Assuming a definitive autoimmune encephalitis-associated with anti-IgLON5 antibodies, we applied high-dose steroids monthly (1g methylprednisolone i.v. for five consecutive days) and his memory complaints, ataxia of extremities and peripheral neuropathy as well as sleeping dysfunction decreased.<h4>Conclusions</h4>Our findings broaden IgLON5 disease's clinical spectrum to include predominant and discrete figural memory impairment together with sleeping dysfunction at disease onset. The gene discussed is IGLON5; the disease is cerebellar ataxia.