Objective: Stiff person syndrome and cerebellar ataxia are immunological neurological syndromes associated with the presence of glutamic acid decarboxylase (GAD) antibodies.

Background: Patients with GAD associated cerebellar ataxia present with a progressive subacute or chronic cerebellar syndrome, which may be combined with other manifestations such as stiffness, oculomotor dysfunction, epilepsy and cognitive dysfunction. Other autoimmune disorders can be observed in patients with GAD ataxia such as diabetes mellitus or thyroiditis, while an underlying neoplasia has been reported in about 12% of the patients.

Method: We present a case of a 42-year-old woman, who presented with gait difficulty of subacute onset, dysarthria, double vision and painful spasms of the lower extremities. Family history was negative for ataxia or other movement disorders. Neurological examination revealed horizontal nystagmus, dysarthria, ataxia of the left upper and lower extremity and leg stiffness.

Results: Brain magnetic resonance imaging (MRI) excluded a structural lesion and cerebrovascular fluid (CSF) analysis excluded an inflammatory cause for her symptoms. The patient had high serum and CSF GAD antibodies (serum >12.000 IU/ml, CSF >120 IU/ml). Amphiphysin antibodies were negative in the CSF and a paraneoplasmatic origin could be excluded through computer tomography of the thorax, abdomen, mammography and colonoscopy. The patient was treated with 1 gr methylprednisolone intravenous daily for 5 days followed by 60mg/day oral methylprednisolone. She also received gabapentin 900 mg/d. At 3-month-follow-up she had a moderate improvement of ataxia and nystagmus, while immunotherapy with mycophenolate mofetil was started at that point.

Conclusion: GAD ataxia and stiff leg syndrome are rare neurological disorders, with a few other cases with both conditions reported in the literature. They can be adequately managed using steroids, intravenous immunoglobulin or other second line treatment such as azathioprine, rituximab and mycophenolate mofetil. Therefore, clinicians and movement disorders specialists should include them in the differential diagnosis of ataxia, especially in cases with negative family history.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-case-of-gad-ataxia-and-stiff-leg-syndrome/