13 days after the accident). DT-MRI-derived metrics were used to quantitatively assess global white matter alterations. All diffusion coefficient Z-scores were decreased for almost all fiber tracts in all LIS patients, with diffuse white matter alterations in both infratentorial and supratentorial areas. A mixture model of two multidimensional Gaussian distributions was fitted to cluster the white matter fiber tracts studied in two groups: the least (group 1) and most injured white matter fiber tracts (group 2). The greatest injuries were revealed along pathways crossing the lesion responsible for the LIS: left and right medial lemniscus (98.4% and 97.9% probability of belonging to group 2, respectively), left and right superior cerebellar peduncles (69.3% and 45.7% probability) and left and right corticospinal tract (20.6% and 46.5% probability). This approach demonstrated globally compromised white matter tracts in the acute phase of LIS, potentially underlying cognitive deficits.
Highlights
Locked-in syndrome (LIS) was defined by Plum and Posner in 1966 as a condition in which selective supramotor de-efferentiation produces paralysis of all four limbs and the lower cranial nerves without interfering with consciousness [1]
LIS can be divided into three categories depending on the extent of motor impairment: classical LIS refers to Plum and Posner’s definition of patients with total immobility except for vertical eye movements and blinking; incomplete LIS refers to patients with preserved voluntary movements, other than vertical eye movements and blinking; total LIS refers to patients with total immobility including all eye movements [2]
We explored the potential of diffusion tensor magnetic resonance imaging (DT-MRI) and a subsequent tract-based statistics approach applied to DT-MRI-derived metrics
Summary
Locked-in syndrome (LIS) was defined by Plum and Posner in 1966 as a condition in which selective supramotor de-efferentiation produces paralysis of all four limbs and the lower cranial nerves without interfering with consciousness [1]. Lateral eye movements are generally impossible due to damage to either the lateral gaze centre (adjacent to the nucleus of the abducens nerve) or its connexions with the cortex. Vertical eye movements are spared because the vertical gaze centre is located in or just above the superior colliculi. LIS patients usually have partially preserved cutaneous sensation. The medial lemniscus located on the dorsal side of the pyramidal tracts is usually disrupted, but the more laterally located spinothalamic tract is generally spared
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