We report a case of paraneoplastic myasthenic syndrome with clinical features 
suggesting Lambert Eaton syndrome but without the electromyographic elements 
required for diagnosis. Anti-calcium channel antibodies were also lacking. The 
electromyogram evidenced a block and the Tensilon test was positive. The 
efficacy of anticholinesterases argued in favor of myasthenia but 
anti-acetylcholine receptor antibodies were negative. The block was more of a 
mixed nature, involving both presynaptic transmission as in Lambert Eaton 
syndrome and post-synaptic transmission as in paraneoplastic myasthenia. The 
primary tumor was identified as a small-cell neuroendocrine lung carcinoma on 
mediastinal biopsies obtained directly on CT-scan guided puncture of a 
mediastinal node. Thoracotomy was thus avoided. The Lambert Eaton syndrome is a 
paraneoplastic manifestation of small-cell lung cancer in 50% of the cases 
unlike generalized myasthenia which apparently is never associated with 
small-cell lung cancer. A mixed paraneoplastic neuro-muscle junction disorder 
with aspects of each can be exceptionally observed.