Objective: To report a case of steroid-responsive hyperreflexia myoclonus syndrome.

Background: Progressive encephalomyelitis with rigidity and myoclonus (PERM) is a variant of stiff-person syndrome (SPS) characterized by brainstem dysfunction, hyperekplexia, dysautonomia, rigidity and myoclonus, and typically associated with glycine receptor α1 subunits (GlyR) antibodies (abs). In SPS including PERM several abs have been identified but not in all cases, in such antibody-negative cases the diagnosis is challenging.

Method: We report a case of GAD-negative steroid-responsive PERM-mimicking syndrome, in which neuronal surface (NS) abs were examined in serum/CSF with 1) tissue immunohistochemistry (IHC), 2) cell-based assay (CBA), and 3) live neurons.

Results: A 56-year-old man with a 4-year history of progressive walking difficulty presented to our hospital. On neurologic examination, cognitive function was intact, but he had facial hyperhidrosis, tongue tremulous movements, hyperreflexia, exaggerated patellar clonus, upgoing toes signs, spasticity in his legs, and hypokinetic/bradykinetic gait. Myoclonic jerks or 7-Hz clonic oscillations of quadriceps lasting two seconds were provoked by leg movements or a single tap on the patellar tendon with a hammer (confirmed on video/surface EMG). No hyperekplexia or stiffness was found. Laboratory test results were normal, including GAD abs, thyroid function, CSF analysis, and brain/spinal MRIs. Electrophysiological examinations including needle EMG did not reveal findings of peripheral nerve hyperexcitability or persistent motor unit activity, but showed hyperexcitability of the alpha motoneurons. Based on these findings, the patient was treated with intravenous methylprednisolone (IVMP), resulting in immediate and dramatic resolution of symptoms; he became able to run. However, eight days after IVMP, he relapsed again. He was treated with IVMP followed by oral prednisolone, resulting in resolution of symptoms. Antibody test results came back negative for all previously known NS antigens including GABAaR and GlyR. No immunoreactivity was seen on either tissue IHC or live neurons.

Conclusion: Based on the clinical features, this autoantibody-negative but steroid-responsive hyperreflexia myoclonus syndrome may be of immune-mediated origin, and could be a novel syndrome.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/autoantibody-negative-but-probable-autoimmune-hyperreflexia-myoclonus-syndrome-a-case-report/