Cerebellar ataxia and stiff person-syndrome are the main neurological syndromes associated with antibodies to glutamic acid decarboxylase (GAD).
A 59-year-old patient, with history of polymyalgia rheumatica and active smoking, was admitted for subacute cerebellar ataxia and memory dysfunction explained by limbic encephalitis on brain MRI. He also presented with orthostatic hypotension and erectile dysfunction revealing autonomic dysfunction. CSF was inflammatory and antibodies to GAD were positive. Onconeuronal antibodies including GABA(B) receptor antibodies were negative. Patient's condition quickly improved after intravenous immunoglobulins. A few months later, a small cell lung carcinoma was diagnosed and precociously treated.
This case report underlines the importance of appropriate studies to confirm a primitive neoplasia, when confronted with limbic encephalitis and cerebellar ataxia, even if anti-GAD antibodies rarely define paraneoplastic syndromes.