A 62-year-old man presents to the clinic with progressive muscle weakness over the past few months. He describes an altered gait and difficulty rising from a seated position. He reports that his weakness improves with activity and is worse in the morning. He denies having rashes, fevers, or any double vision or drooping of the eyelids. His past medical history includes small cell lung cancer, hypertension, and chronic obstructive pulmonary disease (COPD). He is currently taking lisinopril, tiotropium, and albuterol. He has a 40-pack-year smoking history and drinks alcohol occasionally. His vital signs are within normal limits. Neurological examination reveals proximal muscle weakness in the legs that improves with repetitive stimulation. The rest of the physical examination is unremarkable.
C) Lambert-Eaton syndrome
Lambert-Eaton syndrome is associated with small cell carcinoma of the lung and results in a myasthenia gravis-like disease that spares the ocular muscles. It is a disorder of reduced acetylcholine release from the presynaptic nerve terminals. In Lambert-Eaton syndrome, the muscles actually become stronger with repetitive stimulation, which is the opposite of what is seen in myasthenia gravis. This patient's history of small cell lung carcinoma, the described symptoms of muscle weakness that improves with activity, and the examination findings of proximal muscle weakness that improves with repetitive stimulation strongly suggest Lambert-Eaton syndrome.
Answer choice A: Amyotrophic lateral sclerosis (ALS), is incorrect. ALS typically presents with both upper and lower motor neuron signs, such as muscle weakness, atrophy, fasciculations, and hyperreflexia but does not show improvement with repetitive muscle use.
Answer choice B: Guillain-Barré syndrome, is incorrect. Guillain-Barré syndrome typically presents with ascending muscle weakness and areflexia, but it does not improve with repetitive muscle use.
Answer choice D: Myasthenia gravis, is incorrect. Myasthenia gravis typically presents with muscle weakness that worsens with activity and often involves the ocular muscles, which is the opposite of what is seen in Lambert-Eaton syndrome.
Answer choice E: Polymyositis, is incorrect. Polymyositis presents with symmetric proximal muscle weakness and elevated muscle enzymes but does not improve with repetitive muscle use.
Key Learning Point
Lambert-Eaton syndrome is associated with small cell carcinoma of the lung and results in a myasthenia gravis-like disease that spares the ocular muscles. In Lambert-Eaton syndrome, the muscles actually become stronger with repetitive stimulation, which is the opposite of what is seen in myasthenia gravis.
