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To the Editor Fernández-Espejo and colleagues1 describe a patient with retained covert awareness who had a sharp reduction of behavioral command following.
With use of neuroimaging techniques that do not rely on the patient’s ability to produce an external response, the authors1 were able to demonstrate a dissociation between preserved voluntary motor imagery and absent skeletal muscle movements. Fiber tractography then showed selective structural damage to the white matter fibers connecting the thalamus and M1 bilaterally. The conclusion was that altered motor thalamocortical circuits were the cause of absent external responsiveness in this covertly aware patient. However, absent behavioral motor responses could have been caused by concurrent peripheral nervous system and muscle pathology. Critical illness polyneuropathy (CIP) and critical illness myopathy (CIM) are major causes of paralysis in critically ill patients,2 including patients with neurologic issues.3 In a recent series, CIP was described in 16 of 22 vegetative or minimally conscious patients (73%).4
Latronico N. Peripheral Causes of Cognitive Motor Dissociation in Patients With Vegetative or Minimally Conscious State. JAMA Neurol. 2016;73(5):608. doi:10.1001/jamaneurol.2016.0140