Background: Opsoclonus-myoclonus-ataxia syndrome (OMAS) is characterised by the acute or subacute development of chaotic eye movements and diffuse myoclonus. On some occasions it is associated with ataxia and encephalopathy. In adults there are multiple causations and a possible paraneoplastic origin must always be taken into account.

Methods: We report two cases of OMAS of a paraneoplastic origin with a post mortem study. In the first case, the syndrome was associated to a small-cell carcinoma in the lungs, and in the second patient it was associated to a digestive lymphoma. Neuroimaging studies did not reveal any kind of alterations in either of the two cases. In our cases, none of the antibodies that are relatively frequently associated to this syndrome were found. In both of them, an immunomodulator treatment regimen was established; only the patient with the lymphoma showed an initial improvement with antineoplastic therapy. In the pathological study, alterations were observed in the brain stem, and in the second patient alterations were also found in the cerebellum.

Conclusions: This is a rare condition that obliges the specialist to think in order to reach a correct diagnosis, and to search for the primary tumour and establish early treatment in order to bring about an improvement and even the remission of the neurological signs and symptoms. The pathological findings are not pathognomonic, but they are typical of this syndrome.