American Board of Psychiatry and Neurology (ABPN) Practice Exam 2026 - Free ABPN Practice Questions and Study Guide

The condition characterized by progressive muscle weakness in the context of lung cancer, along with improved strength with minimal exercise, is Lambert-Eaton myasthenic syndrome (LEMS). This syndrome is a neuromuscular junction disease where antibodies attack the voltage-gated calcium channels on presynaptic nerve terminals, leading to a reduced release of acetylcholine at the neuromuscular junction.

In patients with lung cancer, particularly small cell lung cancer, there is often a paraneoplastic association with LEMS. This reflects an autoimmune response triggered by the malignancy, where the body's immune system mistakenly targets the nerves that communicate with muscles. A significant feature of Lambert-Eaton is that muscle strength tends to improve with repetitive use, which is in contrast to myasthenia gravis, where strength diminishes with sustained activity.

This improvement after exercise is due to increased calcium influx causing greater neurotransmitter release when muscles are repeatedly stimulated. As such, individuals diagnosed with LEMS often experience a unique pattern of muscular symptoms that align with the described details, especially in the context of an underlying malignancy.