A previously healthy 2 years and 1 month-old girl presented with 6 months of insidious decrease in social reciprocity (decreased eye contact, decreased interest in playing with toys and family), mild decrease in dexterity, and decreased overall physical activity.  This was followed by 2 months of accelerated progression characterized by:  loss of all speech (from speaking 3-4 word sentences), loss of all acquired purposeful hand skills with stereotyped hand wringing, loss of ambulation preceded by a period of repeated falls, irritability and irregular sleep patterns, loss of social reciprocity aside from preferential responsiveness to her mother, and generalized tonic seizures.  Brain MRI was normal.  She was diagnosed with Rett Syndrome based on the revised clinical diagnostic criteria (2010).  At 4 month follow-up, she had spontaneously regained ambulation (with persistent moderate ataxia), was able to feed herself, and had improving social communication.  MECP2 analysis was normal.  Further evaluation including CSF analysis revealed anti-NMDAR antibodies in the absence of pleocytosis or other immunological markers.  Treatment with high dose IV steroids and IVIg led to accelerated improvement.