57.: Anti-glutamic acid decarboxylase antibody associated cerebellar ataxia and breast carcinoma

Abstract

This study aims to highlight the importance of screening for rare causes of acquired ataxia, and present a patient with paraneoplastic anti-Gad antibody cerebellar ataxia. A 79-year-old lady with a past history of Hashimoto’s thyroiditis, spinal ependymoma and noninsulin-dependent diabetes mellitus presented with a 1 month history of gait ataxia. There had been 5 kg unintentional weight loss over several months. Examination revealed gait ataxia without appendicular ataxia, dysarthria, or saccadic eye movement abnormalities. Gaze-evoked nystagmus was intermittently observed. Antineuronal antibodies, tumour markers, vasculitis/antiphospholipid antibody screens, coeliac serology, B12, folate, venereal disease research laboratory, and vitamin E tests were normal or negative. Thyroid-stimulating hormone was mildly elevated with normal T3 and T4 levels. Serum anti-GAD antibody levels were strikingly elevated (>2000 international units/ml). Cerebrospinal fluid (CSF) revealed 4 mononuclear cells. CSF oligoclonal bands were present. Nerve conduction studies did not reveal electrophysiological evidence of peripheral neuropathy. MRI/MR angiography of the brain revealed moderately severe microvascular ischaemic gliosis. MRI of the spine was unremarkable. CT scan of the chest, abdomen and pelvis did not reveal evidence of malignancy. Positron emission tomography scan revealed irregular fluorodeoxyglucose uptake in the thyroid gland and tissues of the right breast. Mammogram revealed three suspicious lesions in the right breast. Biopsy followed by wide local excision revealed invasive tubular carcinoma and low grade ductal carcinoma in situ. Intravenous immunoglobulin G was commenced 4 weeks prior to starting chemotherapy with letrozole. There was a significant improvement in gait ataxia 2 weeks after the second course of Intravenous immunoglobulin G. Anti-GAD antibody associated ataxia is well described, and cases usually respond to immunotherapy. An association with breast cancer has rarely been reported. This case suggests the importance of screening for an underlying malignancy in patients with anti-GAD antibody associated cerebellar ataxia.