Clinical outcome in adult onset idiopathic or paraneoplastic opsoclonus-myoclonus

We analysed a series of 24 adult patients with idiopathic (10 cases) and paraneoplastic (14 cases) opsoclonus–myoclonus syndrome (OMS) to ascertain possible differences in clinical course and response to immunotherapies between both groups. Associated tumours were small-cell lung cancer (SCLC) (nine patients), non-SCLC (one patient), breast carcinoma (two patients), gastric adenocarcinoma (one patient) and kidney carcinoma (one patient). Patients with paraneoplastic OMS were older [median age: 66 years versus 40 years (P = 0.006) of those with idiopathic OMS] and had a higher frequency of encephalopathy (64% versus 10%; P = 0.02). Serum from 10/10 idiopathic and 12/14 paraneoplastic OMS patients showed no specific immunoreactivity on rat or human brainstem or cerebellum, lacked specific antineuronal antibodies (Hu, Yo, Ri, Tr, glutamic acid decarboxylase, amphiphysin or CV2) and did not contain antibodies to voltage-gated calcium channels. The two paraneoplastic exceptions were a patient with SCLC, whose serum contained both anti-Hu and anti-amphiphysin antibodies and a patient with breast cancer who had serum anti-Ri antibodies. The clinical course of idiopathic OMS was monophasic except in two elderly women who had relapses of the opsoclonus and mild residual ataxia. Most idiopathic OMS patients made a good recovery, but residual gait ataxia tended to persist in older patients. Immunotherapy (mainly intravenous immunoglobulins or corticosteroids) seemed to accelerate recovery. Paraneoplastic OMS had a more severe clinical course, despite treatment with intravenous immunoglobulins or costicosteroids, and was the cause of death in five patients whose tumours were not treated. By contrast the eight patients whose tumours were treated showed a complete or partial neurological recovery. We conclude that idiopathic OMS occurs in younger patients, the clinical evolution is more benign and the effect of immunotherapy appears more effective than in paraneoplastic OMS. In patients aged 50 years and older with OMS who develop encephalopathy, early diagnosis and treatment of a probable underlying tumour, usually SCLC, is indicated to increase the chances of neurological recovery. At present, there are no immunological markers to identify the adult patients with paraneoplastic OMS.