This is a case of suspected toxic (narcotic) leukoencephalopathy. 

The patient had a prolonged ICU and rehab admission with a subsequent acquired brain injury. 

A potential differential for the etiology underlying the leukoencephalopathy evident on MRI is a post-hypoxic encephalopathy. There is considerable overlap in the spectrum of the imaging appearance of the two entities. One of the hallmarks of delayed hypoxic encephalopathy is the clinical biphasic pattern of deterioration, which usually has an initial improvement and then neurological decline. 

In this case, the patient suffered a neurological insult fairly immediately and had a fluctuating GCS of 3-7 for several days in the ICU, with a spastic quadriparesis, and had only mildly improved with extensive rehab (i.e. there was no real recovery period as in the classic pattern for delayed hypoxic encephalopathy). While it remains relatively difficult to separate whether this case was secondary to the toxic stimulus or a related hypoxic event, the patient was thought to most likely have a toxic leukoencephalopathy.