Objective: To describe a case of anti-glutamic acid decarboxylase antibody (GAD-Abs)-associated cerebellar ataxia (CA), which presented with gradual dysautonomia and parkinsonism fulfilling criteria for MSA, representing a diagnostic challenge.

Background: After stiff person syndrome (SPS), CA is the second most frequent disorder associated with GAD-Abs. ¹ High levels of GAD-abs have been reported in patients with several syndromes, including SPS, epilepsy and limbic encephalitis, but there are few reports of parkinsonism and autonomic failure associated with GAD-Abs. The reason why some patients develop one neurological syndrome versus another is unclear. ²

Methods: We report a case of a 66-year-old male with a history of imbalance, motor incoordination and sexual dysfunction during six months. Later, the patient also developed dysarthria, dysphagia and urinary incontinency. He was admitted to our hospital with a global cerebellar and dysautonomic syndrome. During evaluation, autoimmune laboratory tests showed remarkably increased serum GAD-abs levels (3090, normal value:25). Electroneuromyography demonstrated dysautonomia in limbs, without stiff limb. Other laboratory tests, cerebral MRI, CSF and paraneoplastic investigation showed no abnormality.

Results: Initially, the prominent dysautonomia and cerebellar ataxia supported the diagnosis of MSA. The serum high levels of GAD-Abs, however, raised the suspicion of an inflammatory etiology. The patient first received corticosteroids with a poor response. Regardless of this fact, he proceeded four sessions of plasmapheresis and showed severe improvement of cerebellar symptoms and functionality.

Conclusions: This case illustrates an atypical presentation of a CA with dysautonomia associated with GAD-Abs mimicking MSA, revealing the importance of a thorough evaluation for late onset CA and suggesting that dysautomia could be a manifestation associated with GAD-Abs. The case also highlights the challenge of immunotherapy, despite the various types that have been used in patients with GAD Abs-CA, most patients remain with significant disability.

1. Saiz A et al. Spectrum of neurological syndromes associated with glutamic acid decarboxylase antibodies: diagnostic clues for this association. Brain. 2008;131(10):2553-2563. 2. Arino H et al. Cerebellar Ataxia and Glutamic Acid Decarboxylase Antibodies: Immunologic Profile and Long-term Effect of Immunotherapy. Jama Neurology. 2014; 71(8):1009-1016.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/anti-gad-antibody-cerebellar-ataxia-mimicking-multiple-system-atrophy/