Coexistence of Lambert-Eaton myasthenic syndrome and subacute cerebellar degeneration: differential effects of treatment.

A 61-year-old woman presented with two paraneoplastic neurologic disorders--Lambert-Eaton myasthenic syndrome (LEMS) and subacute cerebellar degeneration (SCD)--that antedated the diagnosis of small-cell carcinoma of the lung by 15 months. Plasmapheresis initiated before the identification of the tumor had a beneficial effect on LEMS but did not affect the SCD. Chemotherapy administered for treatment of the primary tumor was also associated with improvement of LEMS but, like plasmapheresis, had no effect on SCD. While the pathogenesis of both LEMS and SCD is thought to be mediated predominantly by humoral immune factors, a differential therapeutic response indicates that mechanisms of tissue damage or susceptibility to tissue injury, or both, differ in these two disorders.