Progressive Encephalomyelitis with Rigidity and Myoclonus Treated with Rituximab: Case Report and Review of the Literature.

A woman in her 50s presented with hyper-religiosity, auditory hallucinations, episodes of staring associated with unresponsiveness and stiffening of her entire body. A broad workup excluded autoimmune encephalitis, sarcoidosis, and prion disease. She was diagnosed with PERM (progressive encephalomyelitis with rigidity and myoclonus) syndrome which was supported by elevated cerebrospinal fluid (CSF) autoantibodies against glutamic acid decarboxylase (GAD) glutamic acid decarboxylase. She responded to treatment with corticosteroids and weekly rituximab therapy over four weeks. PERM is an autoimmune condition which is a rare variant of stiff person syndrome involving rigidity, dysautonomia and encephalopathy. PERM requires the clinician to have a high index of clinical suspicion to recognize and treat.