La myasthénie est fréquemment associée à des maladies auto-immunes, mais rarement à d’autres affections neurologiques. Nous rapportons le cas d’un homme de 74 ans, hypertendu, hospitalisé pour apparition brutale d’un ptosis gauche et de troubles de la mastication. Il fut conclu à l’association d’une myasthénie et d’une polyradiculonévrite. Un traitement anticholinestérasique fut partiellement efficace. Les troubles persistant après un mois, une corticothérapie fut instaurée avec succès, permettant une résolution complète de la symptomatologie. L’hypothèse physiopathologique proposée est celle d’une origine auto-immune commune prenant des formes d’expression clinique différentes. La corticothérapie semble être la plus efficace devant ces formes particulières.

Although myasthenia gravis (MG) has frequently been associated with other autoimmune disorders, it has only rarely been reported in conjunction with diseases of the nervous system. A 74-year-old patient with hypertension suddenly presented left unilateral ptosis and mastication disorders. Clinical examination showed a concomitant loss of strength distally and reduced deep tendon reflex. Electrophysiologic data indicated a diagnosis of MG and chronic inflammatory demyelinating polyneuropathy ; acetylcholine receptor antibody was elevated at 4.1nmol/L (normal < 2nmol/L). Improvement was rapid after initiation of pyridostigmine in association with corticosteroid (1mg/kg/day). One month later, the cranial nerve deficit disappeared and strength was normal. It is likely that a basic abnormality of immune regulation was responsible for the emergence of diseases with different clinical presentations, but similar immunopathogenesis. Corticosteroid seemed to be the most effective treatment.