Objective: This is the first reported case of PERM made in a patient with profound mental retardation and we highlight the unusual features of his clinical course that lead to this rare diagnosis.

Background: PERM is a rare syndrome in which there is a varying combination of rigidity, stimulus-sensitive spasm, myoclonus, hyperekplexia and autonomic disturbances. PERM has significant clinical overlap with NMS.

Methods: Case report.

Results: A 32 year old male with profound mental retardation lately required psychiatric care due to worsening behavior and developed new neck movements. He had brief exposure to risperidone and chlorpromazine. He had a temperature of 39.4 degrees, heart rate of 107, marked neck and limb rigidity. He would turn his head from side to side, and had brief myoclonic movements in which he would extend his neck and posture his limbs. Creatine Kinase (CK) was elevated at 4779. MRI brain imaging and CSF studies were normal. A presumptive diagnosis of NMS was made and lorazepam started. Oddly, CK peaked at 17847 two weeks later. Rigidity worsened a month later. Fever, tachycardia and blood pressure variability persisted. 3 months later, he developed refractory status epilepticus. Anti-glycine antibodies was tested which was strongly positive in keeping with a diagnosis of PERM. The patient was treated with IV immunoglobulins. 2 weeks later, the autonomic instability had resolved completely. Post discharge, he has returned to premorbid status with no further neck turning.

Conclusions: The diagnosis of PERM is particularly challenging: MRI brain and CSF studies are frequently normal. Our patient would have fulfilled the diagnosis of NMS. However there were atypical features in his clinical course. Our patient developed new head-turning movements which was likely a behavioral response to the severe neck rigidity. Furthermore, myoclonus and refractory status epilepticus were present.The time course and severity of his condition was unusual: there was only brief exposure to low dose antipsychotics, however CK continued to peak a month later and degree of rigidity severe. Our case highlights the need for a high index of suspicion for PERM when the clinical picture of NMS is atypical, particularly in intellectually impaired patients where the significance of new behavioral changes is difficult to appreciate.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/progressive-encephalomyelitis-with-rigidity-and-myoclonus-perm-in-an-intellectually-disabled-patient-initially-misdiagnosed-as-neuroleptic-malignant-syndrome-nms/