Facial pruritus and stiffness as the initial manifestations of glycine receptor antibody-positive progressive encephalomyelitis with rigidity and myoclonus: a case report and literature review

Progressive encephalomyelitis with rigidity and myoclonus (PERM) is a rare and severe phenotype within stiff-person spectrum disorders (SPSD), frequently associated with glycine receptor antibodies (GlyR-Ab). Because typical rigidity and stimulus-sensitive spasms may be absent at disease onset, early diagnosis can be challenging. We report a 52-year-old man who presented with facial pruritus, facial stiffness, limited tongue protrusion, dysphagia, and left lower-limb pain. Early manifestations included diplopia, restricted extraocular movements, dysarthria, restricted mouth opening, involuntary jaw closure resembling trismus, and involuntary tongue biting. Nonspecific oropharyngeal and maxillofacial abnormalities on imaging initially raised concern for infectious multiple cranial neuropathy, tetanus, or orofacial infection; however, antimicrobial therapy and symptomatic treatment with diazepam and pregabalin produced no sustained improvement. The subsequent emergence of neck, truncal, and lower-limb stiffness, gait impairment, perioral hypersensitivity, and stimulus-induced facial muscle contractions prompted reconsideration of SPSD. Needle electromyography (EMG) demonstrated continuous synchronous motor unit activity in agonist and antagonist muscles at rest. Serum antibody testing was positive for glycine receptor 1 immunoglobulin G (GlyR1-IgG), with a reported semiquantitative value of 1:100, whereas serum glutamic acid decarboxylase 65 (GAD65) antibody was negative, supporting the diagnosis of GlyR-Ab-positive PERM. The patient showed marked initial improvement following combined immunotherapy and symptomatic treatment. During regular follow-up, the patient’s symptoms progressively improved. At the latest follow-up, diplopia, facial sensory abnormalities, restricted mouth opening, and limb rigidity had resolved. Repeat serum testing at a different laboratory showed persistent GlyR1-IgG positivity, with a reported endpoint titer of 1:100; the two numerical results were not directly comparable because different titration protocols were used. The patient was advised to continue oral mycophenolate mofetil 500 mg twice daily as maintenance therapy. This case illustrates the diagnostic challenges of GlyR-Ab-positive PERM when facial pruritus and cranial-bulbar symptoms precede generalized stiffness. Recognition of evolving stimulus-induced muscle contractions, together with characteristic EMG findings and antibody testing, can help distinguish this presentation from infectious cranial neuropathy, tetanus, and local orofacial disease.