704 - Targeting Refractory Dystonic Anarthria with Trihexyphenidyl in a Pediatric Case of GAD65-Positive Stiff Person Syndrome

Thursday, February 19, 2026

5:00 PM - 6:30 PM AST

Presenting Author(s)

KP

Kelly Pellegrino, MD

Resident Physician
MedStar Georgetown National Rehabilitation Hospital
Washington, District of Columbia, United States

Co-Author(s)

AB

Anisa Noiwong Benbourenane, BS

Medical Student
George Washington University School of Medicine and Health Sciences
Washington, District of Columbia, United States
JB

John Michael Bravo, DO

Resident Physician
National Capital Consortium
Derwood, Maryland, United States

Corresponding Author(s)

MF

Melissa Fleming, MD

Attending Physician
Children's National Hospital
Washington, District of Columbia, United States
JB

Justin Burton, MD

Division Chief of Physical Medicine & Rehabilitation
Children's National Hospital
Washington, District of Columbia, United States

Submitter(s)

KP

Kelly Pellegrino, MD

MedStar Georgetown National Rehabilitation Hospital
Washington, District of Columbia, United States

Case Diagnosis: Stiff Person Syndrome

Case Description: A 12-year-old male with ADHD presented with subacute motor speech deficit, dysphagia, and progressive dystonia. Physical exam was notable for RUE dystonia and oromandibular and laryngeal dystonia with preserved comprehension resulting in anarthria. Initial treatment for presumed autoimmune encephalitis with corticosteroids, IVIG, and PLEX led to improvement in RUE dystonia but not oromotor dystonia. Workup revealed normal brain MRI, intermittent diffuse slowing on cEEG, negative Wilson’s disease workup, and positive GAD65 antibody (1:140; 553 nmol/L), suggesting pediatric Stiff Person Syndrome (SPS). Baclofen was started for dystonia. He required brief intubation for aspiration, during which baclofen was transitioned to IV diazepam. After extubation, trihexyphenidyl (Artane) was initiated for persistent dystonia. He progressed from anarthria to functional dysarthria and demonstrated improved RUE dystonia and active finger flexion. He was subsequently admitted to inpatient rehabilitation.

Discussions: SPS is a rare immune-mediated disorder characterized by rigidity and spasms of axial and proximal limb muscles. Estimated prevalence is 1-2 cases per million and it most commonly affects adult females; only ~5% of cases occur in children. SPS is associated with anti-GAD antibodies, which impairs GABA production. Subsequent impaired inhibition results in neuronal hyperexcitability that manifests as rigidity and spasms. Standard treatment includes GABA-enhancing agents (baclofen, benzodiazepines, gabapentin, vigabatrin) and immunomodulatory therapies (IVIG, rituximab). In this case, severe oromotor dystonia caused profound anarthria. Trihexyphenidyl, a centrally acting anticholinergic and first-line agent for pediatric dystonia, was added as an adjunct for refractory symptoms. The combination of these treatments resulted in significant functional improvement, particularly with phonation and hand function.

Conclusions: Early recognition of pediatric SPS is critical to prevent irreversible disability. Management with a combination of treatments is common for severe symptoms. While standard medications are typically chosen for their GABAergic mechanisms, trihexyphenidyl may be beneficial for management of dystonia.