Eaton Lambert Syndrome (ELS) is a rare disorder that affects the nerve impulses that control muscle movements. It is also known as Lambert-Eaton myasthenic syndrome, myasthenic syndrome of Lambert-Eaton, and Lambert's syndrome. These synonyms are used interchangeably to refer to the same condition that results in muscle weakness, fatigue, and difficulty in movement. ELS often occurs in people with autoimmune diseases or cancers. It is treated through medication and other therapies that focus on improving muscle strength and function. Though ELS is a complex condition, familiarizing oneself with its synonyms can enhance communication with medical professionals and others who have the condition.