We present an anti-glutamic acid decarboxylase (GAD) positive patient who developed stiff person syndrome five years after hospitalization for limbic encephalitis.

Syndromes linked to GAD antibodies include epilepsy, limbic encephalitis, stiff person syndrome, and cerebellar ataxia. Some anti-GAD positive patients display more than one syndrome. Literature review shows a wide variation in the timing of disease presentation in patients with overlapping disorders. There are very few reported instances of overlapping limbic encephalitis and stiff person syndrome.

A 28 year old female with a history of epilepsy was admitted for breakthrough seizures and altered mentation. She was alert only to self and displayed short term memory loss and repetitive speech. CSF showed normal cell count and protein, without any evidence of malignancy or infection. MRI revealed T2 enhancement in the medial left temporal lobe. Bilateral frontotemporal epileptiform discharges were seen on EEG. She developed psychosis and was treated with antipsychotics and antiepileptics. Upon discharge she was oriented x3 but still had amnesia. Her CSF autoimmune antibody panel returned with elevated GAD antibodies at 217 nmol/L (<0.02 nmol/L). A diagnosis of limbic encephalitis was made. Five years later, she presented with gait difficulty, back stiffness, hyperlordosis, and difficulty bending forward. CSF was notable for oligoclonal bands and anti-GAD level of 166 nmol/L. She was diagnosed with stiff person syndrome. Plasmapheresis resulted in moderate symptom improvement. She is now on a tapering dose of intravenous immunoglobulin. Her cognitive status remains poor, with a recent mental status exam score of 9/30.

Further study into the natural history and long-term outcomes of patients with GAD antibodies would be beneficial, but research remains challenging due to disease rarity. Clinicians managing patients with GAD antibodies should retain suspicion for the development of further anti-GAD diseases even years after the initial presentation.