A dual manifestation of GAD-antibody spectrum disorder: a case of progressive encephalomyelitis with rigidity, myoclonus and autoimmune epilepsy with mesial temporal sclerosis

Progressive encephalomyelitis with rigidity and myoclonus (PERM) is a rare neurological disorder within the spectrum of stiff-person syndrome (SPS) and epilepsy, and is part of the group of GAD (glutamic acid decarboxylase) antibody-associated disorders. PERM diagnosis is often challenging due to its heterogeneous presentation, and treatment remains difficult, as clear therapeutic guidelines for this condition have yet to be established. To the best of our knowledge, no prior reports have documented the simultaneous occurrence of PERM and anti-GAD–positive autoimmune epilepsy associated with mesial temporal sclerosis (MTS), thus highlighting a previously unrecognised phenotype within the GAD-spectrum disorders. We present the case of a 32-year-old male with a progressive neurological syndrome characterised by lower limb rigidity, gait disturbance, painful spasms, and hyperekplexia. Over five years, he developed epileptic seizures, stimulus-induced myoclonus, and neuropsychiatric symptoms (emotional lability, depressive affect, anxiety). High titers of anti-GAD antibodies in serum, along with EMG findings, supported the diagnosis of PERM. Brain MRI revealed right MTS. Symptomatic treatment with GABAergic agents led to significant clinical improvement; immunotherapy was considered but not initially required due to the positive response. This case represents, to the best of our knowledge, the first reported instance of PERM coexisting with anti-GAD–positive autoimmune epilepsy and MTS, underscoring the clinical relevance of recognizing overlapping GAD-spectrum phenotypes to guide timely diagnosis and individualized management.