Lambert-Eaton syndrome in neoplastic disease

This code represents Lambert-Eaton Myasthenic Syndrome (LEMS) that occurs as a paraneoplastic syndrome, meaning it is caused by an underlying malignancy. LEMS is an autoimmune disorder affecting the neuromuscular junction, leading to muscle weakness, particularly in the proximal limbs, and autonomic dysfunction. The body's immune system mistakenly attacks voltage-gated calcium channels on nerve endings, impairing acetylcholine release.

Use this code when documentation clearly links LEMS to a co-occurring neoplastic disease, such as small cell lung carcinoma, lymphoma, or other cancers. This diagnosis requires physician documentation explicitly stating the paraneoplastic nature of the LEMS. The underlying malignancy should also be coded.

• Always code the underlying neoplasm first, followed by this code, to accurately reflect the etiology.
• Do not use this code if the LEMS is idiopathic or not associated with a malignancy; refer to the Excludes1 note for appropriate non-neoplastic LEMS codes.
• Ensure the medical record explicitly states the connection between the LEMS and the neoplastic disease; simply having both conditions present is not sufficient without physician documentation of the paraneoplastic link.